ARM: ftrace fixes and cleanups
Subsystems (2)
cover ARM: ftrace fixes and cleanups
This series addresses a number of issues in the ARM support code for ftrace, mostly related to Thumb2 but affecting other configurations as well.
Ard Biesheuvel (8):
ARM: ftrace: ensure that ADR take Thumb bit into account
ARM: ftrace: use ADD not POP to counter PUSH at entry
ARM: ftrace: use trampolines to keep .init.text in branching range
ARM: ftrace: avoid redundant loads or clobbering IP
ARM: ftrace: avoid unnecessary literal loads
ARM: ftrace: enable HAVE_FUNCTION_GRAPH_FP_TEST
ARM: unwind: track location of LR value in stack frame
ARM: ftrace: enable the graph tracer with the EABI unwinder
arch/arm/Kconfig | 2 +- arch/arm/Kconfig.debug | 2 +- arch/arm/include/asm/ftrace.h | 20 +-- arch/arm/include/asm/stacktrace.h | 2 + arch/arm/kernel/Makefile | 6 +- arch/arm/kernel/entry-ftrace.S | 128 +++++++++++--------- arch/arm/kernel/ftrace.c | 47 ++++++- arch/arm/kernel/unwind.c | 7 +- 8 files changed, 125 insertions(+), 89 deletions(-)
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2.30.2 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
PATCH 1/8 ARM: ftrace: ensure that ADR take Thumb bit into account
Using ADR to take the address of 'ftrace_stub' via a local label produces an address that has the Thumb bit cleared, which means the subsequent comparison is guaranteed to fail. Instead, use the badr macro, which forces the Thumb bit to be set.
--- arch/arm/kernel/entry-ftrace.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
arch/arm/kernel/entry-ftrace.S +1 -1
@@ -40,7 +40,7 @@ mcount_enter ldr r0, =ftrace_trace_function ldr r2, [r0] - adr r0, .Lftrace_stub + badr r0, .Lftrace_stub cmp r0, r2 bne 1f
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2.30.2 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Re: [PATCH 1/8] ARM: ftrace: ensure that ADR take Thumb bit into account
Quoted 8 lines · Ard Biesheuvel
Using ADR to take the address of '
ftrace_stub' via a local label produces an address that has the Thumb bit cleared, which means the subsequent comparison is guaranteed to fail. Instead, use the badr macro, which forces the Thumb bit to be set.Fixes a3ba87a61499 ("ARM: 6316/1: ftrace: add Thumb-2 support")Signed-off-by Ard Biesheuvel <[email protected]>
Quoted 20 lines
--- arch/arm/kernel/entry-ftrace.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)arch/arm/kernel/entry-ftrace.S +1
-2@@ -40,7 +40,7 @@ mcount_enter ldr r0, =ftrace_trace_function ldr r2, [r0] - adr r0, .Lftrace_stub + badr r0, .Lftrace_stub cmp r0, r2 bne 1f --2.30.2
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Thanks, ~Nick Desaulniers _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Re: [PATCH 1/8] ARM: ftrace: ensure that ADR take Thumb bit into account
In reply to Ard BiesheuvelQuoted 7 lines · Ard Biesheuvel
Using ADR to take the address of '
ftrace_stub' via a local label produces an address that has the Thumb bit cleared, which means the subsequent comparison is guaranteed to fail. Instead, use the badr macro, which forces the Thumb bit to be set.Fixes a3ba87a61499 ("ARM: 6316/1: ftrace: add Thumb-2 support")Signed-off-by Ard Biesheuvel <[email protected]>
Looks correct to me!
Yours,
Linus Walleij
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PATCH 2/8 ARM: ftrace: use ADD not POP to counter PUSH at entry
In reply to Ard BiesheuvelThe compiler emitted hook used for ftrace consists of a PUSH {LR} to preserve the link register, followed by a branch-and-link (BL) to __gnu_mount_nc. Dynamic ftrace patches away the latter to turn the combined sequence into a NOP, using a POP {LR} instruction.
This is not necessary, since the link register does not get clobbered in this case, and simply adding #4 to the stack pointer is sufficient, and avoids a memory access that may take a few cycles to resolve depending on the micro-architecture.
--- arch/arm/kernel/entry-ftrace.S | 2 +- arch/arm/kernel/ftrace.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-)
arch/arm/kernel/entry-ftrace.S +1 -1
@@ -27,7 +27,7 @@ * allows it to be clobbered in subroutines and doesn't use it to hold * parameters.) * - * When using dynamic ftrace, we patch out the mcount call by a "pop {lr}" + * When using dynamic ftrace, we patch out the mcount call by a "add sp, #4" * instead of the __gnu_mcount_nc call (see arch/arm/kernel/ftrace.c). */
arch/arm/kernel/ftrace.c +2 -2
@@ -25,9 +25,9 @@#include <asm/patch.h> #ifdef CONFIG_THUMB2_KERNEL -#define NOP 0xf85deb04/* pop.w {lr} */ +#define NOP 0xf10d0d04/* add.w sp, sp, #4 */ #else -#define NOP 0xe8bd4000/* pop {lr} */ +#define NOP 0xe28dd004/* add sp, sp, #4 */ #endif #ifdef CONFIG_DYNAMIC_FTRACE
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2.30.2 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Re: [PATCH 2/8] ARM: ftrace: use ADD not POP to counter PUSH at entry
Quoted 10 lines · Ard Biesheuvel
The compiler emitted hook used for ftrace consists of a PUSH {LR} to preserve the link register, followed by a branch-and-link (BL) to
__gnu_mount_nc. Dynamic ftrace patches away the latter to turn the combined sequence into a NOP, using a POP {LR} instruction.This is not necessary, since the link register does not get clobbered in this case, and simply adding #4 to the stack pointer is sufficient, and avoids a memory access that may take a few cycles to resolve depending on the micro-architecture.
Quoted 39 lines
Signed-off-by Ard Biesheuvel <[email protected]>--- arch/arm/kernel/entry-ftrace.S | 2 +- arch/arm/kernel/ftrace.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-)arch/arm/kernel/entry-ftrace.S +1
-1@@ -27,7 +27,7 @@ * allows it to be clobbered in subroutines and doesn't use it to hold * parameters.) * - * When using dynamic ftrace, we patch out the mcount call by a "pop {lr}" + * When using dynamic ftrace, we patch out the mcount call by a "add sp, #4" * instead of the __gnu_mcount_nc call (see arch/arm/kernel/ftrace.c). */arch/arm/kernel/ftrace.c +2
-3@@ -25,9 +25,9 @@#include <asm/patch.h> #ifdef CONFIG_THUMB2_KERNEL -#define NOP 0xf85deb04/* pop.w {lr} */ +#define NOP 0xf10d0d04/* add.w sp, sp, #4 */ #else -#define NOP 0xe8bd4000/* pop {lr} */ +#define NOP 0xe28dd004/* add sp, sp, #4 */ #endif #ifdef CONFIG_DYNAMIC_FTRACE --2.30.2
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Thanks, ~Nick Desaulniers _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Re: [PATCH 2/8] ARM: ftrace: use ADD not POP to counter PUSH at entry
In reply to Ard BiesheuvelQuoted 11 lines · Ard Biesheuvel
The compiler emitted hook used for ftrace consists of a PUSH {LR} to preserve the link register, followed by a branch-and-link (BL) to
__gnu_mount_nc. Dynamic ftrace patches away the latter to turn the combined sequence into a NOP, using a POP {LR} instruction.This is not necessary, since the link register does not get clobbered in this case, and simply adding #4 to the stack pointer is sufficient, and avoids a memory access that may take a few cycles to resolve depending on the micro-architecture.
Signed-off-by Ard Biesheuvel <[email protected]>
That's on the hotpath for ftrace so definitely worth optimizing!
Maybe some of the commit message should go into
the code comment as well? "The compiler hook pushed 4 bytes with a PUSH{LR}, so discard them by simply adding 4 to the stack pointer" or so? Just a suggestion.
Yours,
Linus Walleij
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PATCH 3/8 ARM: ftrace: use trampolines to keep .init.text in branching range
In reply to Ard BiesheuvelKernel images that are large in comparison to the range of a direct branch may fail to work as expected with ftrace, as patching a direct branch to one of the core ftrace routines may not be possible from the .init.text section, if it is emitted too far away from the normal .text section.
This is more likely to affect Thumb2 builds, given that its range is only -/+ 16 MiB (as opposed to ARM which has -/+ 32 MiB), but may occur in either ISA.
To work around this, add a couple of trampolines to .init.text and swap these in when the ftrace patching code is operating on callers in .init.text.
--- arch/arm/kernel/entry-ftrace.S | 16 ++++++++++++++++ arch/arm/kernel/ftrace.c | 19 +++++++++++++++++-- 2 files changed, 33 insertions(+), 2 deletions(-)
arch/arm/kernel/entry-ftrace.S +16 -0
@@ -270,3 +270,19 @@ ENTRY(ftrace_stub) .Lftrace_stub: ret lr ENDPROC(ftrace_stub) + +#ifdef CONFIG_DYNAMIC_FTRACE + + __INIT + + .macro init_tramp, dst:req +ENTRY(\dst\()_from_init) + ldr pc, =\dst +ENDPROC(\dst\()_from_init) + .endm + + init_tramp ftrace_caller +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS + init_tramp ftrace_regs_caller +#endif +#endif
arch/arm/kernel/ftrace.c +17 -2
@@ -51,9 +51,18 @@ static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)return NOP ; } +void ftrace_caller_from_init (void ); +void ftrace_regs_caller_from_init (void ); +static unsigned long adjust_address (struct dyn_ftrace *rec,unsigned long addr) { -return addr; +if (!IS_ENABLED (CONFIG_DYNAMIC_FTRACE ) || +likely (!is_kernel_inittext (rec->ip))) +return addr; +if (!IS_ENABLED (CONFIG_DYNAMIC_FTRACE_WITH_REGS ) || + addr == (unsigned long )&ftrace_caller) +return (unsigned long )&ftrace_caller_from_init; +return (unsigned long )&ftrace_regs_caller_from_init; }int ftrace_arch_code_modify_prepare (void )
@@ -189,7 +198,13 @@ int ftrace_make_nop(struct module *mod,#endif new =ftrace_nop_replace (rec); - ret =ftrace_modify_code (ip, old, new, true); +/* +* Locations in .init.text may call __gnu_mcount_mc via a linker +* emitted veneer if they are too far away from its implementation, and +* so validation may fail spuriously in such cases. Let's work around +* this by omitting those from validation. +*/ + ret =ftrace_modify_code (ip, old, new, !is_kernel_inittext (ip));return ret; }
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2.30.2 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Re: [PATCH 3/8] ARM: ftrace: use trampolines to keep .init.text in branching range
Quoted 34 lines · Ard Biesheuvel
Kernel images that are large in comparison to the range of a direct branch may fail to work as expected with ftrace, as patching a direct branch to one of the core ftrace routines may not be possible from the .init.text section, if it is emitted too far away from the normal .text section.
This is more likely to affect Thumb2 builds, given that its range is only -/+ 16 MiB (as opposed to ARM which has -/+ 32 MiB), but may occur in either ISA.
To work around this, add a couple of trampolines to .init.text and swap these in when the ftrace patching code is operating on callers in .init.text.
Signed-off-by Ard Biesheuvel <[email protected]>--- arch/arm/kernel/entry-ftrace.S | 16 ++++++++++++++++ arch/arm/kernel/ftrace.c | 19 +++++++++++++++++-- 2 files changed, 33 insertions(+), 2 deletions(-)arch/arm/kernel/entry-ftrace.S +5
-0@@ -270,3 +270,19 @@ ENTRY(ftrace_stub) .Lftrace_stub: ret lr ENDPROC(ftrace_stub) + +#ifdef CONFIG_DYNAMIC_FTRACE + + __INIT +
arch/arm/kernel/entry-ftrace.S ENTRY(ftrace_stub) · line 287
Quoted 10 lines
arch/arm/kernel/entry-ftrace.S +10
-0+ .macro init_tramp, dst:req +ENTRY(\dst\()_from_init) + ldr pc, =\dst +ENDPROC(\dst\()_from_init) + .endm + + init_tramp ftrace_caller +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS + init_tramp ftrace_regs_caller +#endif
Consider adding __FINIT here; while it's not necessary now, folks who append new code to this file might be surprised to find new code in .init.text. I would also tighten up the __INIT/__FINIT to only surround the invocations of init_tramp and not the macro definition itself.
Either way,
Quoted 43 lines
arch/arm/kernel/entry-ftrace.S +1
-0+#endifarch/arm/kernel/ftrace.c +17
-3@@ -51,9 +51,18 @@ static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)return NOP ; } +void ftrace_caller_from_init (void ); +void ftrace_regs_caller_from_init (void ); +static unsigned long adjust_address (struct dyn_ftrace *rec,unsigned long addr) { -return addr; +if (!IS_ENABLED (CONFIG_DYNAMIC_FTRACE ) || +likely (!is_kernel_inittext (rec->ip))) +return addr; +if (!IS_ENABLED (CONFIG_DYNAMIC_FTRACE_WITH_REGS ) || + addr == (unsigned long )&ftrace_caller) +return (unsigned long )&ftrace_caller_from_init; +return (unsigned long )&ftrace_regs_caller_from_init; }int ftrace_arch_code_modify_prepare (void )@@ -189,7 +198,13 @@ int ftrace_make_nop(struct module *mod,#endif new =ftrace_nop_replace (rec); - ret =ftrace_modify_code (ip, old, new, true); +/* +* Locations in .init.text may call __gnu_mcount_mc via a linker +* emitted veneer if they are too far away from its implementation, and +* so validation may fail spuriously in such cases. Let's work around +* this by omitting those from validation. +*/ + ret =ftrace_modify_code (ip, old, new, !is_kernel_inittext (ip));return ret; } --2.30.2
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Thanks, ~Nick Desaulniers _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Re: [PATCH 3/8] ARM: ftrace: use trampolines to keep .init.text in branching range
In reply to Ard BiesheuvelQuoted 10 lines · Ard Biesheuvel
Kernel images that are large in comparison to the range of a direct branch may fail to work as expected with ftrace, as patching a direct branch to one of the core ftrace routines may not be possible from the .init.text section, if it is emitted too far away from the normal .text section.
This is more likely to affect Thumb2 builds, given that its range is only -/+ 16 MiB (as opposed to ARM which has -/+ 32 MiB), but may occur in either ISA.
Quoted 5 lines
To work around this, add a couple of trampolines to .init.text and swap these in when the ftrace patching code is operating on callers in .init.text.
Signed-off-by Ard Biesheuvel <[email protected]>
LGTM
I suppose part of me wonder what happens if .text itself grows larger than 16MB under thumb2, but I guess then the linker will just fail.
Yours,
Linus Walleij
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PATCH 4/8 ARM: ftrace: avoid redundant loads or clobbering IP
In reply to Ard BiesheuvelTweak the ftrace return paths to avoid redundant loads of SP, as well as unnecessary clobbering of IP.
This also fixes the inconsistency of using MOV to perform a function return, which is sub-optimal on recent micro-architectures but more importantly, does not perform an interworking return, unlike compiler generated function returns in Thumb2 builds.
Let's fix this by popping PC from the stack like most ordinary code does.
--- arch/arm/kernel/entry-ftrace.S | 51 +++++++++----------- 1 file changed, 22 insertions(+), 29 deletions(-)
arch/arm/kernel/entry-ftrace.S +22 -29
@@ -22,10 +22,7 @@ * mcount can be thought of as a function called in the middle of a subroutine * call. As such, it needs to be transparent for both the caller and the * callee: the original lr needs to be restored when leaving mcount, and no - * registers should be clobbered. (In the __gnu_mcount_nc implementation, we - * clobber the ip register. This is OK because the ARM calling convention - * allows it to be clobbered in subroutines and doesn't use it to hold - * parameters.) + * registers should be clobbered. * * When using dynamic ftrace, we patch out the mcount call by a "add sp, #4" * instead of the __gnu_mcount_nc call (see arch/arm/kernel/ftrace.c).
@@ -70,26 +67,25 @@ .macro __ftrace_regs_caller - sub sp, sp, #8 @ space for PC and CPSR OLD_R0, + str lr, [sp, #-8]! @ store LR as PC and make space for CPSR/OLD_R0, @ OLD_R0 will overwrite previous LR - add ip, sp, #12 @ move in IP the value of SP as it was - @ before the push {lr} of the mcount mechanism + ldr lr, [sp, #8] @ get previous LR - str lr, [sp, #0] @ store LR instead of PC + str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR - ldr lr, [sp, #8] @ get previous LR + str lr, [sp, #-4]! @ store previous LR as LR - str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR + add lr, sp, #16 @ move in LR the value of SP as it was + @ before the push {lr} of the mcount mechanism - stmdb sp!, {ip, lr} - stmdb sp!, {r0-r11, lr} + push {r0-r11, ip, lr} @ stack content at this point: @ 0 4 48 52 56 60 64 68 72 - @ R0 | R1 | ... | LR | SP + 4 | previous LR | LR | PSR | OLD_R0 | + @ R0 | R1 | ... | IP | SP + 4 | previous LR | LR | PSR | OLD_R0 | - mov r3, sp @ struct pt_regs* + mov r3, sp @ struct pt_regs* ldr r2, =function_trace_op ldr r2, [r2] @ pointer to the current
@@ -112,11 +108,9 @@ ftrace_graph_regs_call: #endif @ pop saved regs - ldmia sp!, {r0-r12} @ restore r0 through r12 - ldr ip, [sp, #8] @ restore PC - ldr lr, [sp, #4] @ restore LR - ldr sp, [sp, #0] @ restore SP - mov pc, ip @ return + pop {r0-r11, ip, lr} @ restore r0 through r12 + ldr lr, [sp], #4 @ restore LR + ldr pc, [sp], #12 .endm #ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -132,11 +126,9 @@ ftrace_graph_regs_call: bl prepare_ftrace_return @ pop registers saved in ftrace_regs_caller - ldmia sp!, {r0-r12} @ restore r0 through r12 - ldr ip, [sp, #8] @ restore PC - ldr lr, [sp, #4] @ restore LR - ldr sp, [sp, #0] @ restore SP - mov pc, ip @ return + pop {r0-r11, ip, lr} @ restore r0 through r12 + ldr lr, [sp], #4 @ restore LR + ldr pc, [sp], #12 .endm #endif
@@ -202,16 +194,17 @@ ftrace_graph_call\suffix: .endm .macro mcount_exit - ldmia sp!, {r0-r3, ip, lr} - ret ip + ldmia sp!, {r0-r3} + ldr lr, [sp, #4] + ldr pc, [sp], #8 .endm ENTRY(__gnu_mcount_nc) UNWIND(.fnstart) #ifdef CONFIG_DYNAMIC_FTRACE - mov ip, lr - ldmia sp!, {lr} - ret ip + push {lr} + ldr lr, [sp, #4] + ldr pc, [sp], #8 #else __mcount #endif
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2.30.2 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
PATCH 5/8 ARM: ftrace: avoid unnecessary literal loads
In reply to Ard BiesheuvelAvoid explicit literal loads and instead, use accessor macros that generate the optimal sequence depending on the architecture revision being targeted.
--- arch/arm/kernel/entry-ftrace.S | 27 ++++++++------------ 1 file changed, 11 insertions(+), 16 deletions(-)
arch/arm/kernel/entry-ftrace.S +11 -16
@@ -35,23 +35,20 @@ .macro __mcount suffix mcount_enter - ldr r0, =ftrace_trace_function - ldr r2, [r0] + ldr_va r2, ftrace_trace_function badr r0, .Lftrace_stub cmp r0, r2 bne 1f #ifdef CONFIG_FUNCTION_GRAPH_TRACER - ldr r1, =ftrace_graph_return - ldr r2, [r1] - cmp r0, r2 - bne ftrace_graph_caller\suffix - - ldr r1, =ftrace_graph_entry - ldr r2, [r1] - ldr r0, =ftrace_graph_entry_stub - cmp r0, r2 - bne ftrace_graph_caller\suffix + ldr_va r2, ftrace_graph_return + cmp r0, r2 + bne ftrace_graph_caller\suffix + + ldr_va r2, ftrace_graph_entry + mov_l r0, ftrace_graph_entry_stub + cmp r0, r2 + bne ftrace_graph_caller\suffix #endif mcount_exit
@@ -87,8 +84,7 @@ mov r3, sp @ struct pt_regs* - ldr r2, =function_trace_op - ldr r2, [r2] @ pointer to the current + ldr_va r2, function_trace_op @ pointer to the current @ function tracing op ldr r1, [sp, #S_LR] @ lr of instrumented func
@@ -141,8 +137,7 @@ ftrace_graph_regs_call: mcount_adjust_addr r0, lr @ instrumented function #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS - ldr r2, =function_trace_op - ldr r2, [r2] @ pointer to the current + ldr_va r2, function_trace_op @ pointer to the current @ function tracing op mov r3, #0 @ regs is NULL #endif
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2.30.2 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Re: [PATCH 5/8] ARM: ftrace: avoid unnecessary literal loads
Quoted 6 lines · Ard Biesheuvel
Avoid explicit literal loads and instead, use accessor macros that generate the optimal sequence depending on the architecture revision being targeted.
Signed-off-by Ard Biesheuvel <[email protected]>
Note to fellow reviewers, Ard pointed out to me that the definition of ldr_va depends on his vmapped stack series:
https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?h=arm-up-ti-in-task-v4&id=4e918ab13eaf40f19938659cb5a22c93172778a8
("ARM: assembler: add optimized ldr/str macros to load variables from memory")
Quoted 64 lines
--- arch/arm/kernel/entry-ftrace.S | 27 ++++++++------------ 1 file changed, 11 insertions(+), 16 deletions(-)arch/arm/kernel/entry-ftrace.S +11
-17@@ -35,23 +35,20 @@ .macro __mcount suffix mcount_enter - ldr r0, =ftrace_trace_function - ldr r2, [r0] + ldr_va r2, ftrace_trace_function badr r0, .Lftrace_stub cmp r0, r2 bne 1f #ifdef CONFIG_FUNCTION_GRAPH_TRACER - ldr r1, =ftrace_graph_return - ldr r2, [r1] - cmp r0, r2 - bne ftrace_graph_caller\suffix - - ldr r1, =ftrace_graph_entry - ldr r2, [r1] - ldr r0, =ftrace_graph_entry_stub - cmp r0, r2 - bne ftrace_graph_caller\suffix + ldr_va r2, ftrace_graph_return + cmp r0, r2 + bne ftrace_graph_caller\suffix + + ldr_va r2, ftrace_graph_entry + mov_l r0, ftrace_graph_entry_stub + cmp r0, r2 + bne ftrace_graph_caller\suffix #endif mcount_exit@@ -87,8 +84,7 @@ mov r3, sp @ struct pt_regs* - ldr r2, =function_trace_op - ldr r2, [r2] @ pointer to the current + ldr_va r2, function_trace_op @ pointer to the current @ function tracing op ldr r1, [sp, #S_LR] @ lr of instrumented func@@ -141,8 +137,7 @@ ftrace_graph_regs_call: mcount_adjust_addr r0, lr @ instrumented function #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS - ldr r2, =function_trace_op - ldr r2, [r2] @ pointer to the current + ldr_va r2, function_trace_op @ pointer to the current @ function tracing op mov r3, #0 @ regs is NULL #endif --2.30.2
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Thanks, ~Nick Desaulniers _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
PATCH 6/8 ARM: ftrace: enable HAVE_FUNCTION_GRAPH_FP_TEST
In reply to Ard BiesheuvelFix the frame pointer handling in the function graph tracer entry and exit code so we can enable HAVE_FUNCTION_GRAPH_FP_TEST. Instead of using FP directly (which will have different values between the entry and exit pieces of the function graph tracer), use the value of SP at entry and exit, as we can derive the former value from the frame pointer.
--- arch/arm/include/asm/ftrace.h | 2 ++ arch/arm/kernel/entry-ftrace.S | 2 +- arch/arm/kernel/ftrace.c | 5 +++++ 3 files changed, 8 insertions(+), 1 deletion(-)
arch/arm/include/asm/ftrace.h +2 -0
@@ -2,6 +2,8 @@#ifndef _ASM_ARM_FTRACE#define _ASM_ARM_FTRACE +#define HAVE_FUNCTION_GRAPH_FP_TEST +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS #define ARCH_SUPPORTS_FTRACE_OPS 1#endif
arch/arm/kernel/entry-ftrace.S +1 -1
@@ -247,7 +247,7 @@ ENDPROC(ftrace_graph_regs_caller) .globl return_to_handler return_to_handler: stmdb sp!, {r0-r3} - mov r0, fp @ frame pointer + add r0, sp, #16 @ sp at exit of instrumented routine bl ftrace_return_to_handler mov lr, r0 @ r0 has real ret addr ldmia sp!, {r0-r3}
arch/arm/kernel/ftrace.c +5 -0
@@ -220,6 +220,11 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,if (unlikely (atomic_read (¤t->tracing_graph_pause)))return ; +if (IS_ENABLED (CONFIG_UNWINDER_FRAME_POINTER )) { +/* FP points one word below parent's top of stack */ + frame_pointer +=4 ; + } + old = *parent; *parent = return_hooker;
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2.30.2 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
PATCH 7/8 ARM: unwind: track location of LR value in stack frame
In reply to Ard BiesheuvelThe ftrace graph tracer needs to override the return address of an instrumented function, in order to install a hook that gets invoked when the function returns again.
Currently, we only support this when building for ARM using GCC with frame pointers, as in this case, it is guaranteed that the function will reload LR from [FP, #-4] in all cases, and we can simply pass that address to the ftrace code.
In order to support this for configurations that rely on the EABI unwinder, such as Thumb2 builds, make the unwinder keep track of the address from which LR was unwound, permitting ftrace to make use of this in a subsequent patch.
Drop the call to is_kernel_text_address(), which is problematic in terms of ftrace recursion, given that it may be instrumented itself. The call is redundant anyway, as no unwind directives will be found unless the PC points to memory that is known to contain executable code.
--- arch/arm/include/asm/stacktrace.h | 2 ++ arch/arm/kernel/Makefile | 1 + arch/arm/kernel/unwind.c | 7 ++++--- 3 files changed, 7 insertions(+), 3 deletions(-)
arch/arm/include/asm/stacktrace.h +2 -0
@@ -27,6 +27,8 @@ struct stackframe {* executing from another stack. */ unsigned long sp_low; +/* address of the LR value on the stack */ +unsigned long *lr_addr;#endif };
arch/arm/kernel/Makefile +1 -0
@@ -10,6 +10,7 @@ ifdef CONFIG_FUNCTION_TRACER CFLAGS_REMOVE_ftrace.o = -pg CFLAGS_REMOVE_insn.o = -pg CFLAGS_REMOVE_patch.o = -pg +CFLAGS_REMOVE_unwind.o = -pg endif CFLAGS_REMOVE_return_address.o = -pg
arch/arm/kernel/unwind.c +4 -3
@@ -55,6 +55,7 @@ struct unwind_ctrl_block {const unsigned long *insn;/* pointer to the current instructions word */ unsigned long sp_low;/* lowest value of sp allowed */ unsigned long sp_high;/* highest value of sp allowed */ +unsigned long *lr_addr;/* address of LR value on the stack */ /* * 1 : check for stack overflow for each register pop. * 0 : save overhead if there is plenty of stack remaining.
@@ -239,6 +240,8 @@ static int unwind_pop_register(struct unwind_ctrl_block *ctrl,* from being tracked by KASAN. */ ctrl->vrs[reg] =READ_ONCE_NOCHECK (*(*vsp)); +if (reg ==14 ) + ctrl->lr_addr = *vsp; (*vsp)++;return URC_OK ; }
@@ -395,9 +398,6 @@ int unwind_frame(struct stackframe *frame)pr_debug ("%s(pc = %08lx lr = %08lx sp = %08lx)\n" , __func__, frame->pc, frame->lr, frame->sp); -if (!kernel_text_address (frame->pc)) -return -URC_FAILURE ; - idx =unwind_find_idx (frame->pc);if (!idx) {pr_warn ("unwind: Index not found %08lx\n" , frame->pc);
@@ -476,6 +476,7 @@ int unwind_frame(struct stackframe *frame) frame->lr = ctrl.vrs[LR ]; frame->pc = ctrl.vrs[PC ]; frame->sp_low = ctrl.sp_low; + frame->lr_addr = ctrl.lr_addr;return URC_OK ; }
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2.30.2 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
PATCH 8/8 ARM: ftrace: enable the graph tracer with the EABI unwinder
In reply to Ard BiesheuvelEnable the function graph tracer in combination with the EABI unwinder, so that Thumb2 builds or Clang ARM builds can make use of it.
This involves using the unwinder to locate the return address of an instrumented function on the stack, so that it can be overridden and made to refer to the ftrace handling routines that need to be called at function return.
Given that for these builds, it is not guaranteed that the value of the link register is stored on the stack, fall back to the stack slot that will be used by the ftrace exit code to restore LR in the instrumented function's execution context.
--- arch/arm/Kconfig | 2 +- arch/arm/Kconfig.debug | 2 +- arch/arm/include/asm/ftrace.h | 18 ------------- arch/arm/kernel/Makefile | 5 +--- arch/arm/kernel/entry-ftrace.S | 28 ++++++++++++++------ arch/arm/kernel/ftrace.c | 19 +++++++++++-- 6 files changed, 40 insertions(+), 34 deletions(-)
arch/arm/Kconfig +1 -1
@@ -92,7 +92,7 @@ config ARM select HAVE_EXIT_THREAD select HAVE_FAST_GUP if ARM_LPAE select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL - select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG + select HAVE_FUNCTION_GRAPH_TRACER select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !(THUMB2_KERNEL && CC_IS_CLANG) select HAVE_GCC_PLUGINS select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
arch/arm/Kconfig.debug +1 -1
@@ -65,7 +65,7 @@ config UNWINDER_FRAME_POINTER config UNWINDER_ARM bool "ARM EABI stack unwinder" - depends on AEABI && !FUNCTION_GRAPH_TRACER + depends on AEABI select ARM_UNWIND help This option enables stack unwinding support in the kernel
arch/arm/include/asm/ftrace.h +0 -18
@@ -35,26 +35,8 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)#ifndef __ASSEMBLY__ -#if defined(CONFIG_FRAME_POINTER ) && !defined(CONFIG_ARM_UNWIND ) -/* -* return_address uses walk_stackframe to do it's work. If both -* CONFIG_FRAME_POINTER=y and CONFIG_ARM_UNWIND=y walk_stackframe uses unwind -* information. For this to work in the function tracer many functions would -* have to be marked with __notrace. So for now just depend on -* !CONFIG_ARM_UNWIND. -*/ -void *return_address (unsigned int ); -#else - -static inline void *return_address (unsigned int level) -{ -return NULL ; -} - -#endif -#define ftrace_return_address (n) return_address(n)#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
arch/arm/kernel/Makefile +1 -4
@@ -25,10 +25,7 @@ obj-y := elf.o entry-common.o irq.o opcodes.o \ KASAN_SANITIZE_stacktrace.o := n KASAN_SANITIZE_traps.o := n -ifneq ($(CONFIG_ARM_UNWIND),y) -obj-$(CONFIG_FRAME_POINTER) += return_address.o -endif - +obj-y += return_address.o obj-$(CONFIG_ATAGS) += atags_parse.o obj-$(CONFIG_ATAGS_PROC) += atags_proc.o obj-$(CONFIG_DEPRECATED_PARAM_STRUCT) += atags_compat.o
arch/arm/kernel/entry-ftrace.S +20 -8
@@ -100,7 +100,8 @@ ftrace_regs_call: #ifdef CONFIG_FUNCTION_GRAPH_TRACER .globl ftrace_graph_regs_call ftrace_graph_regs_call: - mov r0, r0 +ARM( mov r0, r0 ) +THUMB( nop.w ) #endif @ pop saved regs
@@ -112,13 +113,18 @@ ftrace_graph_regs_call: #ifdef CONFIG_FUNCTION_GRAPH_TRACER .macro __ftrace_graph_regs_caller - sub r0, fp, #4 @ lr of instrumented routine (parent) +#ifdef CONFIG_UNWINDER_FRAME_POINTER + sub r0, fp, #4 @ lr of instrumented routine (parent) +#else + add r0, sp, #S_LR +#endif @ called from __ftrace_regs_caller - ldr r1, [sp, #S_PC] @ instrumented routine (func) + ldr r1, [sp, #S_PC] @ instrumented routine (func) mcount_adjust_addr r1, r1 - mov r2, fp @ frame pointer + mov r2, fpreg @ frame pointer + add r3, sp, #PT_REGS_SIZE bl prepare_ftrace_return @ pop registers saved in ftrace_regs_caller
@@ -149,14 +155,19 @@ ftrace_call\suffix: #ifdef CONFIG_FUNCTION_GRAPH_TRACER .globl ftrace_graph_call\suffix ftrace_graph_call\suffix: - mov r0, r0 +ARM( mov r0, r0 ) +THUMB( nop.w ) #endif mcount_exit .endm .macro __ftrace_graph_caller +#ifdef CONFIG_UNWINDER_FRAME_POINTER sub r0, fp, #4 @ &lr of instrumented routine (&parent) +#else + add r0, sp, #20 +#endif #ifdef CONFIG_DYNAMIC_FTRACE @ called from __ftrace_caller, saved in mcount_enter ldr r1, [sp, #16] @ instrumented routine (func)
@@ -165,7 +176,8 @@ ftrace_graph_call\suffix: @ called from __mcount, untouched in lr mcount_adjust_addr r1, lr @ instrumented routine (func) #endif - mov r2, fp @ frame pointer + mov r2, fpreg @ frame pointer + add r3, sp, #24 bl prepare_ftrace_return mcount_exit .endm
@@ -244,14 +256,14 @@ ENDPROC(ftrace_graph_regs_caller) .purgem mcount_exit #ifdef CONFIG_FUNCTION_GRAPH_TRACER - .globl return_to_handler -return_to_handler: +ENTRY(return_to_handler) stmdb sp!, {r0-r3} add r0, sp, #16 @ sp at exit of instrumented routine bl ftrace_return_to_handler mov lr, r0 @ r0 has real ret addr ldmia sp!, {r0-r3} ret lr +ENDPROC(return_to_handler) #endif ENTRY(ftrace_stub)
arch/arm/kernel/ftrace.c +17 -2
@@ -22,6 +22,7 @@#include <asm/ftrace.h> #include <asm/insn.h> #include <asm/set_memory.h> +#include <asm/stacktrace.h> #include <asm/patch.h> #ifdef CONFIG_THUMB2_KERNEL
@@ -211,8 +212,10 @@ int ftrace_make_nop(struct module *mod,#endif /* CONFIG_DYNAMIC_FTRACE */ #ifdef CONFIG_FUNCTION_GRAPH_TRACER +asmlinkage void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, -unsigned long frame_pointer) +unsigned long frame_pointer, +unsigned long stack_pointer) {unsigned long return_hooker = (unsigned long ) &return_to_handler;unsigned long old;
@@ -223,6 +226,18 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,if (IS_ENABLED (CONFIG_UNWINDER_FRAME_POINTER )) {/* FP points one word below parent's top of stack */ frame_pointer +=4 ; + }else { +struct stackframe frame = { + .fp = frame_pointer, + .sp = stack_pointer, + .lr = self_addr, + .pc = self_addr, + }; +if (unwind_frame (&frame) <0 ) +return ; +if (frame.lr != self_addr) + parent = frame.lr_addr; + frame_pointer = frame.sp; } old = *parent;
@@ -245,7 +260,7 @@ static int __ftrace_modify_caller(unsigned long *callsite,unsigned long caller_fn = (unsigned long ) func;unsigned long pc = (unsigned long ) callsite;unsigned long branch =arm_gen_branch (pc, caller_fn); -unsigned long nop =0xe1a00000 ;/* mov r0, r0 */ +unsigned long nop =arm_gen_nop ();unsigned long old = enable ? nop : branch;unsigned long new = enable ? branch : nop;
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2.30.2 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel