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