This patch-set deals with an interesting yet stupid problem: kernel code
that does not get inlined despite its simplicity. There are several
causes for this behavior: "cold" attribute on __init, different function
optimization levels; conditional constant computations based on
__builtin_constant_p(); and finally large inline assembly blocks.
This patch-set deals with the inline assembly problem. I separated these
patches from the others (that were sent in the RFC) for easier
inclusion. I also separated the removal of unnecessary new-lines which
would be sent separately.
The problem with inline assembly is that inline assembly is often used
by the kernel for things that are other than code - for example,
assembly directives and data. GCC however is oblivious to the content of
the blocks and assumes their cost in space and time is proportional to
the number of the perceived assembly "instruction", according to the
number of newlines and semicolons. Alternatives, paravirt and other
mechanisms are affected, causing code not to be inlined, and degrading
compilation quality in general.
The solution that this patch-set carries for this problem is to create
an assembly macro, and then call it from the inline assembly block. As
a result, the compiler sees a single "instruction" and assigns the more
appropriate cost to the code.
To avoid uglification of the code, as many noted, the macros are first
precompiled into an assembly file, which is later assembled together
with the C files. This also enables to avoid duplicate implementation
that was set before for the asm and C code. This can be seen in the
exception table changes.
Overall this patch-set slightly increases the kernel size (my build was
done using my Ubuntu 18.04 config + localyesconfig for the record):
text data bss dec hex filename
18140829 10224724 2957312 31322865 1ddf2f1 ./vmlinux before
18163608 10227348 2957312 31348268 1de562c ./vmlinux after (+0.1%)
The number of static functions in the image is reduced by 379, but
actually inlining is even better, which does not always shows in these
numbers: a function may be inlined causing the calling function not to
be inlined.
I ran some limited number of benchmarks, and in general the performance
impact is not very notable. You can still see >10 cycles shaved off some
syscalls that manipulate page-tables (e.g., mprotect()), in which
paravirt caused many functions not to be inlined. In addition this
patch-set can prevent issues such as [1], and improves code readability
and maintainability.
[1] https://patchwork.kernel.org/patch/10450037/
v6->v7: * Fix context switch tracking (Ingo)
* Fix xtensa build error (Ingo)
* Rebase on 4.18-rc8
v5->v6: * Removing more code from jump-labels (PeterZ)
* Fix build issue on i386 (0-day, PeterZ)
v4->v5: * Makefile fixes (Masahiro, Sam)
v3->v4: * Changed naming of macros in 2 patches (PeterZ)
* Minor cleanup of the paravirt patch
v2->v3: * Several build issues resolved (0-day)
* Wrong comments fix (Josh)
* Change asm vs C order in refcount (Kees)
v1->v2: * Compiling the macros into a separate .s file, improving
readability (Linus)
* Improving assembly formatting, applying most of the comments
according to my judgment (Jan)
* Adding exception-table, cpufeature and jump-labels
* Removing new-line cleanup; to be submitted separately
Cc: Masahiro Yamada <[email protected]>
Cc: Sam Ravnborg <[email protected]>
Cc: Alok Kataria <[email protected]>
Cc: Christopher Li <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jan Beulich <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Kate Stewart <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: [email protected]
Cc: Peter Zijlstra <[email protected]>
Cc: Philippe Ombredanne <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: Linus Torvalds <[email protected]>
Cc: [email protected]
Cc: Chris Zankel <[email protected]>
Cc: Max Filippov <[email protected]>
Cc: [email protected]
Nadav Amit (10):
xtensa: defining LINKER_SCRIPT for the linker script
Makefile: Prepare for using macros for inline asm
x86: objtool: use asm macro for better compiler decisions
x86: refcount: prevent gcc distortions
x86: alternatives: macrofy locks for better inlining
x86: bug: prevent gcc distortions
x86: prevent inline distortion by paravirt ops
x86: extable: use macros instead of inline assembly
x86: cpufeature: use macros instead of inline assembly
x86: jump-labels: use macros instead of inline assembly
Makefile | 9 ++-
arch/x86/Makefile | 11 ++-
arch/x86/entry/calling.h | 2 +-
arch/x86/include/asm/alternative-asm.h | 20 ++++--
arch/x86/include/asm/alternative.h | 11 +--
arch/x86/include/asm/asm.h | 61 +++++++---------
arch/x86/include/asm/bug.h | 98 +++++++++++++++-----------
arch/x86/include/asm/cpufeature.h | 82 ++++++++++++---------
arch/x86/include/asm/jump_label.h | 77 ++++++++------------
arch/x86/include/asm/paravirt_types.h | 56 +++++++--------
arch/x86/include/asm/refcount.h | 74 +++++++++++--------
arch/x86/kernel/macros.S | 16 +++++
arch/xtensa/kernel/Makefile | 4 +-
include/asm-generic/bug.h | 8 +--
include/linux/compiler.h | 56 +++++++++++----
scripts/Kbuild.include | 4 +-
scripts/mod/Makefile | 2 +
17 files changed, 333 insertions(+), 258 deletions(-)
create mode 100644 arch/x86/kernel/macros.S
--
2.17.1
Use assembly macros for static_cpu_has() and call them from inline
assembly. This not only makes the code more readable, but also improves
compilation decision, specifically inline decisions which GCC base on
the number of new lines in inline assembly.
The patch slightly increases the kernel size:
text data bss dec hex filename
18162879 10226256 2957312 31346447 1de4f0f ./vmlinux before
18163528 10226300 2957312 31347140 1de51c4 ./vmlinux after (+693)
And enables the inlining of function such as free_ldt_pgtables().
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
arch/x86/include/asm/cpufeature.h | 82 ++++++++++++++++++-------------
arch/x86/kernel/macros.S | 1 +
2 files changed, 48 insertions(+), 35 deletions(-)
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index aced6c9290d6..7d442722ef24 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -2,10 +2,10 @@
#ifndef _ASM_X86_CPUFEATURE_H
#define _ASM_X86_CPUFEATURE_H
-#include <asm/processor.h>
-
-#if defined(__KERNEL__) && !defined(__ASSEMBLY__)
+#ifdef __KERNEL__
+#ifndef __ASSEMBLY__
+#include <asm/processor.h>
#include <asm/asm.h>
#include <linux/bitops.h>
@@ -161,37 +161,10 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
*/
static __always_inline __pure bool _static_cpu_has(u16 bit)
{
- asm_volatile_goto("1: jmp 6f\n"
- "2:\n"
- ".skip -(((5f-4f) - (2b-1b)) > 0) * "
- "((5f-4f) - (2b-1b)),0x90\n"
- "3:\n"
- ".section .altinstructions,\"a\"\n"
- " .long 1b - .\n" /* src offset */
- " .long 4f - .\n" /* repl offset */
- " .word %P[always]\n" /* always replace */
- " .byte 3b - 1b\n" /* src len */
- " .byte 5f - 4f\n" /* repl len */
- " .byte 3b - 2b\n" /* pad len */
- ".previous\n"
- ".section .altinstr_replacement,\"ax\"\n"
- "4: jmp %l[t_no]\n"
- "5:\n"
- ".previous\n"
- ".section .altinstructions,\"a\"\n"
- " .long 1b - .\n" /* src offset */
- " .long 0\n" /* no replacement */
- " .word %P[feature]\n" /* feature bit */
- " .byte 3b - 1b\n" /* src len */
- " .byte 0\n" /* repl len */
- " .byte 0\n" /* pad len */
- ".previous\n"
- ".section .altinstr_aux,\"ax\"\n"
- "6:\n"
- " testb %[bitnum],%[cap_byte]\n"
- " jnz %l[t_yes]\n"
- " jmp %l[t_no]\n"
- ".previous\n"
+ asm_volatile_goto("STATIC_CPU_HAS bitnum=%[bitnum] "
+ "cap_byte=\"%[cap_byte]\" "
+ "feature=%P[feature] t_yes=%l[t_yes] "
+ "t_no=%l[t_no] always=%P[always]"
: : [feature] "i" (bit),
[always] "i" (X86_FEATURE_ALWAYS),
[bitnum] "i" (1 << (bit & 7)),
@@ -226,5 +199,44 @@ static __always_inline __pure bool _static_cpu_has(u16 bit)
#define CPU_FEATURE_TYPEVAL boot_cpu_data.x86_vendor, boot_cpu_data.x86, \
boot_cpu_data.x86_model
-#endif /* defined(__KERNEL__) && !defined(__ASSEMBLY__) */
+#else /* __ASSEMBLY__ */
+
+.macro STATIC_CPU_HAS bitnum:req cap_byte:req feature:req t_yes:req t_no:req always:req
+1:
+ jmp 6f
+2:
+ .skip -(((5f-4f) - (2b-1b)) > 0) * ((5f-4f) - (2b-1b)),0x90
+3:
+ .section .altinstructions,"a"
+ .long 1b - . /* src offset */
+ .long 4f - . /* repl offset */
+ .word \always /* always replace */
+ .byte 3b - 1b /* src len */
+ .byte 5f - 4f /* repl len */
+ .byte 3b - 2b /* pad len */
+ .previous
+ .section .altinstr_replacement,"ax"
+4:
+ jmp \t_no
+5:
+ .previous
+ .section .altinstructions,"a"
+ .long 1b - . /* src offset */
+ .long 0 /* no replacement */
+ .word \feature /* feature bit */
+ .byte 3b - 1b /* src len */
+ .byte 0 /* repl len */
+ .byte 0 /* pad len */
+ .previous
+ .section .altinstr_aux,"ax"
+6:
+ testb \bitnum,\cap_byte
+ jnz \t_yes
+ jmp \t_no
+ .previous
+.endm
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __KERNEL__ */
#endif /* _ASM_X86_CPUFEATURE_H */
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
index 7baa40d5bf16..bf8b9c93e255 100644
--- a/arch/x86/kernel/macros.S
+++ b/arch/x86/kernel/macros.S
@@ -12,3 +12,4 @@
#include <asm/bug.h>
#include <asm/paravirt.h>
#include <asm/asm.h>
+#include <asm/cpufeature.h>
--
2.17.1
Use assembly macros for jump-labels and call them from inline assembly.
This not only makes the code more readable, but also improves
compilation decision, specifically inline decisions which GCC base on
the number of new lines in inline assembly.
As a result the code size is slightly increased.
text data bss dec hex filename
18163528 10226300 2957312 31347140 1de51c4 ./vmlinux before
18163608 10227348 2957312 31348268 1de562c ./vmlinux after (+1128)
And functions such as intel_pstate_adjust_policy_max(),
kvm_cpu_accept_dm_intr(), kvm_register_readl() are inlined.
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Kate Stewart <[email protected]>
Cc: Philippe Ombredanne <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
arch/x86/entry/calling.h | 2 +-
arch/x86/include/asm/jump_label.h | 77 +++++++++++--------------------
arch/x86/kernel/macros.S | 1 +
3 files changed, 30 insertions(+), 50 deletions(-)
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 352e70cd33e8..708b46a54578 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -338,7 +338,7 @@ For 32-bit we have the following conventions - kernel is built with
.macro CALL_enter_from_user_mode
#ifdef CONFIG_CONTEXT_TRACKING
#ifdef HAVE_JUMP_LABEL
- STATIC_JUMP_IF_FALSE .Lafter_call_\@, context_tracking_enabled, def=0
+ STATIC_BRANCH_JMP l_yes=.Lafter_call_\@, key=context_tracking_enabled, branch=1
#endif
call enter_from_user_mode
.Lafter_call_\@:
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index 8c0de4282659..4606a7101f97 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -2,19 +2,6 @@
#ifndef _ASM_X86_JUMP_LABEL_H
#define _ASM_X86_JUMP_LABEL_H
-#ifndef HAVE_JUMP_LABEL
-/*
- * For better or for worse, if jump labels (the gcc extension) are missing,
- * then the entire static branch patching infrastructure is compiled out.
- * If that happens, the code in here will malfunction. Raise a compiler
- * error instead.
- *
- * In theory, jump labels and the static branch patching infrastructure
- * could be decoupled to fix this.
- */
-#error asm/jump_label.h included on a non-jump-label kernel
-#endif
-
#define JUMP_LABEL_NOP_SIZE 5
#ifdef CONFIG_X86_64
@@ -28,18 +15,27 @@
#ifndef __ASSEMBLY__
+#ifndef HAVE_JUMP_LABEL
+/*
+ * For better or for worse, if jump labels (the gcc extension) are missing,
+ * then the entire static branch patching infrastructure is compiled out.
+ * If that happens, the code in here will malfunction. Raise a compiler
+ * error instead.
+ *
+ * In theory, jump labels and the static branch patching infrastructure
+ * could be decoupled to fix this.
+ */
+#error asm/jump_label.h included on a non-jump-label kernel
+#endif
+
#include <linux/stringify.h>
#include <linux/types.h>
static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
{
- asm_volatile_goto("1:"
- ".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
- ".pushsection __jump_table, \"aw\" \n\t"
- _ASM_ALIGN "\n\t"
- _ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"
- ".popsection \n\t"
- : : "i" (key), "i" (branch) : : l_yes);
+ asm_volatile_goto("STATIC_BRANCH_NOP l_yes=\"%l[l_yes]\" key=\"%c0\" "
+ "branch=\"%c1\""
+ : : "i" (key), "i" (branch) : : l_yes);
return false;
l_yes:
@@ -48,13 +44,8 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
{
- asm_volatile_goto("1:"
- ".byte 0xe9\n\t .long %l[l_yes] - 2f\n\t"
- "2:\n\t"
- ".pushsection __jump_table, \"aw\" \n\t"
- _ASM_ALIGN "\n\t"
- _ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"
- ".popsection \n\t"
+ asm_volatile_goto("STATIC_BRANCH_JMP l_yes=\"%l[l_yes]\" key=\"%c0\" "
+ "branch=\"%c1\""
: : "i" (key), "i" (branch) : : l_yes);
return false;
@@ -76,35 +67,23 @@ struct jump_entry {
#else /* __ASSEMBLY__ */
-.macro STATIC_JUMP_IF_TRUE target, key, def
-.Lstatic_jump_\@:
- .if \def
- /* Equivalent to "jmp.d32 \target" */
- .byte 0xe9
- .long \target - .Lstatic_jump_after_\@
-.Lstatic_jump_after_\@:
- .else
- .byte STATIC_KEY_INIT_NOP
- .endif
+.macro STATIC_BRANCH_NOP l_yes:req key:req branch:req
+1:
+ .byte STATIC_KEY_INIT_NOP
.pushsection __jump_table, "aw"
_ASM_ALIGN
- _ASM_PTR .Lstatic_jump_\@, \target, \key
+ _ASM_PTR 1b, \l_yes, \key + \branch
.popsection
.endm
-.macro STATIC_JUMP_IF_FALSE target, key, def
-.Lstatic_jump_\@:
- .if \def
- .byte STATIC_KEY_INIT_NOP
- .else
- /* Equivalent to "jmp.d32 \target" */
- .byte 0xe9
- .long \target - .Lstatic_jump_after_\@
-.Lstatic_jump_after_\@:
- .endif
+.macro STATIC_BRANCH_JMP l_yes:req key:req branch:req
+1:
+ .byte 0xe9
+ .long \l_yes - 2f
+2:
.pushsection __jump_table, "aw"
_ASM_ALIGN
- _ASM_PTR .Lstatic_jump_\@, \target, \key + 1
+ _ASM_PTR 1b, \l_yes, \key + \branch
.popsection
.endm
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
index bf8b9c93e255..161c95059044 100644
--- a/arch/x86/kernel/macros.S
+++ b/arch/x86/kernel/macros.S
@@ -13,3 +13,4 @@
#include <asm/paravirt.h>
#include <asm/asm.h>
#include <asm/cpufeature.h>
+#include <asm/jump_label.h>
--
2.17.1
GCC considers the number of statements in inlined assembly blocks,
according to new-lines and semicolons, as an indication to the cost of
the block in time and space. This data is distorted by the kernel code,
which puts information in alternative sections. As a result, the
compiler may perform incorrect inlining and branch optimizations.
The solution is to set an assembly macro and call it from the inlined
assembly block. As a result GCC considers the inline assembly block as
a single instruction.
The effect of the patch is a more aggressive inlining, which also
causes a size increase of kernel.
text data bss dec hex filename
18147336 10226688 2957312 31331336 1de1408 ./vmlinux before
18162555 10226288 2957312 31346155 1de4deb ./vmlinux after (+14819)
Static text symbols:
Before: 40053
After: 39942 (-111)
Cc: Alok Kataria <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: [email protected]
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
arch/x86/include/asm/paravirt_types.h | 56 +++++++++++++--------------
arch/x86/kernel/macros.S | 1 +
2 files changed, 28 insertions(+), 29 deletions(-)
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 180bc0bff0fb..dd55d3d1c32a 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -343,23 +343,11 @@ extern struct pv_lock_ops pv_lock_ops;
#define paravirt_clobber(clobber) \
[paravirt_clobber] "i" (clobber)
-/*
- * Generate some code, and mark it as patchable by the
- * apply_paravirt() alternate instruction patcher.
- */
-#define _paravirt_alt(insn_string, type, clobber) \
- "771:\n\t" insn_string "\n" "772:\n" \
- ".pushsection .parainstructions,\"a\"\n" \
- _ASM_ALIGN "\n" \
- _ASM_PTR " 771b\n" \
- " .byte " type "\n" \
- " .byte 772b-771b\n" \
- " .short " clobber "\n" \
- ".popsection\n"
-
/* Generate patchable code, with the default asm parameters. */
-#define paravirt_alt(insn_string) \
- _paravirt_alt(insn_string, "%c[paravirt_typenum]", "%c[paravirt_clobber]")
+#define paravirt_call \
+ "PARAVIRT_CALL type=\"%c[paravirt_typenum]\"" \
+ " clobber=\"%c[paravirt_clobber]\"" \
+ " pv_opptr=\"%c[paravirt_opptr]\";"
/* Simple instruction patching code. */
#define NATIVE_LABEL(a,x,b) "\n\t.globl " a #x "_" #b "\n" a #x "_" #b ":\n\t"
@@ -387,16 +375,6 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
int paravirt_disable_iospace(void);
-/*
- * This generates an indirect call based on the operation type number.
- * The type number, computed in PARAVIRT_PATCH, is derived from the
- * offset into the paravirt_patch_template structure, and can therefore be
- * freely converted back into a structure offset.
- */
-#define PARAVIRT_CALL \
- ANNOTATE_RETPOLINE_SAFE \
- "call *%c[paravirt_opptr];"
-
/*
* These macros are intended to wrap calls through one of the paravirt
* ops structs, so that they can be later identified and patched at
@@ -534,7 +512,7 @@ int paravirt_disable_iospace(void);
/* since this condition will never hold */ \
if (sizeof(rettype) > sizeof(unsigned long)) { \
asm volatile(pre \
- paravirt_alt(PARAVIRT_CALL) \
+ paravirt_call \
post \
: call_clbr, ASM_CALL_CONSTRAINT \
: paravirt_type(op), \
@@ -544,7 +522,7 @@ int paravirt_disable_iospace(void);
__ret = (rettype)((((u64)__edx) << 32) | __eax); \
} else { \
asm volatile(pre \
- paravirt_alt(PARAVIRT_CALL) \
+ paravirt_call \
post \
: call_clbr, ASM_CALL_CONSTRAINT \
: paravirt_type(op), \
@@ -571,7 +549,7 @@ int paravirt_disable_iospace(void);
PVOP_VCALL_ARGS; \
PVOP_TEST_NULL(op); \
asm volatile(pre \
- paravirt_alt(PARAVIRT_CALL) \
+ paravirt_call \
post \
: call_clbr, ASM_CALL_CONSTRAINT \
: paravirt_type(op), \
@@ -691,6 +669,26 @@ struct paravirt_patch_site {
extern struct paravirt_patch_site __parainstructions[],
__parainstructions_end[];
+#else /* __ASSEMBLY__ */
+
+/*
+ * This generates an indirect call based on the operation type number.
+ * The type number, computed in PARAVIRT_PATCH, is derived from the
+ * offset into the paravirt_patch_template structure, and can therefore be
+ * freely converted back into a structure offset.
+ */
+.macro PARAVIRT_CALL type:req clobber:req pv_opptr:req
+771: ANNOTATE_RETPOLINE_SAFE
+ call *\pv_opptr
+772: .pushsection .parainstructions,"a"
+ _ASM_ALIGN
+ _ASM_PTR 771b
+ .byte \type
+ .byte 772b-771b
+ .short \clobber
+ .popsection
+.endm
+
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_PARAVIRT_TYPES_H */
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
index 66ccb8e823b1..71d8b716b111 100644
--- a/arch/x86/kernel/macros.S
+++ b/arch/x86/kernel/macros.S
@@ -10,3 +10,4 @@
#include <asm/refcount.h>
#include <asm/alternative-asm.h>
#include <asm/bug.h>
+#include <asm/paravirt.h>
--
2.17.1
GCC considers the number of statements in inlined assembly blocks,
according to new-lines and semicolons, as an indication to the cost of
the block in time and space. This data is distorted by the kernel code,
which puts information in alternative sections. As a result, the
compiler may perform incorrect inlining and branch optimizations.
The solution is to set an assembly macro and call it from the inlinedv
assembly block. As a result GCC considers the inline assembly block as
a single instruction.
This patch increases the kernel size:
text data bss dec hex filename
18146889 10225380 2957312 31329581 1de0d2d ./vmlinux before
18147336 10226688 2957312 31331336 1de1408 ./vmlinux after (+1755)
But enables more aggressive inlining (and probably branch decisions).
The number of static text symbols in vmlinux is lower.
Static text symbols:
Before: 40218
After: 40053 (-165)
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: Josh Poimboeuf <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
arch/x86/include/asm/bug.h | 98 ++++++++++++++++++++++----------------
arch/x86/kernel/macros.S | 1 +
include/asm-generic/bug.h | 8 ++--
3 files changed, 61 insertions(+), 46 deletions(-)
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 6804d6642767..5090035e6d16 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -4,6 +4,8 @@
#include <linux/stringify.h>
+#ifndef __ASSEMBLY__
+
/*
* Despite that some emulators terminate on UD2, we use it for WARN().
*
@@ -20,53 +22,15 @@
#define LEN_UD2 2
-#ifdef CONFIG_GENERIC_BUG
-
-#ifdef CONFIG_X86_32
-# define __BUG_REL(val) ".long " __stringify(val)
-#else
-# define __BUG_REL(val) ".long " __stringify(val) " - 2b"
-#endif
-
-#ifdef CONFIG_DEBUG_BUGVERBOSE
-
-#define _BUG_FLAGS(ins, flags) \
-do { \
- asm volatile("1:\t" ins "\n" \
- ".pushsection __bug_table,\"aw\"\n" \
- "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
- "\t" __BUG_REL(%c0) "\t# bug_entry::file\n" \
- "\t.word %c1" "\t# bug_entry::line\n" \
- "\t.word %c2" "\t# bug_entry::flags\n" \
- "\t.org 2b+%c3\n" \
- ".popsection" \
- : : "i" (__FILE__), "i" (__LINE__), \
- "i" (flags), \
- "i" (sizeof(struct bug_entry))); \
-} while (0)
-
-#else /* !CONFIG_DEBUG_BUGVERBOSE */
-
#define _BUG_FLAGS(ins, flags) \
do { \
- asm volatile("1:\t" ins "\n" \
- ".pushsection __bug_table,\"aw\"\n" \
- "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
- "\t.word %c0" "\t# bug_entry::flags\n" \
- "\t.org 2b+%c1\n" \
- ".popsection" \
- : : "i" (flags), \
+ asm volatile("ASM_BUG ins=\"" ins "\" file=%c0 line=%c1 " \
+ "flags=%c2 size=%c3" \
+ : : "i" (__FILE__), "i" (__LINE__), \
+ "i" (flags), \
"i" (sizeof(struct bug_entry))); \
} while (0)
-#endif /* CONFIG_DEBUG_BUGVERBOSE */
-
-#else
-
-#define _BUG_FLAGS(ins, flags) asm volatile(ins)
-
-#endif /* CONFIG_GENERIC_BUG */
-
#define HAVE_ARCH_BUG
#define BUG() \
do { \
@@ -82,4 +46,54 @@ do { \
#include <asm-generic/bug.h>
+#else /* __ASSEMBLY__ */
+
+#ifdef CONFIG_GENERIC_BUG
+
+#ifdef CONFIG_X86_32
+.macro __BUG_REL val:req
+ .long \val
+.endm
+#else
+.macro __BUG_REL val:req
+ .long \val - 2b
+.endm
+#endif
+
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+
+.macro ASM_BUG ins:req file:req line:req flags:req size:req
+1: \ins
+ .pushsection __bug_table,"aw"
+2: __BUG_REL val=1b # bug_entry::bug_addr
+ __BUG_REL val=\file # bug_entry::file
+ .word \line # bug_entry::line
+ .word \flags # bug_entry::flags
+ .org 2b+\size
+ .popsection
+.endm
+
+#else /* !CONFIG_DEBUG_BUGVERBOSE */
+
+.macro ASM_BUG ins:req file:req line:req flags:req size:req
+1: \ins
+ .pushsection __bug_table,"aw"
+2: __BUG_REL val=1b # bug_entry::bug_addr
+ .word \flags # bug_entry::flags
+ .org 2b+\size
+ .popsection
+.endm
+
+#endif /* CONFIG_DEBUG_BUGVERBOSE */
+
+#else /* CONFIG_GENERIC_BUG */
+
+.macro ASM_BUG ins:req file:req line:req flags:req size:req
+ \ins
+.endm
+
+#endif /* CONFIG_GENERIC_BUG */
+
+#endif /* __ASSEMBLY__ */
+
#endif /* _ASM_X86_BUG_H */
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
index 852487a9fc56..66ccb8e823b1 100644
--- a/arch/x86/kernel/macros.S
+++ b/arch/x86/kernel/macros.S
@@ -9,3 +9,4 @@
#include <linux/compiler.h>
#include <asm/refcount.h>
#include <asm/alternative-asm.h>
+#include <asm/bug.h>
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index a7613e1b0c87..cf7f4ef4749e 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -17,10 +17,8 @@
#ifndef __ASSEMBLY__
#include <linux/kernel.h>
-#ifdef CONFIG_BUG
-
-#ifdef CONFIG_GENERIC_BUG
struct bug_entry {
+#ifdef CONFIG_GENERIC_BUG
#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
unsigned long bug_addr;
#else
@@ -35,8 +33,10 @@ struct bug_entry {
unsigned short line;
#endif
unsigned short flags;
-};
#endif /* CONFIG_GENERIC_BUG */
+};
+
+#ifdef CONFIG_BUG
/*
* Don't use BUG() or BUG_ON() unless there's really no way out; one
--
2.17.1
Use assembly macros for exception-tables and call them from inline
assembly. This not only makes the code more readable and allows to
avoid the duplicate implementation, but also improves compilation
decision, specifically inline decisions which GCC base on the number of
new lines in inline assembly.
text data bss dec hex filename
18162555 10226288 2957312 31346155 1de4deb ./vmlinux before
18162879 10226256 2957312 31346447 1de4f0f ./vmlinux after (+292)
This allows to inline functions such as nested_vmx_exit_reflected(),
set_segment_reg(), __copy_xstate_to_user().
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: Josh Poimboeuf <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
arch/x86/include/asm/asm.h | 61 +++++++++++++++++---------------------
arch/x86/kernel/macros.S | 1 +
2 files changed, 28 insertions(+), 34 deletions(-)
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 990770f9e76b..e47a2256c64e 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -117,28 +117,44 @@
# define CC_OUT(c) [_cc_ ## c] "=qm"
#endif
-/* Exception table entry */
#ifdef __ASSEMBLY__
# define _ASM_EXTABLE_HANDLE(from, to, handler) \
- .pushsection "__ex_table","a" ; \
- .balign 4 ; \
- .long (from) - . ; \
- .long (to) - . ; \
- .long (handler) - . ; \
- .popsection
+ ASM_EXTABLE_HANDLE from to handler
+
+#else /* __ASSEMBLY__ */
+
+# define _ASM_EXTABLE_HANDLE(from, to, handler) \
+ "ASM_EXTABLE_HANDLE from=" #from " to=" #to \
+ " handler=\"" #handler "\"\n\t"
+
+/* For C file, we already have NOKPROBE_SYMBOL macro */
+
+#endif /* __ASSEMBLY__ */
-# define _ASM_EXTABLE(from, to) \
+#define _ASM_EXTABLE(from, to) \
_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
-# define _ASM_EXTABLE_FAULT(from, to) \
+#define _ASM_EXTABLE_FAULT(from, to) \
_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
-# define _ASM_EXTABLE_EX(from, to) \
+#define _ASM_EXTABLE_EX(from, to) \
_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
-# define _ASM_EXTABLE_REFCOUNT(from, to) \
+#define _ASM_EXTABLE_REFCOUNT(from, to) \
_ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
+/* Exception table entry */
+#ifdef __ASSEMBLY__
+
+.macro ASM_EXTABLE_HANDLE from:req to:req handler:req
+ .pushsection "__ex_table","a"
+ .balign 4
+ .long (\from) - .
+ .long (\to) - .
+ .long (\handler) - .
+ .popsection
+.endm
+
# define _ASM_NOKPROBE(entry) \
.pushsection "_kprobe_blacklist","aw" ; \
_ASM_ALIGN ; \
@@ -169,29 +185,6 @@
_ASM_EXTABLE(101b,103b)
.endm
-#else
-# define _EXPAND_EXTABLE_HANDLE(x) #x
-# define _ASM_EXTABLE_HANDLE(from, to, handler) \
- " .pushsection \"__ex_table\",\"a\"\n" \
- " .balign 4\n" \
- " .long (" #from ") - .\n" \
- " .long (" #to ") - .\n" \
- " .long (" _EXPAND_EXTABLE_HANDLE(handler) ") - .\n" \
- " .popsection\n"
-
-# define _ASM_EXTABLE(from, to) \
- _ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
-
-# define _ASM_EXTABLE_FAULT(from, to) \
- _ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
-
-# define _ASM_EXTABLE_EX(from, to) \
- _ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
-
-# define _ASM_EXTABLE_REFCOUNT(from, to) \
- _ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
-
-/* For C file, we already have NOKPROBE_SYMBOL macro */
#endif
#ifndef __ASSEMBLY__
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
index 71d8b716b111..7baa40d5bf16 100644
--- a/arch/x86/kernel/macros.S
+++ b/arch/x86/kernel/macros.S
@@ -11,3 +11,4 @@
#include <asm/alternative-asm.h>
#include <asm/bug.h>
#include <asm/paravirt.h>
+#include <asm/asm.h>
--
2.17.1
GCC considers the number of statements in inlined assembly blocks,
according to new-lines and semicolons, as an indication to the cost of
the block in time and space. This data is distorted by the kernel code,
which puts information in alternative sections. As a result, the
compiler may perform incorrect inlining and branch optimizations.
In the case of objtool, this distortion is extreme, since anyhow the
annotations of objtool are discarded during linkage.
The solution is to set an assembly macro and call it from the inline
assembly block. As a result GCC considers the inline assembly block as
a single instruction.
This patch slightly increases the kernel size.
text data bss dec hex filename
18140829 10224724 2957312 31322865 1ddf2f1 ./vmlinux before
18140970 10225412 2957312 31323694 1ddf62e ./vmlinux after (+829)
Static text symbols:
Before: 40321
After: 40302 (-19)
Cc: Christopher Li <[email protected]>
Cc: [email protected]
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
arch/x86/kernel/macros.S | 2 ++
include/linux/compiler.h | 56 ++++++++++++++++++++++++++++++----------
2 files changed, 45 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
index cfc1c7d1a6eb..cee28c3246dc 100644
--- a/arch/x86/kernel/macros.S
+++ b/arch/x86/kernel/macros.S
@@ -5,3 +5,5 @@
* commonly used. The macros are precompiled into assmebly file which is later
* assembled together with each compiled file.
*/
+
+#include <linux/compiler.h>
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 42506e4d1f53..2688f0d826e9 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -99,22 +99,13 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
* unique, to convince GCC not to merge duplicate inline asm statements.
*/
#define annotate_reachable() ({ \
- asm volatile("%c0:\n\t" \
- ".pushsection .discard.reachable\n\t" \
- ".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__COUNTER__)); \
+ asm volatile("ANNOTATE_REACHABLE counter=%c0" \
+ : : "i" (__COUNTER__)); \
})
#define annotate_unreachable() ({ \
- asm volatile("%c0:\n\t" \
- ".pushsection .discard.unreachable\n\t" \
- ".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__COUNTER__)); \
+ asm volatile("ANNOTATE_UNREACHABLE counter=%c0" \
+ : : "i" (__COUNTER__)); \
})
-#define ASM_UNREACHABLE \
- "999:\n\t" \
- ".pushsection .discard.unreachable\n\t" \
- ".long 999b - .\n\t" \
- ".popsection\n\t"
#else
#define annotate_reachable()
#define annotate_unreachable()
@@ -280,6 +271,45 @@ unsigned long read_word_at_a_time(const void *addr)
#endif /* __KERNEL__ */
+#else /* __ASSEMBLY__ */
+
+#ifdef __KERNEL__
+#ifndef LINKER_SCRIPT
+
+#ifdef CONFIG_STACK_VALIDATION
+.macro ANNOTATE_UNREACHABLE counter:req
+\counter:
+ .pushsection .discard.unreachable
+ .long \counter\()b -.
+ .popsection
+.endm
+
+.macro ANNOTATE_REACHABLE counter:req
+\counter:
+ .pushsection .discard.reachable
+ .long \counter\()b -.
+ .popsection
+.endm
+
+.macro ASM_UNREACHABLE
+999:
+ .pushsection .discard.unreachable
+ .long 999b - .
+ .popsection
+.endm
+#else /* CONFIG_STACK_VALIDATION */
+.macro ANNOTATE_UNREACHABLE counter:req
+.endm
+
+.macro ANNOTATE_REACHABLE counter:req
+.endm
+
+.macro ASM_UNREACHABLE
+.endm
+#endif /* CONFIG_STACK_VALIDATION */
+
+#endif /* LINKER_SCRIPT */
+#endif /* __KERNEL__ */
#endif /* __ASSEMBLY__ */
#ifndef __optimize
--
2.17.1
Using macros for inline assembly improves both readability and
compilation decisions that are distorted by big assembly blocks that use
alternative sections. Compile macros.S and use it to assemble all C
files. Currently, only x86 will use it.
Cc: Sam Ravnborg <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Michal Marek <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: [email protected]
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
Makefile | 9 +++++++--
arch/x86/Makefile | 11 +++++++++--
arch/x86/kernel/macros.S | 7 +++++++
scripts/Kbuild.include | 4 +++-
scripts/mod/Makefile | 2 ++
5 files changed, 28 insertions(+), 5 deletions(-)
create mode 100644 arch/x86/kernel/macros.S
diff --git a/Makefile b/Makefile
index 7a3c4548162b..39d790e74e0d 100644
--- a/Makefile
+++ b/Makefile
@@ -1051,7 +1051,7 @@ scripts: scripts_basic include/config/auto.conf include/config/tristate.conf \
# version.h and scripts_basic is processed / created.
# Listed in dependency order
-PHONY += prepare archprepare prepare0 prepare1 prepare2 prepare3
+PHONY += prepare archprepare macroprepare prepare0 prepare1 prepare2 prepare3
# prepare3 is used to check if we are building in a separate output directory,
# and if so do:
@@ -1075,7 +1075,9 @@ prepare1: prepare2 $(version_h) $(autoksyms_h) include/generated/utsrelease.h \
include/config/auto.conf
$(cmd_crmodverdir)
-archprepare: archheaders archscripts prepare1 scripts_basic
+macroprepare: prepare1 archmacros
+
+archprepare: archheaders archscripts macroprepare scripts_basic
prepare0: archprepare gcc-plugins
$(Q)$(MAKE) $(build)=.
@@ -1143,6 +1145,9 @@ archheaders:
PHONY += archscripts
archscripts:
+PHONY += archmacros
+archmacros:
+
PHONY += __headers
__headers: $(version_h) scripts_basic uapi-asm-generic archheaders archscripts
$(Q)$(MAKE) $(build)=scripts build_unifdef
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index a08e82856563..a4b90ac1629b 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -235,8 +235,8 @@ ifdef CONFIG_X86_64
LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
endif
-# Speed up the build
-KBUILD_CFLAGS += -pipe
+# We cannot use -pipe flag since we give an additional .s file to the compiler
+#KBUILD_CFLAGS += -pipe
# Workaround for a gcc prelease that unfortunately was shipped in a suse release
KBUILD_CFLAGS += -Wno-sign-compare
#
@@ -258,6 +258,13 @@ archscripts: scripts_basic
archheaders:
$(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all
+archmacros:
+ $(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s
+
+ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s
+export ASM_MACRO_FLAGS
+KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)
+
###
# Kernel objects
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
new file mode 100644
index 000000000000..cfc1c7d1a6eb
--- /dev/null
+++ b/arch/x86/kernel/macros.S
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * This file includes headers whose assembly part includes macros which are
+ * commonly used. The macros are precompiled into assmebly file which is later
+ * assembled together with each compiled file.
+ */
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 86321f06461e..d7b7aadb6cd8 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -115,7 +115,9 @@ __cc-option = $(call try-run,\
# Do not attempt to build with gcc plugins during cc-option tests.
# (And this uses delayed resolution so the flags will be up to date.)
-CC_OPTION_CFLAGS = $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS))
+# In addition, do not include the asm macros which are built later.
+CC_OPTION_FILTERED = $(GCC_PLUGINS_CFLAGS) $(ASM_MACRO_FLAGS)
+CC_OPTION_CFLAGS = $(filter-out $(CC_OPTION_FILTERED),$(KBUILD_CFLAGS))
# cc-option
# Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)
diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
index 42c5d50f2bcc..a5b4af47987a 100644
--- a/scripts/mod/Makefile
+++ b/scripts/mod/Makefile
@@ -4,6 +4,8 @@ OBJECT_FILES_NON_STANDARD := y
hostprogs-y := modpost mk_elfconfig
always := $(hostprogs-y) empty.o
+CFLAGS_REMOVE_empty.o := $(ASM_MACRO_FLAGS)
+
modpost-objs := modpost.o file2alias.o sumversion.o
devicetable-offsets-file := devicetable-offsets.h
--
2.17.1
Defining the LINKER_SCRIPT when building the linker script as being done
in other architectures. This is required for the next Makefile changes
would otherwise break things.
Cc: Chris Zankel <[email protected]>
Cc: Max Filippov <[email protected]>
Cc: [email protected]
Signed-off-by: Nadav Amit <[email protected]>
---
arch/xtensa/kernel/Makefile | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/xtensa/kernel/Makefile b/arch/xtensa/kernel/Makefile
index 91907590d183..8dff506caf07 100644
--- a/arch/xtensa/kernel/Makefile
+++ b/arch/xtensa/kernel/Makefile
@@ -35,8 +35,8 @@ sed-y = -e ':a; s/\*(\([^)]*\)\.text\.unlikely/*(\1.literal.unlikely .{text}.unl
-e 's/\.{text}/.text/g'
quiet_cmd__cpp_lds_S = LDS $@
-cmd__cpp_lds_S = $(CPP) $(cpp_flags) -P -C -Uxtensa -D__ASSEMBLY__ $< \
- | sed $(sed-y) >$@
+cmd__cpp_lds_S = $(CPP) $(cpp_flags) -P -C -Uxtensa -D__ASSEMBLY__ \
+ -DLINKER_SCRIPT $< | sed $(sed-y) >$@
$(obj)/vmlinux.lds: $(src)/vmlinux.lds.S FORCE
$(call if_changed_dep,_cpp_lds_S)
--
2.17.1
On Thu, Aug 9, 2018 at 1:15 PM, Nadav Amit <[email protected]> wrote:
> Defining the LINKER_SCRIPT when building the linker script as being done
> in other architectures. This is required for the next Makefile changes
> would otherwise break things.
>
> Cc: Chris Zankel <[email protected]>
> Cc: Max Filippov <[email protected]>
> Cc: [email protected]
> Signed-off-by: Nadav Amit <[email protected]>
> ---
> arch/xtensa/kernel/Makefile | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
Acked-by: Max Filippov <[email protected]>
--
Thanks.
-- Max
GCC considers the number of statements in inlined assembly blocks,
according to new-lines and semicolons, as an indication to the cost of
the block in time and space. This data is distorted by the kernel code,
which puts information in alternative sections. As a result, the
compiler may perform incorrect inlining and branch optimizations.
The solution is to set an assembly macro and call it from the inlined
assembly block. As a result GCC considers the inline assembly block as
a single instruction.
This patch handles the LOCK prefix, allowing more aggresive inlining.
text data bss dec hex filename
18140140 10225284 2957312 31322736 1ddf270 ./vmlinux before
18146889 10225380 2957312 31329581 1de0d2d ./vmlinux after (+6845)
Static text symbols:
Before: 40286
After: 40218 (-68)
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: Josh Poimboeuf <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
arch/x86/include/asm/alternative-asm.h | 20 ++++++++++++++------
arch/x86/include/asm/alternative.h | 11 ++---------
arch/x86/kernel/macros.S | 1 +
3 files changed, 17 insertions(+), 15 deletions(-)
diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h
index 31b627b43a8e..8e4ea39e55d0 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -7,16 +7,24 @@
#include <asm/asm.h>
#ifdef CONFIG_SMP
- .macro LOCK_PREFIX
-672: lock
+.macro LOCK_PREFIX_HERE
.pushsection .smp_locks,"a"
.balign 4
- .long 672b - .
+ .long 671f - . # offset
.popsection
- .endm
+671:
+.endm
+
+.macro LOCK_PREFIX insn:vararg
+ LOCK_PREFIX_HERE
+ lock \insn
+.endm
#else
- .macro LOCK_PREFIX
- .endm
+.macro LOCK_PREFIX_HERE
+.endm
+
+.macro LOCK_PREFIX insn:vararg
+.endm
#endif
/*
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 4cd6a3b71824..d7faa16622d8 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -31,15 +31,8 @@
*/
#ifdef CONFIG_SMP
-#define LOCK_PREFIX_HERE \
- ".pushsection .smp_locks,\"a\"\n" \
- ".balign 4\n" \
- ".long 671f - .\n" /* offset */ \
- ".popsection\n" \
- "671:"
-
-#define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
-
+#define LOCK_PREFIX_HERE "LOCK_PREFIX_HERE\n\t"
+#define LOCK_PREFIX "LOCK_PREFIX "
#else /* ! CONFIG_SMP */
#define LOCK_PREFIX_HERE ""
#define LOCK_PREFIX ""
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
index f1fe1d570365..852487a9fc56 100644
--- a/arch/x86/kernel/macros.S
+++ b/arch/x86/kernel/macros.S
@@ -8,3 +8,4 @@
#include <linux/compiler.h>
#include <asm/refcount.h>
+#include <asm/alternative-asm.h>
--
2.17.1
GCC considers the number of statements in inlined assembly blocks,
according to new-lines and semicolons, as an indication to the cost of
the block in time and space. This data is distorted by the kernel code,
which puts information in alternative sections. As a result, the
compiler may perform incorrect inlining and branch optimizations.
The solution is to set an assembly macro and call it from the inlined
assembly block. As a result GCC considers the inline assembly block as
a single instruction.
This patch allows to inline functions such as __get_seccomp_filter().
Interestingly, this allows more aggressive inlining while reducing the
kernel size.
text data bss dec hex filename
18140970 10225412 2957312 31323694 1ddf62e ./vmlinux before
18140140 10225284 2957312 31322736 1ddf270 ./vmlinux after (-958)
Static text symbols:
Before: 40302
After: 40286 (-16)
Functions such as kref_get(), free_user(), fuse_file_get() now get
inlined.
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: Kees Cook <[email protected]>
Cc: Jan Beulich <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Nadav Amit <[email protected]>
---
arch/x86/include/asm/refcount.h | 74 ++++++++++++++++++++-------------
arch/x86/kernel/macros.S | 1 +
2 files changed, 46 insertions(+), 29 deletions(-)
diff --git a/arch/x86/include/asm/refcount.h b/arch/x86/include/asm/refcount.h
index 4cf11d88d3b3..6b2809a4d8e9 100644
--- a/arch/x86/include/asm/refcount.h
+++ b/arch/x86/include/asm/refcount.h
@@ -4,6 +4,41 @@
* x86-specific implementation of refcount_t. Based on PAX_REFCOUNT from
* PaX/grsecurity.
*/
+
+#ifdef __ASSEMBLY__
+
+#include <asm/asm.h>
+#include <asm/bug.h>
+
+.macro REFCOUNT_EXCEPTION counter:req
+ .pushsection .text..refcount
+111: lea \counter, %_ASM_CX
+112: ud2
+ ASM_UNREACHABLE
+ .popsection
+113: _ASM_EXTABLE_REFCOUNT(112b, 113b)
+.endm
+
+/* Trigger refcount exception if refcount result is negative. */
+.macro REFCOUNT_CHECK_LT_ZERO counter:req
+ js 111f
+ REFCOUNT_EXCEPTION counter="\counter"
+.endm
+
+/* Trigger refcount exception if refcount result is zero or negative. */
+.macro REFCOUNT_CHECK_LE_ZERO counter:req
+ jz 111f
+ REFCOUNT_CHECK_LT_ZERO counter="\counter"
+.endm
+
+/* Trigger refcount exception unconditionally. */
+.macro REFCOUNT_ERROR counter:req
+ jmp 111f
+ REFCOUNT_EXCEPTION counter="\counter"
+.endm
+
+#else /* __ASSEMBLY__ */
+
#include <linux/refcount.h>
/*
@@ -14,34 +49,11 @@
* central refcount exception. The fixup address for the exception points
* back to the regular execution flow in .text.
*/
-#define _REFCOUNT_EXCEPTION \
- ".pushsection .text..refcount\n" \
- "111:\tlea %[counter], %%" _ASM_CX "\n" \
- "112:\t" ASM_UD2 "\n" \
- ASM_UNREACHABLE \
- ".popsection\n" \
- "113:\n" \
- _ASM_EXTABLE_REFCOUNT(112b, 113b)
-
-/* Trigger refcount exception if refcount result is negative. */
-#define REFCOUNT_CHECK_LT_ZERO \
- "js 111f\n\t" \
- _REFCOUNT_EXCEPTION
-
-/* Trigger refcount exception if refcount result is zero or negative. */
-#define REFCOUNT_CHECK_LE_ZERO \
- "jz 111f\n\t" \
- REFCOUNT_CHECK_LT_ZERO
-
-/* Trigger refcount exception unconditionally. */
-#define REFCOUNT_ERROR \
- "jmp 111f\n\t" \
- _REFCOUNT_EXCEPTION
static __always_inline void refcount_add(unsigned int i, refcount_t *r)
{
asm volatile(LOCK_PREFIX "addl %1,%0\n\t"
- REFCOUNT_CHECK_LT_ZERO
+ "REFCOUNT_CHECK_LT_ZERO counter=\"%[counter]\""
: [counter] "+m" (r->refs.counter)
: "ir" (i)
: "cc", "cx");
@@ -50,7 +62,7 @@ static __always_inline void refcount_add(unsigned int i, refcount_t *r)
static __always_inline void refcount_inc(refcount_t *r)
{
asm volatile(LOCK_PREFIX "incl %0\n\t"
- REFCOUNT_CHECK_LT_ZERO
+ "REFCOUNT_CHECK_LT_ZERO counter=\"%[counter]\""
: [counter] "+m" (r->refs.counter)
: : "cc", "cx");
}
@@ -58,7 +70,7 @@ static __always_inline void refcount_inc(refcount_t *r)
static __always_inline void refcount_dec(refcount_t *r)
{
asm volatile(LOCK_PREFIX "decl %0\n\t"
- REFCOUNT_CHECK_LE_ZERO
+ "REFCOUNT_CHECK_LE_ZERO counter=\"%[counter]\""
: [counter] "+m" (r->refs.counter)
: : "cc", "cx");
}
@@ -66,13 +78,15 @@ static __always_inline void refcount_dec(refcount_t *r)
static __always_inline __must_check
bool refcount_sub_and_test(unsigned int i, refcount_t *r)
{
- GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl", REFCOUNT_CHECK_LT_ZERO,
+ GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl",
+ "REFCOUNT_CHECK_LT_ZERO counter=\"%0\"",
r->refs.counter, "er", i, "%0", e, "cx");
}
static __always_inline __must_check bool refcount_dec_and_test(refcount_t *r)
{
- GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl", REFCOUNT_CHECK_LT_ZERO,
+ GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl",
+ "REFCOUNT_CHECK_LT_ZERO counter=\"%0\"",
r->refs.counter, "%0", e, "cx");
}
@@ -90,7 +104,7 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)
/* Did we try to increment from/to an undesirable state? */
if (unlikely(c < 0 || c == INT_MAX || result < c)) {
- asm volatile(REFCOUNT_ERROR
+ asm volatile("REFCOUNT_ERROR counter=\"%[counter]\""
: : [counter] "m" (r->refs.counter)
: "cc", "cx");
break;
@@ -106,4 +120,6 @@ static __always_inline __must_check bool refcount_inc_not_zero(refcount_t *r)
return refcount_add_not_zero(1, r);
}
+#endif /* __ASSEMBLY__ */
+
#endif
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
index cee28c3246dc..f1fe1d570365 100644
--- a/arch/x86/kernel/macros.S
+++ b/arch/x86/kernel/macros.S
@@ -7,3 +7,4 @@
*/
#include <linux/compiler.h>
+#include <asm/refcount.h>
--
2.17.1
Hi Nadav,
2018-08-10 5:15 GMT+09:00 Nadav Amit <[email protected]>:
> Using macros for inline assembly improves both readability and
> compilation decisions that are distorted by big assembly blocks that use
> alternative sections. Compile macros.S and use it to assemble all C
> files. Currently, only x86 will use it.
>
> Cc: Sam Ravnborg <[email protected]>
> Cc: Masahiro Yamada <[email protected]>
I added this in the previous version.
Acked-by: Masahiro Yamada <[email protected]>
When you send a new version,
please make sure to add Acked-by/Reviewed-by reviewers have given.
Thanks.
> Cc: Michal Marek <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: "H. Peter Anvin" <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Acked-by: Peter Zijlstra (Intel) <[email protected]>
> Signed-off-by: Nadav Amit <[email protected]>
> ---
> Makefile | 9 +++++++--
> arch/x86/Makefile | 11 +++++++++--
> arch/x86/kernel/macros.S | 7 +++++++
> scripts/Kbuild.include | 4 +++-
> scripts/mod/Makefile | 2 ++
> 5 files changed, 28 insertions(+), 5 deletions(-)
> create mode 100644 arch/x86/kernel/macros.S
>
> diff --git a/Makefile b/Makefile
> index 7a3c4548162b..39d790e74e0d 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1051,7 +1051,7 @@ scripts: scripts_basic include/config/auto.conf include/config/tristate.conf \
> # version.h and scripts_basic is processed / created.
>
> # Listed in dependency order
> -PHONY += prepare archprepare prepare0 prepare1 prepare2 prepare3
> +PHONY += prepare archprepare macroprepare prepare0 prepare1 prepare2 prepare3
>
> # prepare3 is used to check if we are building in a separate output directory,
> # and if so do:
> @@ -1075,7 +1075,9 @@ prepare1: prepare2 $(version_h) $(autoksyms_h) include/generated/utsrelease.h \
> include/config/auto.conf
> $(cmd_crmodverdir)
>
> -archprepare: archheaders archscripts prepare1 scripts_basic
> +macroprepare: prepare1 archmacros
> +
> +archprepare: archheaders archscripts macroprepare scripts_basic
>
> prepare0: archprepare gcc-plugins
> $(Q)$(MAKE) $(build)=.
> @@ -1143,6 +1145,9 @@ archheaders:
> PHONY += archscripts
> archscripts:
>
> +PHONY += archmacros
> +archmacros:
> +
> PHONY += __headers
> __headers: $(version_h) scripts_basic uapi-asm-generic archheaders archscripts
> $(Q)$(MAKE) $(build)=scripts build_unifdef
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index a08e82856563..a4b90ac1629b 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -235,8 +235,8 @@ ifdef CONFIG_X86_64
> LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
> endif
>
> -# Speed up the build
> -KBUILD_CFLAGS += -pipe
> +# We cannot use -pipe flag since we give an additional .s file to the compiler
> +#KBUILD_CFLAGS += -pipe
> # Workaround for a gcc prelease that unfortunately was shipped in a suse release
> KBUILD_CFLAGS += -Wno-sign-compare
> #
> @@ -258,6 +258,13 @@ archscripts: scripts_basic
> archheaders:
> $(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all
>
> +archmacros:
> + $(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s
> +
> +ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s
> +export ASM_MACRO_FLAGS
> +KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)
> +
> ###
> # Kernel objects
>
> diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
> new file mode 100644
> index 000000000000..cfc1c7d1a6eb
> --- /dev/null
> +++ b/arch/x86/kernel/macros.S
> @@ -0,0 +1,7 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * This file includes headers whose assembly part includes macros which are
> + * commonly used. The macros are precompiled into assmebly file which is later
> + * assembled together with each compiled file.
> + */
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 86321f06461e..d7b7aadb6cd8 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -115,7 +115,9 @@ __cc-option = $(call try-run,\
>
> # Do not attempt to build with gcc plugins during cc-option tests.
> # (And this uses delayed resolution so the flags will be up to date.)
> -CC_OPTION_CFLAGS = $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS))
> +# In addition, do not include the asm macros which are built later.
> +CC_OPTION_FILTERED = $(GCC_PLUGINS_CFLAGS) $(ASM_MACRO_FLAGS)
> +CC_OPTION_CFLAGS = $(filter-out $(CC_OPTION_FILTERED),$(KBUILD_CFLAGS))
>
> # cc-option
> # Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)
> diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
> index 42c5d50f2bcc..a5b4af47987a 100644
> --- a/scripts/mod/Makefile
> +++ b/scripts/mod/Makefile
> @@ -4,6 +4,8 @@ OBJECT_FILES_NON_STANDARD := y
> hostprogs-y := modpost mk_elfconfig
> always := $(hostprogs-y) empty.o
>
> +CFLAGS_REMOVE_empty.o := $(ASM_MACRO_FLAGS)
> +
> modpost-objs := modpost.o file2alias.o sumversion.o
>
> devicetable-offsets-file := devicetable-offsets.h
> --
> 2.17.1
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Best Regards
Masahiro Yamada
Ping.
at 1:15 PM, Nadav Amit <[email protected]> wrote:
> This patch-set deals with an interesting yet stupid problem: kernel code
> that does not get inlined despite its simplicity. There are several
> causes for this behavior: "cold" attribute on __init, different function
> optimization levels; conditional constant computations based on
> __builtin_constant_p(); and finally large inline assembly blocks.
>
> This patch-set deals with the inline assembly problem. I separated these
> patches from the others (that were sent in the RFC) for easier
> inclusion. I also separated the removal of unnecessary new-lines which
> would be sent separately.
>
> The problem with inline assembly is that inline assembly is often used
> by the kernel for things that are other than code - for example,
> assembly directives and data. GCC however is oblivious to the content of
> the blocks and assumes their cost in space and time is proportional to
> the number of the perceived assembly "instruction", according to the
> number of newlines and semicolons. Alternatives, paravirt and other
> mechanisms are affected, causing code not to be inlined, and degrading
> compilation quality in general.
>
> The solution that this patch-set carries for this problem is to create
> an assembly macro, and then call it from the inline assembly block. As
> a result, the compiler sees a single "instruction" and assigns the more
> appropriate cost to the code.
>
> To avoid uglification of the code, as many noted, the macros are first
> precompiled into an assembly file, which is later assembled together
> with the C files. This also enables to avoid duplicate implementation
> that was set before for the asm and C code. This can be seen in the
> exception table changes.
>
> Overall this patch-set slightly increases the kernel size (my build was
> done using my Ubuntu 18.04 config + localyesconfig for the record):
>
> text data bss dec hex filename
> 18140829 10224724 2957312 31322865 1ddf2f1 ./vmlinux before
> 18163608 10227348 2957312 31348268 1de562c ./vmlinux after (+0.1%)
>
> The number of static functions in the image is reduced by 379, but
> actually inlining is even better, which does not always shows in these
> numbers: a function may be inlined causing the calling function not to
> be inlined.
>
> I ran some limited number of benchmarks, and in general the performance
> impact is not very notable. You can still see >10 cycles shaved off some
> syscalls that manipulate page-tables (e.g., mprotect()), in which
> paravirt caused many functions not to be inlined. In addition this
> patch-set can prevent issues such as [1], and improves code readability
> and maintainability.
>
> [1] https://patchwork.kernel.org/patch/10450037/
>
> v6->v7: * Fix context switch tracking (Ingo)
> * Fix xtensa build error (Ingo)
> * Rebase on 4.18-rc8
>
> v5->v6: * Removing more code from jump-labels (PeterZ)
> * Fix build issue on i386 (0-day, PeterZ)
>
> v4->v5: * Makefile fixes (Masahiro, Sam)
>
> v3->v4: * Changed naming of macros in 2 patches (PeterZ)
> * Minor cleanup of the paravirt patch
>
> v2->v3: * Several build issues resolved (0-day)
> * Wrong comments fix (Josh)
> * Change asm vs C order in refcount (Kees)
>
> v1->v2: * Compiling the macros into a separate .s file, improving
> readability (Linus)
> * Improving assembly formatting, applying most of the comments
> according to my judgment (Jan)
> * Adding exception-table, cpufeature and jump-labels
> * Removing new-line cleanup; to be submitted separately
>
> Cc: Masahiro Yamada <[email protected]>
> Cc: Sam Ravnborg <[email protected]>
> Cc: Alok Kataria <[email protected]>
> Cc: Christopher Li <[email protected]>
> Cc: Greg Kroah-Hartman <[email protected]>
> Cc: "H. Peter Anvin" <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Jan Beulich <[email protected]>
> Cc: Josh Poimboeuf <[email protected]>
> Cc: Juergen Gross <[email protected]>
> Cc: Kate Stewart <[email protected]>
> Cc: Kees Cook <[email protected]>
> Cc: [email protected]
> Cc: Peter Zijlstra <[email protected]>
> Cc: Philippe Ombredanne <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: [email protected]
> Cc: Linus Torvalds <[email protected]>
> Cc: [email protected]
> Cc: Chris Zankel <[email protected]>
> Cc: Max Filippov <[email protected]>
> Cc: [email protected]
>
> Nadav Amit (10):
> xtensa: defining LINKER_SCRIPT for the linker script
> Makefile: Prepare for using macros for inline asm
> x86: objtool: use asm macro for better compiler decisions
> x86: refcount: prevent gcc distortions
> x86: alternatives: macrofy locks for better inlining
> x86: bug: prevent gcc distortions
> x86: prevent inline distortion by paravirt ops
> x86: extable: use macros instead of inline assembly
> x86: cpufeature: use macros instead of inline assembly
> x86: jump-labels: use macros instead of inline assembly
>
> Makefile | 9 ++-
> arch/x86/Makefile | 11 ++-
> arch/x86/entry/calling.h | 2 +-
> arch/x86/include/asm/alternative-asm.h | 20 ++++--
> arch/x86/include/asm/alternative.h | 11 +--
> arch/x86/include/asm/asm.h | 61 +++++++---------
> arch/x86/include/asm/bug.h | 98 +++++++++++++++-----------
> arch/x86/include/asm/cpufeature.h | 82 ++++++++++++---------
> arch/x86/include/asm/jump_label.h | 77 ++++++++------------
> arch/x86/include/asm/paravirt_types.h | 56 +++++++--------
> arch/x86/include/asm/refcount.h | 74 +++++++++++--------
> arch/x86/kernel/macros.S | 16 +++++
> arch/xtensa/kernel/Makefile | 4 +-
> include/asm-generic/bug.h | 8 +--
> include/linux/compiler.h | 56 +++++++++++----
> scripts/Kbuild.include | 4 +-
> scripts/mod/Makefile | 2 +
> 17 files changed, 333 insertions(+), 258 deletions(-)
> create mode 100644 arch/x86/kernel/macros.S
>
> --
> 2.17.1
* Nadav Amit <[email protected]> wrote:
> Ping.
Masahiro Yamada noted that some Reviewed-by tags were not added - could you please double check
past mails and add them and re-send against the latest kernel?
Thanks,
Ingo
at 6:00 AM, Ingo Molnar <[email protected]> wrote:
>
> * Nadav Amit <[email protected]> wrote:
>
>> Ping.
>
> Masahiro Yamada noted that some Reviewed-by tags were not added - could you please double check
> past mails and add them and re-send against the latest kernel?
One (his) was missing. I’ll add it, rebase and send.