| Message ID | 1394705630-12384-6-git-send-email-takahiro.akashi@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Mar 13, 2014 at 10:13:48AM +0000, AKASHI Takahiro wrote: > This patch allows "dynamic ftrace" if CONFIG_DYNAMIC_FTRACE is enabled. > Here we can turn on and off tracing dynamically per-function base. > > On arm64, this is done by patching single branch instruction to _mcount() > inserted by gcc -pg option. The branch is replaced to NOP initially at > kernel start up, and later on, NOP to branch to ftrace_caller() when > enabled or branch to NOP when disabled. > Please note that ftrace_caller() is a counterpart of _mcount() in case of > 'static' ftrace. > > More details on architecture specific requirements are described in > Documentation/trace/ftrace-design.txt. > > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/ftrace.h | 15 +++++ > arch/arm64/kernel/entry-ftrace.S | 43 +++++++++++++++ > arch/arm64/kernel/ftrace.c | 113 ++++++++++++++++++++++++++++++++++++++ > 4 files changed, 172 insertions(+) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 6b3fef6..6954959 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -33,6 +33,7 @@ config ARM64 > select HAVE_DMA_API_DEBUG > select HAVE_DMA_ATTRS > select HAVE_DMA_CONTIGUOUS > + select HAVE_DYNAMIC_FTRACE > select HAVE_EFFICIENT_UNALIGNED_ACCESS > select HAVE_FTRACE_MCOUNT_RECORD > select HAVE_FUNCTION_TRACER > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > index 58ea595..ed5c448 100644 > --- a/arch/arm64/include/asm/ftrace.h > +++ b/arch/arm64/include/asm/ftrace.h > @@ -18,6 +18,21 @@ > > #ifndef __ASSEMBLY__ > extern void _mcount(unsigned long); > + > +struct dyn_arch_ftrace { > + /* No extra data needed for arm64 */ > +}; > + > +extern unsigned long ftrace_graph_call; > + > +static inline unsigned long ftrace_call_adjust(unsigned long addr) > +{ > + /* > + * addr is the address of the mcount call instruction. > + * recordmcount does the necessary offset calculation. > + */ > + return addr; > +} You could just as easily implement this as a dummy macro, but I guess it doesn't matter either way. > #endif /* __ASSEMBLY__ */ > > #endif /* __ASM_FTRACE_H */ > diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S > index 0ac31c8..c0fbe10 100644 > --- a/arch/arm64/kernel/entry-ftrace.S > +++ b/arch/arm64/kernel/entry-ftrace.S > @@ -86,6 +86,7 @@ > add \reg, \reg, #8 > .endm > > +#ifndef CONFIG_DYNAMIC_FTRACE > /* > * void _mcount(unsigned long return_address) > * @return_address: return address to instrumented function > @@ -134,6 +135,48 @@ skip_ftrace_call: > #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ > ENDPROC(_mcount) > > +#else /* CONFIG_DYNAMIC_FTRACE */ > +/* > + * _mcount() is used to build the kernel with -pg option, but all the branch > + * instructions to _mcount() are replaced to NOP initially at kernel start up, > + * and later on, NOP to branch to ftrace_caller() when enabled or branch to > + * NOP when disabled per-function base. > + */ > +ENTRY(_mcount) > + ret > +ENDPROC(_mcount) Judging by your comment then, this should never be called. Is that right? If so, we could add a BUG-equivalent so we know if we missed an mcount during patching. > +/* > + * void ftrace_caller(unsigned long return_address) > + * @return_address: return address to instrumented function > + * > + * This function is a counterpart of _mcount() in 'static' ftrace, and > + * makes calls to: > + * - tracer function to probe instrumented function's entry, > + * - ftrace_graph_caller to set up an exit hook > + */ > +ENTRY(ftrace_caller) > + mcount_enter > + > + mcount_get_pc0 x0 // function's pc > + mcount_get_lr x1 // function's lr > + > + .global ftrace_call > +ftrace_call: // tracer(pc, lr); > + nop // This will be replaced with "bl xxx" > + // where xxx can be any kind of tracer. > + > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER > + .global ftrace_graph_call > +ftrace_graph_call: // ftrace_graph_caller(); > + nop // If enabled, this will be replaced > + // "b ftrace_graph_caller" > +#endif > + > + mcount_exit > +ENDPROC(ftrace_caller) > +#endif /* CONFIG_DYNAMIC_FTRACE */ > + > ENTRY(ftrace_stub) > ret > ENDPROC(ftrace_stub) > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > index a559ab8..8c26476 100644 > --- a/arch/arm64/kernel/ftrace.c > +++ b/arch/arm64/kernel/ftrace.c > @@ -17,6 +17,89 @@ > #include <asm/ftrace.h> > #include <asm/insn.h> > > +#ifdef CONFIG_DYNAMIC_FTRACE > +/* > + * Replace a single instruction, which may be a branch or NOP. > + * If @validate == true, a replaced instruction is checked against 'old'. > + */ > +static int ftrace_modify_code(unsigned long pc, unsigned int old, > + unsigned int new, bool validate) > +{ > + unsigned int replaced; u32 is a bit clearer for instructions. > + /* > + * Note: > + * Due to modules and __init, code can disappear and change, > + * we need to protect against faulting as well as code changing. > + * We do this by aarch64_insn_*() which use the probe_kernel_*(). > + * > + * No lock is held here because all the modifications are run > + * through stop_machine(). > + */ > + if (validate) { > + if (aarch64_insn_read((void *)pc, &replaced)) > + return -EFAULT; > + > + if (replaced != old) > + return -EINVAL; > + } > + if (aarch64_insn_patch_text_nosync((void *)pc, new)) > + return -EPERM; I think you're better off propagating the errors here, rather than overriding them with EFAULT/EINVAL/EPERM. > + > + return 0; > +} > + > +/* > + * Replace tracer function in ftrace_caller() > + */ > +int ftrace_update_ftrace_func(ftrace_func_t func) > +{ > + unsigned long pc; > + unsigned int new; > + > + pc = (unsigned long)&ftrace_call; > + new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, true); > + > + return ftrace_modify_code(pc, 0, new, false); > +} > + > +/* > + * Turn on the call to ftrace_caller() in instrumented function > + */ > +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) > +{ > + unsigned long pc = rec->ip; > + unsigned int old, new; > + > + old = aarch64_insn_gen_nop(); > + new = aarch64_insn_gen_branch_imm(pc, addr, true); > + > + return ftrace_modify_code(pc, old, new, true); > +} > + > +/* > + * Turn off the call to ftrace_caller() in instrumented function > + */ > +int ftrace_make_nop(struct module *mod, > + struct dyn_ftrace *rec, unsigned long addr) > +{ > + unsigned long pc = rec->ip; > + unsigned int old, new; > + > + old = aarch64_insn_gen_branch_imm(pc, addr, true); > + new = aarch64_insn_gen_nop(); > + > + return ftrace_modify_code(pc, old, new, true); > +} > + > +int __init ftrace_dyn_arch_init(void *data) > +{ > + *(unsigned long *)data = 0; > + > + return 0; > +} > +#endif /* CONFIG_DYNAMIC_FTRACE */ > + > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > /* > * function_graph tracer expects ftrace_return_to_handler() to be called > @@ -61,4 +144,34 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, > return; > } > } > + > +#ifdef CONFIG_DYNAMIC_FTRACE > +/* > + * Turn on/off the call to ftrace_graph_caller() in ftrace_caller() > + * depending on @enable. > + */ > +static int ftrace_modify_graph_caller(bool enable) > +{ > + unsigned long pc = (unsigned long)&ftrace_graph_call; > + unsigned int branch, nop, old, new; > + > + branch = aarch64_insn_gen_branch_imm(pc, > + (unsigned long)ftrace_graph_caller, false); > + nop = aarch64_insn_gen_nop(); > + old = enable ? nop : branch; > + new = enable ? branch : nop; > + > + return ftrace_modify_code(pc, old, new, true); You could rewrite this as: if (enable) return ftrace_modify_code(pc, nop, branch, true); else return ftrace_modify_code(pc, branch, nop, true); which I find easier to read. Will
On Thu, 2014-03-13 at 18:10 +0000, Will Deacon wrote: > > > +#else /* CONFIG_DYNAMIC_FTRACE */ > > +/* > > + * _mcount() is used to build the kernel with -pg option, but all the branch > > + * instructions to _mcount() are replaced to NOP initially at kernel start up, > > + * and later on, NOP to branch to ftrace_caller() when enabled or branch to > > + * NOP when disabled per-function base. > > + */ > > +ENTRY(_mcount) > > + ret > > +ENDPROC(_mcount) > > Judging by your comment then, this should never be called. Is that right? If > so, we could add a BUG-equivalent so we know if we missed an mcount during > patching. Actually, it can be called before the change to nops are done in early boot. This is done very early, but everything before ftrace_init() in init/main.c can still call _mcount. > > + /* > > + * Note: > > + * Due to modules and __init, code can disappear and change, > > + * we need to protect against faulting as well as code changing. > > + * We do this by aarch64_insn_*() which use the probe_kernel_*(). > > + * > > + * No lock is held here because all the modifications are run > > + * through stop_machine(). > > + */ > > + if (validate) { > > + if (aarch64_insn_read((void *)pc, &replaced)) > > + return -EFAULT; > > + > > + if (replaced != old) > > + return -EINVAL; > > + } > > + if (aarch64_insn_patch_text_nosync((void *)pc, new)) > > + return -EPERM; > > I think you're better off propagating the errors here, rather than > overriding them with EFAULT/EINVAL/EPERM. The ftrace generic code expects to see these specific errors. Look at ftrace_bug() in kernel/trace/ftrace.c. > > > + > > + return 0; > > +} > > + > > +/* > > + * Replace tracer function in ftrace_caller() > > + */ > > +int ftrace_update_ftrace_func(ftrace_func_t func) > > +{ > > + unsigned long pc; > > + unsigned int new; > > + > > + pc = (unsigned long)&ftrace_call; > > + new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, true); > > + > > + return ftrace_modify_code(pc, 0, new, false); > > +} > > + > > +/* > > + * Turn on the call to ftrace_caller() in instrumented function > > + */ > > +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) > > +{ > > + unsigned long pc = rec->ip; > > + unsigned int old, new; > > + > > + old = aarch64_insn_gen_nop(); > > + new = aarch64_insn_gen_branch_imm(pc, addr, true); > > + > > + return ftrace_modify_code(pc, old, new, true); > > +} > > + > > +/* > > + * Turn off the call to ftrace_caller() in instrumented function > > + */ > > +int ftrace_make_nop(struct module *mod, > > + struct dyn_ftrace *rec, unsigned long addr) > > +{ > > + unsigned long pc = rec->ip; > > + unsigned int old, new; > > + > > + old = aarch64_insn_gen_branch_imm(pc, addr, true); > > + new = aarch64_insn_gen_nop(); > > + > > + return ftrace_modify_code(pc, old, new, true); > > +} > > + > > +int __init ftrace_dyn_arch_init(void *data) > > +{ > > + *(unsigned long *)data = 0; > > + > > + return 0; > > +} > > +#endif /* CONFIG_DYNAMIC_FTRACE */ > > + > > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > > /* > > * function_graph tracer expects ftrace_return_to_handler() to be called > > @@ -61,4 +144,34 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, > > return; > > } > > } > > + > > +#ifdef CONFIG_DYNAMIC_FTRACE > > +/* > > + * Turn on/off the call to ftrace_graph_caller() in ftrace_caller() > > + * depending on @enable. > > + */ > > +static int ftrace_modify_graph_caller(bool enable) > > +{ > > + unsigned long pc = (unsigned long)&ftrace_graph_call; > > + unsigned int branch, nop, old, new; > > + > > + branch = aarch64_insn_gen_branch_imm(pc, > > + (unsigned long)ftrace_graph_caller, false); > > + nop = aarch64_insn_gen_nop(); > > + old = enable ? nop : branch; > > + new = enable ? branch : nop; > > + > > + return ftrace_modify_code(pc, old, new, true); > > You could rewrite this as: > > if (enable) > return ftrace_modify_code(pc, nop, branch, true); > else > return ftrace_modify_code(pc, branch, nop, true); > > which I find easier to read. Heh, maybe that could be updated in other archs too. I'll have to think about that one. -- Steve
On 03/14/2014 03:10 AM, Will Deacon wrote: > On Thu, Mar 13, 2014 at 10:13:48AM +0000, AKASHI Takahiro wrote: >> This patch allows "dynamic ftrace" if CONFIG_DYNAMIC_FTRACE is enabled. >> Here we can turn on and off tracing dynamically per-function base. >> >> On arm64, this is done by patching single branch instruction to _mcount() >> inserted by gcc -pg option. The branch is replaced to NOP initially at >> kernel start up, and later on, NOP to branch to ftrace_caller() when >> enabled or branch to NOP when disabled. >> Please note that ftrace_caller() is a counterpart of _mcount() in case of >> 'static' ftrace. >> >> More details on architecture specific requirements are described in >> Documentation/trace/ftrace-design.txt. >> >> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> >> --- >> arch/arm64/Kconfig | 1 + >> arch/arm64/include/asm/ftrace.h | 15 +++++ >> arch/arm64/kernel/entry-ftrace.S | 43 +++++++++++++++ >> arch/arm64/kernel/ftrace.c | 113 ++++++++++++++++++++++++++++++++++++++ >> 4 files changed, 172 insertions(+) >> >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >> index 6b3fef6..6954959 100644 >> --- a/arch/arm64/Kconfig >> +++ b/arch/arm64/Kconfig >> @@ -33,6 +33,7 @@ config ARM64 >> select HAVE_DMA_API_DEBUG >> select HAVE_DMA_ATTRS >> select HAVE_DMA_CONTIGUOUS >> + select HAVE_DYNAMIC_FTRACE >> select HAVE_EFFICIENT_UNALIGNED_ACCESS >> select HAVE_FTRACE_MCOUNT_RECORD >> select HAVE_FUNCTION_TRACER >> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h >> index 58ea595..ed5c448 100644 >> --- a/arch/arm64/include/asm/ftrace.h >> +++ b/arch/arm64/include/asm/ftrace.h >> @@ -18,6 +18,21 @@ >> >> #ifndef __ASSEMBLY__ >> extern void _mcount(unsigned long); >> + >> +struct dyn_arch_ftrace { >> + /* No extra data needed for arm64 */ >> +}; >> + >> +extern unsigned long ftrace_graph_call; >> + >> +static inline unsigned long ftrace_call_adjust(unsigned long addr) >> +{ >> + /* >> + * addr is the address of the mcount call instruction. >> + * recordmcount does the necessary offset calculation. >> + */ >> + return addr; >> +} > > You could just as easily implement this as a dummy macro, but I guess it > doesn't matter either way. FYI, all archs define this as an inline function. Leave it as it is. >> #endif /* __ASSEMBLY__ */ >> >> #endif /* __ASM_FTRACE_H */ >> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S >> index 0ac31c8..c0fbe10 100644 >> --- a/arch/arm64/kernel/entry-ftrace.S >> +++ b/arch/arm64/kernel/entry-ftrace.S >> @@ -86,6 +86,7 @@ >> add \reg, \reg, #8 >> .endm >> >> +#ifndef CONFIG_DYNAMIC_FTRACE >> /* >> * void _mcount(unsigned long return_address) >> * @return_address: return address to instrumented function >> @@ -134,6 +135,48 @@ skip_ftrace_call: >> #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ >> ENDPROC(_mcount) >> >> +#else /* CONFIG_DYNAMIC_FTRACE */ >> +/* >> + * _mcount() is used to build the kernel with -pg option, but all the branch >> + * instructions to _mcount() are replaced to NOP initially at kernel start up, >> + * and later on, NOP to branch to ftrace_caller() when enabled or branch to >> + * NOP when disabled per-function base. >> + */ >> +ENTRY(_mcount) >> + ret >> +ENDPROC(_mcount) > > Judging by your comment then, this should never be called. Is that right? If > so, we could add a BUG-equivalent so we know if we missed an mcount during > patching. Steven explained this. >> +/* >> + * void ftrace_caller(unsigned long return_address) >> + * @return_address: return address to instrumented function >> + * >> + * This function is a counterpart of _mcount() in 'static' ftrace, and >> + * makes calls to: >> + * - tracer function to probe instrumented function's entry, >> + * - ftrace_graph_caller to set up an exit hook >> + */ >> +ENTRY(ftrace_caller) >> + mcount_enter >> + >> + mcount_get_pc0 x0 // function's pc >> + mcount_get_lr x1 // function's lr >> + >> + .global ftrace_call >> +ftrace_call: // tracer(pc, lr); >> + nop // This will be replaced with "bl xxx" >> + // where xxx can be any kind of tracer. >> + >> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER >> + .global ftrace_graph_call >> +ftrace_graph_call: // ftrace_graph_caller(); >> + nop // If enabled, this will be replaced >> + // "b ftrace_graph_caller" >> +#endif >> + >> + mcount_exit >> +ENDPROC(ftrace_caller) >> +#endif /* CONFIG_DYNAMIC_FTRACE */ >> + >> ENTRY(ftrace_stub) >> ret >> ENDPROC(ftrace_stub) >> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c >> index a559ab8..8c26476 100644 >> --- a/arch/arm64/kernel/ftrace.c >> +++ b/arch/arm64/kernel/ftrace.c >> @@ -17,6 +17,89 @@ >> #include <asm/ftrace.h> >> #include <asm/insn.h> >> >> +#ifdef CONFIG_DYNAMIC_FTRACE >> +/* >> + * Replace a single instruction, which may be a branch or NOP. >> + * If @validate == true, a replaced instruction is checked against 'old'. >> + */ >> +static int ftrace_modify_code(unsigned long pc, unsigned int old, >> + unsigned int new, bool validate) >> +{ >> + unsigned int replaced; > > u32 is a bit clearer for instructions. Fix it. >> + /* >> + * Note: >> + * Due to modules and __init, code can disappear and change, >> + * we need to protect against faulting as well as code changing. >> + * We do this by aarch64_insn_*() which use the probe_kernel_*(). >> + * >> + * No lock is held here because all the modifications are run >> + * through stop_machine(). >> + */ >> + if (validate) { >> + if (aarch64_insn_read((void *)pc, &replaced)) >> + return -EFAULT; >> + >> + if (replaced != old) >> + return -EINVAL; >> + } >> + if (aarch64_insn_patch_text_nosync((void *)pc, new)) >> + return -EPERM; > > I think you're better off propagating the errors here, rather than > overriding them with EFAULT/EINVAL/EPERM. Steven explained this. >> + >> + return 0; >> +} >> + >> +/* >> + * Replace tracer function in ftrace_caller() >> + */ >> +int ftrace_update_ftrace_func(ftrace_func_t func) >> +{ >> + unsigned long pc; >> + unsigned int new; >> + >> + pc = (unsigned long)&ftrace_call; >> + new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, true); >> + >> + return ftrace_modify_code(pc, 0, new, false); >> +} >> + >> +/* >> + * Turn on the call to ftrace_caller() in instrumented function >> + */ >> +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) >> +{ >> + unsigned long pc = rec->ip; >> + unsigned int old, new; >> + >> + old = aarch64_insn_gen_nop(); >> + new = aarch64_insn_gen_branch_imm(pc, addr, true); >> + >> + return ftrace_modify_code(pc, old, new, true); >> +} >> + >> +/* >> + * Turn off the call to ftrace_caller() in instrumented function >> + */ >> +int ftrace_make_nop(struct module *mod, >> + struct dyn_ftrace *rec, unsigned long addr) >> +{ >> + unsigned long pc = rec->ip; >> + unsigned int old, new; >> + >> + old = aarch64_insn_gen_branch_imm(pc, addr, true); >> + new = aarch64_insn_gen_nop(); >> + >> + return ftrace_modify_code(pc, old, new, true); >> +} >> + >> +int __init ftrace_dyn_arch_init(void *data) >> +{ >> + *(unsigned long *)data = 0; >> + >> + return 0; >> +} >> +#endif /* CONFIG_DYNAMIC_FTRACE */ >> + >> #ifdef CONFIG_FUNCTION_GRAPH_TRACER >> /* >> * function_graph tracer expects ftrace_return_to_handler() to be called >> @@ -61,4 +144,34 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, >> return; >> } >> } >> + >> +#ifdef CONFIG_DYNAMIC_FTRACE >> +/* >> + * Turn on/off the call to ftrace_graph_caller() in ftrace_caller() >> + * depending on @enable. >> + */ >> +static int ftrace_modify_graph_caller(bool enable) >> +{ >> + unsigned long pc = (unsigned long)&ftrace_graph_call; >> + unsigned int branch, nop, old, new; >> + >> + branch = aarch64_insn_gen_branch_imm(pc, >> + (unsigned long)ftrace_graph_caller, false); >> + nop = aarch64_insn_gen_nop(); >> + old = enable ? nop : branch; >> + new = enable ? branch : nop; >> + >> + return ftrace_modify_code(pc, old, new, true); > > You could rewrite this as: > > if (enable) > return ftrace_modify_code(pc, nop, branch, true); > else > return ftrace_modify_code(pc, branch, nop, true); > > which I find easier to read. Yep, fix it. -Takahiro AKASHI > Will >
Thank you for you clarification, Steven. -Takahiro AKASHI On 03/14/2014 03:33 AM, Steven Rostedt wrote: > On Thu, 2014-03-13 at 18:10 +0000, Will Deacon wrote: >> >>> +#else /* CONFIG_DYNAMIC_FTRACE */ >>> +/* >>> + * _mcount() is used to build the kernel with -pg option, but all the branch >>> + * instructions to _mcount() are replaced to NOP initially at kernel start up, >>> + * and later on, NOP to branch to ftrace_caller() when enabled or branch to >>> + * NOP when disabled per-function base. >>> + */ >>> +ENTRY(_mcount) >>> + ret >>> +ENDPROC(_mcount) >> >> Judging by your comment then, this should never be called. Is that right? If >> so, we could add a BUG-equivalent so we know if we missed an mcount during >> patching. > > Actually, it can be called before the change to nops are done in early > boot. This is done very early, but everything before ftrace_init() in > init/main.c can still call _mcount. > > >>> + /* >>> + * Note: >>> + * Due to modules and __init, code can disappear and change, >>> + * we need to protect against faulting as well as code changing. >>> + * We do this by aarch64_insn_*() which use the probe_kernel_*(). >>> + * >>> + * No lock is held here because all the modifications are run >>> + * through stop_machine(). >>> + */ >>> + if (validate) { >>> + if (aarch64_insn_read((void *)pc, &replaced)) >>> + return -EFAULT; >>> + >>> + if (replaced != old) >>> + return -EINVAL; >>> + } >>> + if (aarch64_insn_patch_text_nosync((void *)pc, new)) >>> + return -EPERM; >> >> I think you're better off propagating the errors here, rather than >> overriding them with EFAULT/EINVAL/EPERM. > > The ftrace generic code expects to see these specific errors. Look at > ftrace_bug() in kernel/trace/ftrace.c. > >> >>> + >>> + return 0; >>> +} >>> + >>> +/* >>> + * Replace tracer function in ftrace_caller() >>> + */ >>> +int ftrace_update_ftrace_func(ftrace_func_t func) >>> +{ >>> + unsigned long pc; >>> + unsigned int new; >>> + >>> + pc = (unsigned long)&ftrace_call; >>> + new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, true); >>> + >>> + return ftrace_modify_code(pc, 0, new, false); >>> +} >>> + >>> +/* >>> + * Turn on the call to ftrace_caller() in instrumented function >>> + */ >>> +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) >>> +{ >>> + unsigned long pc = rec->ip; >>> + unsigned int old, new; >>> + >>> + old = aarch64_insn_gen_nop(); >>> + new = aarch64_insn_gen_branch_imm(pc, addr, true); >>> + >>> + return ftrace_modify_code(pc, old, new, true); >>> +} >>> + >>> +/* >>> + * Turn off the call to ftrace_caller() in instrumented function >>> + */ >>> +int ftrace_make_nop(struct module *mod, >>> + struct dyn_ftrace *rec, unsigned long addr) >>> +{ >>> + unsigned long pc = rec->ip; >>> + unsigned int old, new; >>> + >>> + old = aarch64_insn_gen_branch_imm(pc, addr, true); >>> + new = aarch64_insn_gen_nop(); >>> + >>> + return ftrace_modify_code(pc, old, new, true); >>> +} >>> + >>> +int __init ftrace_dyn_arch_init(void *data) >>> +{ >>> + *(unsigned long *)data = 0; >>> + >>> + return 0; >>> +} >>> +#endif /* CONFIG_DYNAMIC_FTRACE */ >>> + >>> #ifdef CONFIG_FUNCTION_GRAPH_TRACER >>> /* >>> * function_graph tracer expects ftrace_return_to_handler() to be called >>> @@ -61,4 +144,34 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, >>> return; >>> } >>> } >>> + >>> +#ifdef CONFIG_DYNAMIC_FTRACE >>> +/* >>> + * Turn on/off the call to ftrace_graph_caller() in ftrace_caller() >>> + * depending on @enable. >>> + */ >>> +static int ftrace_modify_graph_caller(bool enable) >>> +{ >>> + unsigned long pc = (unsigned long)&ftrace_graph_call; >>> + unsigned int branch, nop, old, new; >>> + >>> + branch = aarch64_insn_gen_branch_imm(pc, >>> + (unsigned long)ftrace_graph_caller, false); >>> + nop = aarch64_insn_gen_nop(); >>> + old = enable ? nop : branch; >>> + new = enable ? branch : nop; >>> + >>> + return ftrace_modify_code(pc, old, new, true); >> >> You could rewrite this as: >> >> if (enable) >> return ftrace_modify_code(pc, nop, branch, true); >> else >> return ftrace_modify_code(pc, branch, nop, true); >> >> which I find easier to read. > > Heh, maybe that could be updated in other archs too. I'll have to think > about that one. > > -- Steve > >
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 6b3fef6..6954959 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -33,6 +33,7 @@ config ARM64 select HAVE_DMA_API_DEBUG select HAVE_DMA_ATTRS select HAVE_DMA_CONTIGUOUS + select HAVE_DYNAMIC_FTRACE select HAVE_EFFICIENT_UNALIGNED_ACCESS select HAVE_FTRACE_MCOUNT_RECORD select HAVE_FUNCTION_TRACER diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h index 58ea595..ed5c448 100644 --- a/arch/arm64/include/asm/ftrace.h +++ b/arch/arm64/include/asm/ftrace.h @@ -18,6 +18,21 @@ #ifndef __ASSEMBLY__ extern void _mcount(unsigned long); + +struct dyn_arch_ftrace { + /* No extra data needed for arm64 */ +}; + +extern unsigned long ftrace_graph_call; + +static inline unsigned long ftrace_call_adjust(unsigned long addr) +{ + /* + * addr is the address of the mcount call instruction. + * recordmcount does the necessary offset calculation. + */ + return addr; +} #endif /* __ASSEMBLY__ */ #endif /* __ASM_FTRACE_H */ diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S index 0ac31c8..c0fbe10 100644 --- a/arch/arm64/kernel/entry-ftrace.S +++ b/arch/arm64/kernel/entry-ftrace.S @@ -86,6 +86,7 @@ add \reg, \reg, #8 .endm +#ifndef CONFIG_DYNAMIC_FTRACE /* * void _mcount(unsigned long return_address) * @return_address: return address to instrumented function @@ -134,6 +135,48 @@ skip_ftrace_call: #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ ENDPROC(_mcount) +#else /* CONFIG_DYNAMIC_FTRACE */ +/* + * _mcount() is used to build the kernel with -pg option, but all the branch + * instructions to _mcount() are replaced to NOP initially at kernel start up, + * and later on, NOP to branch to ftrace_caller() when enabled or branch to + * NOP when disabled per-function base. + */ +ENTRY(_mcount) + ret +ENDPROC(_mcount) + +/* + * void ftrace_caller(unsigned long return_address) + * @return_address: return address to instrumented function + * + * This function is a counterpart of _mcount() in 'static' ftrace, and + * makes calls to: + * - tracer function to probe instrumented function's entry, + * - ftrace_graph_caller to set up an exit hook + */ +ENTRY(ftrace_caller) + mcount_enter + + mcount_get_pc0 x0 // function's pc + mcount_get_lr x1 // function's lr + + .global ftrace_call +ftrace_call: // tracer(pc, lr); + nop // This will be replaced with "bl xxx" + // where xxx can be any kind of tracer. + +#ifdef CONFIG_FUNCTION_GRAPH_TRACER + .global ftrace_graph_call +ftrace_graph_call: // ftrace_graph_caller(); + nop // If enabled, this will be replaced + // "b ftrace_graph_caller" +#endif + + mcount_exit +ENDPROC(ftrace_caller) +#endif /* CONFIG_DYNAMIC_FTRACE */ + ENTRY(ftrace_stub) ret ENDPROC(ftrace_stub) diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index a559ab8..8c26476 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -17,6 +17,89 @@ #include <asm/ftrace.h> #include <asm/insn.h> +#ifdef CONFIG_DYNAMIC_FTRACE +/* + * Replace a single instruction, which may be a branch or NOP. + * If @validate == true, a replaced instruction is checked against 'old'. + */ +static int ftrace_modify_code(unsigned long pc, unsigned int old, + unsigned int new, bool validate) +{ + unsigned int replaced; + + /* + * Note: + * Due to modules and __init, code can disappear and change, + * we need to protect against faulting as well as code changing. + * We do this by aarch64_insn_*() which use the probe_kernel_*(). + * + * No lock is held here because all the modifications are run + * through stop_machine(). + */ + if (validate) { + if (aarch64_insn_read((void *)pc, &replaced)) + return -EFAULT; + + if (replaced != old) + return -EINVAL; + } + if (aarch64_insn_patch_text_nosync((void *)pc, new)) + return -EPERM; + + return 0; +} + +/* + * Replace tracer function in ftrace_caller() + */ +int ftrace_update_ftrace_func(ftrace_func_t func) +{ + unsigned long pc; + unsigned int new; + + pc = (unsigned long)&ftrace_call; + new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, true); + + return ftrace_modify_code(pc, 0, new, false); +} + +/* + * Turn on the call to ftrace_caller() in instrumented function + */ +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) +{ + unsigned long pc = rec->ip; + unsigned int old, new; + + old = aarch64_insn_gen_nop(); + new = aarch64_insn_gen_branch_imm(pc, addr, true); + + return ftrace_modify_code(pc, old, new, true); +} + +/* + * Turn off the call to ftrace_caller() in instrumented function + */ +int ftrace_make_nop(struct module *mod, + struct dyn_ftrace *rec, unsigned long addr) +{ + unsigned long pc = rec->ip; + unsigned int old, new; + + old = aarch64_insn_gen_branch_imm(pc, addr, true); + new = aarch64_insn_gen_nop(); + + return ftrace_modify_code(pc, old, new, true); +} + +int __init ftrace_dyn_arch_init(void *data) +{ + *(unsigned long *)data = 0; + + return 0; +} +#endif /* CONFIG_DYNAMIC_FTRACE */ + #ifdef CONFIG_FUNCTION_GRAPH_TRACER /* * function_graph tracer expects ftrace_return_to_handler() to be called @@ -61,4 +144,34 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, return; } } + +#ifdef CONFIG_DYNAMIC_FTRACE +/* + * Turn on/off the call to ftrace_graph_caller() in ftrace_caller() + * depending on @enable. + */ +static int ftrace_modify_graph_caller(bool enable) +{ + unsigned long pc = (unsigned long)&ftrace_graph_call; + unsigned int branch, nop, old, new; + + branch = aarch64_insn_gen_branch_imm(pc, + (unsigned long)ftrace_graph_caller, false); + nop = aarch64_insn_gen_nop(); + old = enable ? nop : branch; + new = enable ? branch : nop; + + return ftrace_modify_code(pc, old, new, true); +} + +int ftrace_enable_ftrace_graph_caller(void) +{ + return ftrace_modify_graph_caller(true); +} + +int ftrace_disable_ftrace_graph_caller(void) +{ + return ftrace_modify_graph_caller(false); +} +#endif /* CONFIG_DYNAMIC_FTRACE */ #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
This patch allows "dynamic ftrace" if CONFIG_DYNAMIC_FTRACE is enabled. Here we can turn on and off tracing dynamically per-function base. On arm64, this is done by patching single branch instruction to _mcount() inserted by gcc -pg option. The branch is replaced to NOP initially at kernel start up, and later on, NOP to branch to ftrace_caller() when enabled or branch to NOP when disabled. Please note that ftrace_caller() is a counterpart of _mcount() in case of 'static' ftrace. More details on architecture specific requirements are described in Documentation/trace/ftrace-design.txt. Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/ftrace.h | 15 +++++ arch/arm64/kernel/entry-ftrace.S | 43 +++++++++++++++ arch/arm64/kernel/ftrace.c | 113 ++++++++++++++++++++++++++++++++++++++ 4 files changed, 172 insertions(+)