Make objtool annotations arch assembler independent. Would be nice if this goes
via objtool tree. I have further patches which depend on that.
Vasily Gorbik (2):
compiler.h: Avoid using inline asm operand modifiers
instrumentation.h: Avoid using inline asm operand modifiers
include/linux/compiler.h | 22 ++++++++++++++--------
include/linux/instrumentation.h | 20 ++++++++++++--------
2 files changed, 26 insertions(+), 16 deletions(-)
--
2.25.4
The expansion of annotate_reachable/annotate_unreachable on s390 will
result in a compiler error if the __COUNTER__ value is high enough.
For example with "i" (154) the "%c0" operand of annotate_reachable
will be expanded to -102:
-102:
.pushsection .discard.reachable
.long -102b - .
.popsection
This is a quirk of the gcc backend for s390, it interprets the %c0
as a signed byte value. Avoid using operand modifiers in this case
by simply converting __COUNTER__ to string, with the same result,
but in an arch assembler independent way.
Signed-off-by: Vasily Gorbik <[email protected]>
---
include/linux/compiler.h | 22 ++++++++++++++--------
1 file changed, 14 insertions(+), 8 deletions(-)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index df5b405e6305..77047904cf70 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -115,18 +115,24 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
* The __COUNTER__ based labels are a hack to make each instance of the macros
* unique, to convince GCC not to merge duplicate inline asm statements.
*/
-#define annotate_reachable() ({ \
- asm volatile("%c0:\n\t" \
+#define __stringify_label(n) #n
+
+#define __annotate_reachable(c) ({ \
+ asm volatile(__stringify_label(c) ":\n\t" \
".pushsection .discard.reachable\n\t" \
- ".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__COUNTER__)); \
+ ".long " __stringify_label(c) "b - .\n\t" \
+ ".popsection\n\t"); \
})
-#define annotate_unreachable() ({ \
- asm volatile("%c0:\n\t" \
+#define annotate_reachable() __annotate_reachable(__COUNTER__)
+
+#define __annotate_unreachable(c) ({ \
+ asm volatile(__stringify_label(c) ":\n\t" \
".pushsection .discard.unreachable\n\t" \
- ".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__COUNTER__)); \
+ ".long " __stringify_label(c) "b - .\n\t" \
+ ".popsection\n\t"); \
})
+#define annotate_unreachable() __annotate_unreachable(__COUNTER__)
+
#define ASM_UNREACHABLE \
"999:\n\t" \
".pushsection .discard.unreachable\n\t" \
--
2.25.4
On Wed, May 19, 2021 at 03:03:02PM +0200, Vasily Gorbik wrote:
> Make objtool annotations arch assembler independent. Would be nice if this goes
> via objtool tree. I have further patches which depend on that.
>
> Vasily Gorbik (2):
> compiler.h: Avoid using inline asm operand modifiers
> instrumentation.h: Avoid using inline asm operand modifiers
>
> include/linux/compiler.h | 22 ++++++++++++++--------
> include/linux/instrumentation.h | 20 ++++++++++++--------
> 2 files changed, 26 insertions(+), 16 deletions(-)
Thanks Vasily, looks good to me. Running it through some testing.
--
Josh
The expansion of instrumentation_begin/instrumentation_end on s390 will
result in a compiler error if the __COUNTER__ value is high enough.
For example with "i" (154) the "%c0" operand of annotate_reachable
will be expanded to -102:
-102:
.pushsection .discard.instr_begin
.long -102b - .
.popsection
This is a quirk of the gcc backend for s390, it interprets the %c0
as a signed byte value. Avoid using operand modifiers in this case
by simply converting __COUNTER__ to string, with the same result,
but in an arch assembler independent way.
Signed-off-by: Vasily Gorbik <[email protected]>
---
include/linux/instrumentation.h | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/include/linux/instrumentation.h b/include/linux/instrumentation.h
index 93e2ad67fc10..fa2cd8c63dcc 100644
--- a/include/linux/instrumentation.h
+++ b/include/linux/instrumentation.h
@@ -4,13 +4,16 @@
#if defined(CONFIG_DEBUG_ENTRY) && defined(CONFIG_STACK_VALIDATION)
+#include <linux/stringify.h>
+
/* Begin/end of an instrumentation safe region */
-#define instrumentation_begin() ({ \
- asm volatile("%c0: nop\n\t" \
+#define __instrumentation_begin(c) ({ \
+ asm volatile(__stringify(c) ": nop\n\t" \
".pushsection .discard.instr_begin\n\t" \
- ".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__COUNTER__)); \
+ ".long " __stringify(c) "b - .\n\t" \
+ ".popsection\n\t"); \
})
+#define instrumentation_begin() __instrumentation_begin(__COUNTER__)
/*
* Because instrumentation_{begin,end}() can nest, objtool validation considers
@@ -43,12 +46,13 @@
* To avoid this, have _end() be a NOP instruction, this ensures it will be
* part of the condition block and does not escape.
*/
-#define instrumentation_end() ({ \
- asm volatile("%c0: nop\n\t" \
+#define __instrumentation_end(c) ({ \
+ asm volatile(__stringify(c) ": nop\n\t" \
".pushsection .discard.instr_end\n\t" \
- ".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__COUNTER__)); \
+ ".long " __stringify(c) "b - .\n\t" \
+ ".popsection\n\t"); \
})
+#define instrumentation_end() __instrumentation_end(__COUNTER__)
#else
# define instrumentation_begin() do { } while(0)
# define instrumentation_end() do { } while(0)
--
2.25.4
On Wed, May 19, 2021 at 03:03:08PM +0200, Vasily Gorbik wrote:
> The expansion of annotate_reachable/annotate_unreachable on s390 will
> result in a compiler error if the __COUNTER__ value is high enough.
> For example with "i" (154) the "%c0" operand of annotate_reachable
> will be expanded to -102:
>
> -102:
> .pushsection .discard.reachable
> .long -102b - .
> .popsection
>
> This is a quirk of the gcc backend for s390, it interprets the %c0
> as a signed byte value. Avoid using operand modifiers in this case
> by simply converting __COUNTER__ to string, with the same result,
> but in an arch assembler independent way.
>
> Signed-off-by: Vasily Gorbik <[email protected]>
Hi Vasily,
This patch causes these macros to break with Clang and
CONFIG_TRACE_BRANCH_PROFILING.
I get a lot of warnings like
arch/x86/kernel/traps.o: warning: objtool: handle_xfd_event()+0x134: unreachable instruction
Without an asm input, 'volatile' is ignored for some reason and Clang
feels free to move the reachable() annotation away from its intended
location.
I wonder if we could go back to the original approach of providing
__COUNTER__ as an input to the asm, but then mask it to < 128.
Does this work on s390?
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 3d5af56337bd..42935500a712 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -115,24 +115,18 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
* The __COUNTER__ based labels are a hack to make each instance of the macros
* unique, to convince GCC not to merge duplicate inline asm statements.
*/
-#define __stringify_label(n) #n
-
-#define __annotate_reachable(c) ({ \
- asm volatile(__stringify_label(c) ":\n\t" \
+#define annotate_reachable() ({ \
+ asm volatile("%c0:\n\t" \
".pushsection .discard.reachable\n\t" \
- ".long " __stringify_label(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".long %c0b - .\n\t" \
+ ".popsection\n\t" : : "i" (__COUNTER__ & 0x7f)); \
})
-#define annotate_reachable() __annotate_reachable(__COUNTER__)
-
-#define __annotate_unreachable(c) ({ \
- asm volatile(__stringify_label(c) ":\n\t" \
+#define annotate_unreachable() ({ \
+ asm volatile("%c0:\n\t" \
".pushsection .discard.unreachable\n\t" \
- ".long " __stringify_label(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".long %c0b - .\n\t" \
+ ".popsection\n\t" : : "i" (__COUNTER__ & 0x7f)); \
})
-#define annotate_unreachable() __annotate_unreachable(__COUNTER__)
-
#define ASM_UNREACHABLE \
"999:\n\t" \
".pushsection .discard.unreachable\n\t" \
On Fri, Nov 05, 2021 at 09:54:18AM -0700, Josh Poimboeuf wrote:
> On Wed, May 19, 2021 at 03:03:08PM +0200, Vasily Gorbik wrote:
> > The expansion of annotate_reachable/annotate_unreachable on s390 will
> > result in a compiler error if the __COUNTER__ value is high enough.
> > For example with "i" (154) the "%c0" operand of annotate_reachable
> > will be expanded to -102:
> >
> > -102:
> > .pushsection .discard.reachable
> > .long -102b - .
> > .popsection
> >
> > This is a quirk of the gcc backend for s390, it interprets the %c0
> > as a signed byte value. Avoid using operand modifiers in this case
> > by simply converting __COUNTER__ to string, with the same result,
> > but in an arch assembler independent way.
> >
> > Signed-off-by: Vasily Gorbik <[email protected]>
>
> This patch causes these macros to break with Clang and
> CONFIG_TRACE_BRANCH_PROFILING.
>
> I get a lot of warnings like
>
> arch/x86/kernel/traps.o: warning: objtool: handle_xfd_event()+0x134: unreachable instruction
>
> Without an asm input, 'volatile' is ignored for some reason and Clang
> feels free to move the reachable() annotation away from its intended
> location.
>
> I wonder if we could go back to the original approach of providing
> __COUNTER__ as an input to the asm, but then mask it to < 128.
>
> Does this work on s390?
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 3d5af56337bd..42935500a712 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -115,24 +115,18 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> * The __COUNTER__ based labels are a hack to make each instance of the macros
> * unique, to convince GCC not to merge duplicate inline asm statements.
> */
> -#define __stringify_label(n) #n
> -
> -#define __annotate_reachable(c) ({ \
> - asm volatile(__stringify_label(c) ":\n\t" \
> +#define annotate_reachable() ({ \
> + asm volatile("%c0:\n\t" \
> ".pushsection .discard.reachable\n\t" \
> - ".long " __stringify_label(c) "b - .\n\t" \
> - ".popsection\n\t"); \
> + ".long %c0b - .\n\t" \
> + ".popsection\n\t" : : "i" (__COUNTER__ & 0x7f)); \
> })
hm, could we just add asm input back and not use it? and keep
__stringify_label(c) as is? would that work as well?
On Mon, Nov 08, 2021 at 04:40:38PM +0100, Vasily Gorbik wrote:
> > Does this work on s390?
> >
> > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > index 3d5af56337bd..42935500a712 100644
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -115,24 +115,18 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> > * The __COUNTER__ based labels are a hack to make each instance of the macros
> > * unique, to convince GCC not to merge duplicate inline asm statements.
> > */
> > -#define __stringify_label(n) #n
> > -
> > -#define __annotate_reachable(c) ({ \
> > - asm volatile(__stringify_label(c) ":\n\t" \
> > +#define annotate_reachable() ({ \
> > + asm volatile("%c0:\n\t" \
> > ".pushsection .discard.reachable\n\t" \
> > - ".long " __stringify_label(c) "b - .\n\t" \
> > - ".popsection\n\t"); \
> > + ".long %c0b - .\n\t" \
> > + ".popsection\n\t" : : "i" (__COUNTER__ & 0x7f)); \
> > })
>
> hm, could we just add asm input back and not use it? and keep
> __stringify_label(c) as is? would that work as well?
Yeah, that seems to work:
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 3d5af56337bd..429dcebe2b99 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -121,7 +121,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
asm volatile(__stringify_label(c) ":\n\t" \
".pushsection .discard.reachable\n\t" \
".long " __stringify_label(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".popsection\n\t" : : "i" (c)); \
})
#define annotate_reachable() __annotate_reachable(__COUNTER__)
@@ -129,7 +129,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
asm volatile(__stringify_label(c) ":\n\t" \
".pushsection .discard.unreachable\n\t" \
".long " __stringify_label(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".popsection\n\t" : : "i" (c)); \
})
#define annotate_unreachable() __annotate_unreachable(__COUNTER__)
diff --git a/include/linux/instrumentation.h b/include/linux/instrumentation.h
index fa2cd8c63dcc..24359b4a9605 100644
--- a/include/linux/instrumentation.h
+++ b/include/linux/instrumentation.h
@@ -11,7 +11,7 @@
asm volatile(__stringify(c) ": nop\n\t" \
".pushsection .discard.instr_begin\n\t" \
".long " __stringify(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".popsection\n\t" : : "i" (c)); \
})
#define instrumentation_begin() __instrumentation_begin(__COUNTER__)
@@ -50,7 +50,7 @@
asm volatile(__stringify(c) ": nop\n\t" \
".pushsection .discard.instr_end\n\t" \
".long " __stringify(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".popsection\n\t" : : "i" (c)); \
})
#define instrumentation_end() __instrumentation_end(__COUNTER__)
#else
From: Vasily Gorbik
> Sent: 08 November 2021 15:41
>
> On Fri, Nov 05, 2021 at 09:54:18AM -0700, Josh Poimboeuf wrote:
> > On Wed, May 19, 2021 at 03:03:08PM +0200, Vasily Gorbik wrote:
> > > The expansion of annotate_reachable/annotate_unreachable on s390 will
> > > result in a compiler error if the __COUNTER__ value is high enough.
...
> > I wonder if we could go back to the original approach of providing
> > __COUNTER__ as an input to the asm, but then mask it to < 128.
...
> > * The __COUNTER__ based labels are a hack to make each instance of the macros
> > * unique, to convince GCC not to merge duplicate inline asm statements.
I've used asm comments get the same effect.
Annoyingly there isn't a standard comment delimiter.
I think you can just use a .equ (or .set) directive (to assign a value)
rather than putting a value into a 'to be discarded' section.
David
-
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