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.aka...@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. 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