On Mon, 10 Feb 2014 16:03:21 +0100 Arnd Bergmann arnd@arndb.de wrote:
On Friday 07 February 2014, AKASHI Takahiro wrote:
@@ -0,0 +1,23 @@
+#ifdef CONFIG_FUNCTION_TRACER +#define MCOUNT_ADDR ((unsigned long)_mcount) +#define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */
+#ifndef __ASSEMBLY__ +extern void _mcount(unsigned long); +#endif /* __ASSEMBLY__ */ +#endif /* CONFIG_FUNCTION_TRACER */
We generally like to have as few #ifdef as possible, and I think the #ifdef CONFIG_FUNCTION_TRACER here is not needed.
+#endif /* __ASM_FTRACE_H */ diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index 2d4554b..ca921fb 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -5,6 +5,11 @@ CPPFLAGS_vmlinux.lds := -DTEXT_OFFSET=$(TEXT_OFFSET) AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) +ifdef CONFIG_FUNCTION_TRACER +CFLAGS_REMOVE_ftrace.o = -pg +CFLAGS_REMOVE_insn.o = -pg +endif
Same here. It never hurts to have the CFLAGS_REMOVE_* statements here, since you will not want to build these files for profiling.
I agree to this. I will admit, this was probably just a copy from my code as I did the same in other Makefiles. I think I added the ifdef statements as more of documenting what the REMOVE was for, when ftrace was just being added to the kernel, and not well known.
I should probably go back and remove the ifdef's from other Makefiles too.
A comment about what the -pg is for wouldn't hurt, though:
# For files that should not have any function tracing done to them, # we must remove the -pg flag.
Something like that.
diff --git a/arch/arm64/kernel/arm64ksyms.c b/arch/arm64/kernel/arm64ksyms.c index 338b568..7f0512f 100644 --- a/arch/arm64/kernel/arm64ksyms.c +++ b/arch/arm64/kernel/arm64ksyms.c @@ -56,3 +56,7 @@ EXPORT_SYMBOL(clear_bit); EXPORT_SYMBOL(test_and_clear_bit); EXPORT_SYMBOL(change_bit); EXPORT_SYMBOL(test_and_change_bit);
+#ifdef CONFIG_FUNCTION_TRACER +EXPORT_SYMBOL(_mcount); +#endif
This one is clearly needed of course.
+/*
- Gcc with -pg will put the following code in the beginning of each function:
mov x0, x30
bl _mcount
- [function's body ...]
- "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
- ftrace is enabled.
Unrelated to your patch, I have run into problems with this on arm32, maybe someone on Cc to this mail has an idea what to do about it:
If I build a large "randconfig" kernel or "allyesconfig", the kernel image size exceeds 32MB, which means I can no longer link callers with a 26 bit signed immediate argument like the "bl _mcount" here. For any other function calls, "gcc -mlong-calls" can be used to work around this, but this particular instance is created by inserting assembly statements into the output without considering the long-call options. Is there a way to get the kernel to link anyway?
I wonder if we play linker games and move the _mcount and ftrace_caller and friends into the middle of the kernel? If it is only missing it by a slight overflow of a 32bit jump, then maybe moving it will work.
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
Here, again, you an remove the #ifdef by making the entire file built only for CONFIG_FUNCTION_GRAPH_TRACER.
Interesting. Other archs (at least x86 and powerpc) required this file for function tracing too. Seems this is only needed for function graph tracer.
-- Steve