FTRACE's function tracer currently doesn't always work on ARM with
MODULE_PLT option enabled. If the module is loaded too far, FTRACE's
code modifier cannot cope with introduced veneers and turns the
function tracer off globally.
ARM64 already has a solution for the problem, refer to the following
patches:
arm64: ftrace: emit ftrace-mod.o contents through code
arm64: module-plts: factor out PLT generation code for ftrace
arm64: ftrace: fix !CONFIG_ARM64_MODULE_PLTS kernels
arm64: ftrace: fix building without CONFIG_MODULES
arm64: ftrace: add support for far branches to dynamic ftrace
arm64: ftrace: don't validate branch via PLT in ftrace_make_nop()
But the presented ARM variant has just a half of the footprint in terms of
the changed LoCs. It also retains the code validation-before-modification
instead of switching it off.
Changelog:
v3:
* Only extend struct dyn_arch_ftrace when ARM_MODULE_PLTS is enabled
v2:
* As suggested by Steven Rostedt, refrain from tree-wide API modification,
save module pointer in struct dyn_arch_ftrace instead (PowerPC way)
Alexander Sverdlin (2):
ARM: PLT: Move struct plt_entries definition to header
ARM: ftrace: Add MODULE_PLTS support
arch/arm/include/asm/ftrace.h | 3 +++
arch/arm/include/asm/module.h | 10 +++++++
arch/arm/kernel/ftrace.c | 62 ++++++++++++++++++++++++++++++++++++-------
arch/arm/kernel/module-plts.c | 58 ++++++++++++++++++++++++++--------------
4 files changed, 104 insertions(+), 29 deletions(-)
--
2.4.6
Teach ftrace_make_call() and ftrace_make_nop() about PLTs.
Teach PLT code about FTRACE and all its callbacks.
Otherwise the following might happen:
------------[ cut here ]------------
WARNING: CPU: 14 PID: 2265 at .../arch/arm/kernel/insn.c:14 __arm_gen_branch+0x83/0x8c()
...
Hardware name: LSI Axxia AXM55XX
[<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
[<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
[<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
[<c03218f3>] (warn_slowpath_null) from [<c03143cf>] (__arm_gen_branch+0x83/0x8c)
[<c03143cf>] (__arm_gen_branch) from [<c0314337>] (ftrace_make_nop+0xf/0x24)
[<c0314337>] (ftrace_make_nop) from [<c038ebcb>] (ftrace_process_locs+0x27b/0x3e8)
[<c038ebcb>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
[<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
[<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
---[ end trace e1b64ced7a89adcc ]---
------------[ cut here ]------------
WARNING: CPU: 14 PID: 2265 at .../kernel/trace/ftrace.c:1979 ftrace_bug+0x1b1/0x234()
...
Hardware name: LSI Axxia AXM55XX
[<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
[<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
[<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
[<c03218f3>] (warn_slowpath_null) from [<c038e87d>] (ftrace_bug+0x1b1/0x234)
[<c038e87d>] (ftrace_bug) from [<c038ebd5>] (ftrace_process_locs+0x285/0x3e8)
[<c038ebd5>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
[<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
[<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
---[ end trace e1b64ced7a89adcd ]---
ftrace failed to modify [<e9ef7006>] 0xe9ef7006
actual: 02:f0:3b:fa
ftrace record flags: 0
(0) expected tramp: c0314265
Signed-off-by: Alexander Sverdlin <[email protected]>
---
arch/arm/include/asm/ftrace.h | 3 +++
arch/arm/include/asm/module.h | 1 +
arch/arm/kernel/ftrace.c | 62 ++++++++++++++++++++++++++++++++++++-------
arch/arm/kernel/module-plts.c | 53 +++++++++++++++++++++++++++---------
4 files changed, 97 insertions(+), 22 deletions(-)
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 9e842ff..faeb6b1 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -19,6 +19,9 @@ struct dyn_arch_ftrace {
#ifdef CONFIG_OLD_MCOUNT
bool old_mcount;
#endif
+#ifdef CONFIG_ARM_MODULE_PLTS
+ struct module *mod;
+#endif
};
static inline unsigned long ftrace_call_adjust(unsigned long addr)
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index 6996405..e3d7a51 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -30,6 +30,7 @@ struct plt_entries {
struct mod_plt_sec {
struct elf32_shdr *plt;
+ struct plt_entries *plt_ent;
int plt_count;
};
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 5617932..b55355f 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -98,6 +98,19 @@ int ftrace_arch_code_modify_post_process(void)
static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
{
+ s32 offset = addr - pc;
+ s32 blim = 0xfe000008;
+ s32 flim = 0x02000004;
+
+ if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
+ blim = 0xff000004;
+ flim = 0x01000002;
+ }
+
+ if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
+ (offset < blim || offset > flim))
+ return 0;
+
return arm_gen_branch_link(pc, addr);
}
@@ -166,10 +179,22 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long new, old;
unsigned long ip = rec->ip;
+ unsigned long aaddr = adjust_address(rec, addr);
old = ftrace_nop_replace(rec);
- new = ftrace_call_replace(ip, adjust_address(rec, addr));
+ new = ftrace_call_replace(ip, aaddr);
+
+#ifdef CONFIG_ARM_MODULE_PLTS
+ if (!new) {
+ struct module *mod = rec->arch.mod;
+
+ if (mod) {
+ aaddr = get_module_plt(mod, ip, aaddr);
+ new = ftrace_call_replace(ip, aaddr);
+ }
+ }
+#endif
return ftrace_modify_code(rec->ip, old, new, true);
}
@@ -199,20 +224,39 @@ int ftrace_make_nop(struct module *mod,
unsigned long new;
int ret;
- old = ftrace_call_replace(ip, adjust_address(rec, addr));
- new = ftrace_nop_replace(rec);
- ret = ftrace_modify_code(ip, old, new, true);
+#ifdef CONFIG_ARM_MODULE_PLTS
+ /* mod is only supplied during module loading */
+ if (!mod)
+ mod = rec->arch.mod;
+ else
+ rec->arch.mod = mod;
+#endif
-#ifdef CONFIG_OLD_MCOUNT
- if (ret == -EINVAL && addr == MCOUNT_ADDR) {
- rec->arch.old_mcount = true;
+ for (;;) {
+ unsigned long aaddr = adjust_address(rec, addr);
+
+ old = ftrace_call_replace(ip, aaddr);
+
+#ifdef CONFIG_ARM_MODULE_PLTS
+ if (!old && mod) {
+ aaddr = get_module_plt(mod, ip, aaddr);
+ old = ftrace_call_replace(ip, aaddr);
+ }
+#endif
- old = ftrace_call_replace(ip, adjust_address(rec, addr));
new = ftrace_nop_replace(rec);
ret = ftrace_modify_code(ip, old, new, true);
- }
+
+#ifdef CONFIG_OLD_MCOUNT
+ if (ret == -EINVAL && !rec->arch.old_mcount) {
+ rec->arch.old_mcount = true;
+ continue;
+ }
#endif
+ break;
+ }
+
return ret;
}
diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
index f272711..a216256 100644
--- a/arch/arm/kernel/module-plts.c
+++ b/arch/arm/kernel/module-plts.c
@@ -7,6 +7,7 @@
*/
#include <linux/elf.h>
+#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sort.h>
@@ -22,6 +23,15 @@
(PLT_ENT_STRIDE - 8))
#endif
+static u32 fixed_plts[] = {
+ FTRACE_ADDR,
+ MCOUNT_ADDR,
+#ifdef CONFIG_OLD_MCOUNT
+ (unsigned long)ftrace_caller_old,
+ (unsigned long)mcount,
+#endif
+};
+
static bool in_init(const struct module *mod, unsigned long loc)
{
return loc - (u32)mod->init_layout.base < mod->init_layout.size;
@@ -31,26 +41,43 @@ u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
{
struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
&mod->arch.init;
+ int idx;
+ struct plt_entries *plt;
+
+ /* Pre-allocate entries in the first plt */
+ if (!pltsec->plt_count) {
+ plt = (struct plt_entries *)pltsec->plt->sh_addr;
+ for (idx = 0; idx < ARRAY_SIZE(plt->ldr); ++idx)
+ plt->ldr[idx] = PLT_ENT_LDR;
+ memcpy(plt->lit, fixed_plts, sizeof(fixed_plts));
+ pltsec->plt_count = ARRAY_SIZE(fixed_plts);
+ /*
+ * cache the address,
+ * ELF header is available only during module load
+ */
+ pltsec->plt_ent = plt;
+ }
+ plt = pltsec->plt_ent;
- struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
- int idx = 0;
+ idx = ARRAY_SIZE(fixed_plts);
+ while (idx)
+ if (plt->lit[--idx] == val)
+ return (u32)&plt->ldr[idx];
/*
* Look for an existing entry pointing to 'val'. Given that the
* relocations are sorted, this will be the last entry we allocated.
* (if one exists).
*/
- if (pltsec->plt_count > 0) {
- plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT;
- idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT;
+ plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT;
+ idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT;
- if (plt->lit[idx] == val)
- return (u32)&plt->ldr[idx];
+ if (plt->lit[idx] == val)
+ return (u32)&plt->ldr[idx];
- idx = (idx + 1) % PLT_ENT_COUNT;
- if (!idx)
- plt++;
- }
+ idx = (idx + 1) % PLT_ENT_COUNT;
+ if (!idx)
+ plt++;
pltsec->plt_count++;
BUG_ON(pltsec->plt_count * PLT_ENT_SIZE > pltsec->plt->sh_size);
@@ -182,8 +209,8 @@ static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod)
{
- unsigned long core_plts = 0;
- unsigned long init_plts = 0;
+ unsigned long core_plts = ARRAY_SIZE(fixed_plts);
+ unsigned long init_plts = ARRAY_SIZE(fixed_plts);
Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
Elf32_Sym *syms = NULL;
--
2.4.6
No functional change, later it will be re-used in several files.
Change-Id: Icfa32669b3582d713b3ad680c25620d3d4844bdd
Signed-off-by: Alexander Sverdlin <[email protected]>
---
arch/arm/include/asm/module.h | 9 +++++++++
arch/arm/kernel/module-plts.c | 9 ---------
2 files changed, 9 insertions(+), 9 deletions(-)
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index 89ad059..6996405 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -19,6 +19,15 @@ enum {
};
#endif
+#define PLT_ENT_STRIDE L1_CACHE_BYTES
+#define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32))
+#define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT)
+
+struct plt_entries {
+ u32 ldr[PLT_ENT_COUNT];
+ u32 lit[PLT_ENT_COUNT];
+};
+
struct mod_plt_sec {
struct elf32_shdr *plt;
int plt_count;
diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
index 3d0c2e4..f272711 100644
--- a/arch/arm/kernel/module-plts.c
+++ b/arch/arm/kernel/module-plts.c
@@ -14,10 +14,6 @@
#include <asm/cache.h>
#include <asm/opcodes.h>
-#define PLT_ENT_STRIDE L1_CACHE_BYTES
-#define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32))
-#define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT)
-
#ifdef CONFIG_THUMB2_KERNEL
#define PLT_ENT_LDR __opcode_to_mem_thumb32(0xf8dff000 | \
(PLT_ENT_STRIDE - 4))
@@ -26,11 +22,6 @@
(PLT_ENT_STRIDE - 8))
#endif
-struct plt_entries {
- u32 ldr[PLT_ENT_COUNT];
- u32 lit[PLT_ENT_COUNT];
-};
-
static bool in_init(const struct module *mod, unsigned long loc)
{
return loc - (u32)mod->init_layout.base < mod->init_layout.size;
--
2.4.6
Hi Alexander,
On 9 March 2018 at 08:41, Alexander Sverdlin
<[email protected]> wrote:
> Teach ftrace_make_call() and ftrace_make_nop() about PLTs.
> Teach PLT code about FTRACE and all its callbacks.
> Otherwise the following might happen:
>
> ------------[ cut here ]------------
> WARNING: CPU: 14 PID: 2265 at .../arch/arm/kernel/insn.c:14 __arm_gen_branch+0x83/0x8c()
> ...
> Hardware name: LSI Axxia AXM55XX
> [<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
> [<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
> [<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
> [<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
> [<c03218f3>] (warn_slowpath_null) from [<c03143cf>] (__arm_gen_branch+0x83/0x8c)
> [<c03143cf>] (__arm_gen_branch) from [<c0314337>] (ftrace_make_nop+0xf/0x24)
> [<c0314337>] (ftrace_make_nop) from [<c038ebcb>] (ftrace_process_locs+0x27b/0x3e8)
> [<c038ebcb>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
> [<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
> [<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
> ---[ end trace e1b64ced7a89adcc ]---
> ------------[ cut here ]------------
> WARNING: CPU: 14 PID: 2265 at .../kernel/trace/ftrace.c:1979 ftrace_bug+0x1b1/0x234()
> ...
> Hardware name: LSI Axxia AXM55XX
> [<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
> [<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
> [<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
> [<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
> [<c03218f3>] (warn_slowpath_null) from [<c038e87d>] (ftrace_bug+0x1b1/0x234)
> [<c038e87d>] (ftrace_bug) from [<c038ebd5>] (ftrace_process_locs+0x285/0x3e8)
> [<c038ebd5>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
> [<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
> [<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
> ---[ end trace e1b64ced7a89adcd ]---
> ftrace failed to modify [<e9ef7006>] 0xe9ef7006
> actual: 02:f0:3b:fa
> ftrace record flags: 0
> (0) expected tramp: c0314265
>
> Signed-off-by: Alexander Sverdlin <[email protected]>
> ---
> arch/arm/include/asm/ftrace.h | 3 +++
> arch/arm/include/asm/module.h | 1 +
> arch/arm/kernel/ftrace.c | 62 ++++++++++++++++++++++++++++++++++++-------
> arch/arm/kernel/module-plts.c | 53 +++++++++++++++++++++++++++---------
> 4 files changed, 97 insertions(+), 22 deletions(-)
>
> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> index 9e842ff..faeb6b1 100644
> --- a/arch/arm/include/asm/ftrace.h
> +++ b/arch/arm/include/asm/ftrace.h
> @@ -19,6 +19,9 @@ struct dyn_arch_ftrace {
> #ifdef CONFIG_OLD_MCOUNT
> bool old_mcount;
> #endif
> +#ifdef CONFIG_ARM_MODULE_PLTS
> + struct module *mod;
> +#endif
> };
>
> static inline unsigned long ftrace_call_adjust(unsigned long addr)
> diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
> index 6996405..e3d7a51 100644
> --- a/arch/arm/include/asm/module.h
> +++ b/arch/arm/include/asm/module.h
> @@ -30,6 +30,7 @@ struct plt_entries {
>
> struct mod_plt_sec {
> struct elf32_shdr *plt;
> + struct plt_entries *plt_ent;
> int plt_count;
> };
>
> diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
> index 5617932..b55355f 100644
> --- a/arch/arm/kernel/ftrace.c
> +++ b/arch/arm/kernel/ftrace.c
> @@ -98,6 +98,19 @@ int ftrace_arch_code_modify_post_process(void)
>
> static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
> {
> + s32 offset = addr - pc;
> + s32 blim = 0xfe000008;
> + s32 flim = 0x02000004;
> +
> + if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
> + blim = 0xff000004;
> + flim = 0x01000002;
> + }
> +
> + if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
> + (offset < blim || offset > flim))
> + return 0;
> +
> return arm_gen_branch_link(pc, addr);
> }
>
> @@ -166,10 +179,22 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> {
> unsigned long new, old;
> unsigned long ip = rec->ip;
> + unsigned long aaddr = adjust_address(rec, addr);
>
> old = ftrace_nop_replace(rec);
>
> - new = ftrace_call_replace(ip, adjust_address(rec, addr));
> + new = ftrace_call_replace(ip, aaddr);
> +
> +#ifdef CONFIG_ARM_MODULE_PLTS
> + if (!new) {
> + struct module *mod = rec->arch.mod;
> +
> + if (mod) {
> + aaddr = get_module_plt(mod, ip, aaddr);
> + new = ftrace_call_replace(ip, aaddr);
> + }
> + }
> +#endif
>
> return ftrace_modify_code(rec->ip, old, new, true);
> }
> @@ -199,20 +224,39 @@ int ftrace_make_nop(struct module *mod,
> unsigned long new;
> int ret;
>
> - old = ftrace_call_replace(ip, adjust_address(rec, addr));
> - new = ftrace_nop_replace(rec);
> - ret = ftrace_modify_code(ip, old, new, true);
> +#ifdef CONFIG_ARM_MODULE_PLTS
> + /* mod is only supplied during module loading */
> + if (!mod)
> + mod = rec->arch.mod;
> + else
> + rec->arch.mod = mod;
> +#endif
>
> -#ifdef CONFIG_OLD_MCOUNT
> - if (ret == -EINVAL && addr == MCOUNT_ADDR) {
> - rec->arch.old_mcount = true;
> + for (;;) {
> + unsigned long aaddr = adjust_address(rec, addr);
> +
> + old = ftrace_call_replace(ip, aaddr);
> +
> +#ifdef CONFIG_ARM_MODULE_PLTS
> + if (!old && mod) {
> + aaddr = get_module_plt(mod, ip, aaddr);
> + old = ftrace_call_replace(ip, aaddr);
> + }
> +#endif
>
> - old = ftrace_call_replace(ip, adjust_address(rec, addr));
> new = ftrace_nop_replace(rec);
> ret = ftrace_modify_code(ip, old, new, true);
> - }
> +
> +#ifdef CONFIG_OLD_MCOUNT
> + if (ret == -EINVAL && !rec->arch.old_mcount) {
> + rec->arch.old_mcount = true;
> + continue;
> + }
> #endif
>
> + break;
> + }
> +
> return ret;
> }
>
> diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
> index f272711..a216256 100644
> --- a/arch/arm/kernel/module-plts.c
> +++ b/arch/arm/kernel/module-plts.c
> @@ -7,6 +7,7 @@
> */
>
> #include <linux/elf.h>
> +#include <linux/ftrace.h>
> #include <linux/kernel.h>
> #include <linux/module.h>
> #include <linux/sort.h>
> @@ -22,6 +23,15 @@
> (PLT_ENT_STRIDE - 8))
> #endif
>
> +static u32 fixed_plts[] = {
> + FTRACE_ADDR,
> + MCOUNT_ADDR,
> +#ifdef CONFIG_OLD_MCOUNT
> + (unsigned long)ftrace_caller_old,
> + (unsigned long)mcount,
> +#endif
> +};
> +
Do we need this stuff in the PLT loader if ftrace is disabled?
> static bool in_init(const struct module *mod, unsigned long loc)
> {
> return loc - (u32)mod->init_layout.base < mod->init_layout.size;
> @@ -31,26 +41,43 @@ u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
> {
> struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
> &mod->arch.init;
> + int idx;
> + struct plt_entries *plt;
> +
> + /* Pre-allocate entries in the first plt */
> + if (!pltsec->plt_count) {
> + plt = (struct plt_entries *)pltsec->plt->sh_addr;
> + for (idx = 0; idx < ARRAY_SIZE(plt->ldr); ++idx)
> + plt->ldr[idx] = PLT_ENT_LDR;
> + memcpy(plt->lit, fixed_plts, sizeof(fixed_plts));
> + pltsec->plt_count = ARRAY_SIZE(fixed_plts);
> + /*
> + * cache the address,
> + * ELF header is available only during module load
> + */
> + pltsec->plt_ent = plt;
> + }
> + plt = pltsec->plt_ent;
>
> - struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
> - int idx = 0;
> + idx = ARRAY_SIZE(fixed_plts);
> + while (idx)
> + if (plt->lit[--idx] == val)
> + return (u32)&plt->ldr[idx];
>
Same here.
> /*
> * Look for an existing entry pointing to 'val'. Given that the
> * relocations are sorted, this will be the last entry we allocated.
> * (if one exists).
> */
> - if (pltsec->plt_count > 0) {
> - plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT;
> - idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT;
> + plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT;
> + idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT;
>
> - if (plt->lit[idx] == val)
> - return (u32)&plt->ldr[idx];
> + if (plt->lit[idx] == val)
> + return (u32)&plt->ldr[idx];
>
> - idx = (idx + 1) % PLT_ENT_COUNT;
> - if (!idx)
> - plt++;
> - }
> + idx = (idx + 1) % PLT_ENT_COUNT;
> + if (!idx)
> + plt++;
>
> pltsec->plt_count++;
> BUG_ON(pltsec->plt_count * PLT_ENT_SIZE > pltsec->plt->sh_size);
> @@ -182,8 +209,8 @@ static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
> int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
> char *secstrings, struct module *mod)
> {
> - unsigned long core_plts = 0;
> - unsigned long init_plts = 0;
> + unsigned long core_plts = ARRAY_SIZE(fixed_plts);
> + unsigned long init_plts = ARRAY_SIZE(fixed_plts);
> Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
> Elf32_Sym *syms = NULL;
>
> --
> 2.4.6
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Hello Ard!
On 09/03/18 09:50, Ard Biesheuvel wrote:
>> +static u32 fixed_plts[] = {
>> + FTRACE_ADDR,
>> + MCOUNT_ADDR,
>> +#ifdef CONFIG_OLD_MCOUNT
>> + (unsigned long)ftrace_caller_old,
>> + (unsigned long)mcount,
>> +#endif
>> +};
>> +
> Do we need this stuff in the PLT loader if ftrace is disabled?
You are right, it probably would not even build w/o FTRACE.
I'll fix it, thanks for looking into this!
>> static bool in_init(const struct module *mod, unsigned long loc)
>> {
>> return loc - (u32)mod->init_layout.base < mod->init_layout.size;
>> @@ -31,26 +41,43 @@ u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
>> {
>> struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
>> &mod->arch.init;
>> + int idx;
>> + struct plt_entries *plt;
>> +
>> + /* Pre-allocate entries in the first plt */
>> + if (!pltsec->plt_count) {
>> + plt = (struct plt_entries *)pltsec->plt->sh_addr;
>> + for (idx = 0; idx < ARRAY_SIZE(plt->ldr); ++idx)
>> + plt->ldr[idx] = PLT_ENT_LDR;
>> + memcpy(plt->lit, fixed_plts, sizeof(fixed_plts));
>> + pltsec->plt_count = ARRAY_SIZE(fixed_plts);
>> + /*
>> + * cache the address,
>> + * ELF header is available only during module load
>> + */
>> + pltsec->plt_ent = plt;
>> + }
>> + plt = pltsec->plt_ent;
>>
>> - struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
>> - int idx = 0;
>> + idx = ARRAY_SIZE(fixed_plts);
>> + while (idx)
>> + if (plt->lit[--idx] == val)
>> + return (u32)&plt->ldr[idx];
>>
> Same here.
--
Best regards,
Alexander Sverdlin.
On 9 March 2018 at 08:54, Alexander Sverdlin
<[email protected]> wrote:
> Hello Ard!
>
> On 09/03/18 09:50, Ard Biesheuvel wrote:
>>> +static u32 fixed_plts[] = {
>>> + FTRACE_ADDR,
>>> + MCOUNT_ADDR,
>>> +#ifdef CONFIG_OLD_MCOUNT
>>> + (unsigned long)ftrace_caller_old,
>>> + (unsigned long)mcount,
>>> +#endif
>>> +};
>>> +
>> Do we need this stuff in the PLT loader if ftrace is disabled?
>
> You are right, it probably would not even build w/o FTRACE.
> I'll fix it, thanks for looking into this!
>
Also, perhaps you can make the array const (after you put #ifdef's
around all entries)
>>> static bool in_init(const struct module *mod, unsigned long loc)
>>> {
>>> return loc - (u32)mod->init_layout.base < mod->init_layout.size;
>>> @@ -31,26 +41,43 @@ u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
>>> {
>>> struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
>>> &mod->arch.init;
>>> + int idx;
>>> + struct plt_entries *plt;
>>> +
>>> + /* Pre-allocate entries in the first plt */
>>> + if (!pltsec->plt_count) {
>>> + plt = (struct plt_entries *)pltsec->plt->sh_addr;
>>> + for (idx = 0; idx < ARRAY_SIZE(plt->ldr); ++idx)
>>> + plt->ldr[idx] = PLT_ENT_LDR;
>>> + memcpy(plt->lit, fixed_plts, sizeof(fixed_plts));
>>> + pltsec->plt_count = ARRAY_SIZE(fixed_plts);
>>> + /*
>>> + * cache the address,
>>> + * ELF header is available only during module load
>>> + */
>>> + pltsec->plt_ent = plt;
>>> + }
>>> + plt = pltsec->plt_ent;
>>>
>>> - struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
>>> - int idx = 0;
>>> + idx = ARRAY_SIZE(fixed_plts);
>>> + while (idx)
>>> + if (plt->lit[--idx] == val)
>>> + return (u32)&plt->ldr[idx];
>>>
... and put all this handling in a helper function that only gets
called if ARRAY_SIZE() > 0
AFAICT, that should allow you to leave the rest unchanged.