[PATCH 04/10] ARM: ftrace: allow building without frame pointers
From: Frederic Weisbecker <hidden>
Date: 2010-02-22 19:05:27
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On Sun, Feb 14, 2010 at 01:18:32AM +0530, Rabin Vincent wrote:
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With a new enough GCC, ARM function tracing can be supported without the need for frame pointers. This is essential for Thumb-2 support, since frame pointers aren't available then. Signed-off-by: Rabin Vincent <redacted> --- arch/arm/Kconfig.debug | 5 +++++ arch/arm/kernel/armksyms.c | 2 ++ arch/arm/kernel/entry-common.S | 7 +++++++ kernel/trace/Kconfig | 2 +- 4 files changed, 15 insertions(+), 1 deletions(-)diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug index 5cb9326..5501253 100644 --- a/arch/arm/Kconfig.debug +++ b/arch/arm/Kconfig.debug@@ -27,6 +27,11 @@ config ARM_UNWIND the performance is not affected. Currently, this feature only works with EABI compilers. If unsure say Y. +config OLD_MCOUNT + bool + depends on FUNCTION_TRACER && FRAME_POINTER + default y +
Btw, you described that mcount is used in some gcc versions and __gnu_mcount_nc in newers. Shouldn't we have a gcc version dependency here? (not sure we can do this from Kconfig though).
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config DEBUG_USER bool "Verbose user fault messages" helpdiff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c index 8214bfe..e5e1e53 100644 --- a/arch/arm/kernel/armksyms.c +++ b/arch/arm/kernel/armksyms.c@@ -165,6 +165,8 @@ EXPORT_SYMBOL(_find_next_bit_be); #endif #ifdef CONFIG_FUNCTION_TRACER +#ifdef CONFIG_OLD_MCOUNT EXPORT_SYMBOL(mcount); +#endif EXPORT_SYMBOL(__gnu_mcount_nc); #endifdiff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S index d412d7c..c98e3a3 100644 --- a/arch/arm/kernel/entry-common.S +++ b/arch/arm/kernel/entry-common.S@@ -169,6 +169,12 @@ gnu_trace: ldmia sp!, {r0-r3, ip, lr} mov pc, ip +#ifdef CONFIG_OLD_MCOUNT +/* + * This is under an ifdef in order to force link-time errors for people trying + * to build with !FRAME_POINTER with a GCC which doesn't use the new-style + * mcount. + */ ENTRY(mcount) stmdb sp!, {r0-r3, lr} ldr r0, =ftrace_trace_function@@ -187,6 +193,7 @@ trace: mov pc, r2 ldr lr, [fp, #-4] @ restore lr ldmia sp!, {r0-r3, pc} +#endif #endif /* CONFIG_DYNAMIC_FTRACE */diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 6c22d8a..7468ffe 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig@@ -126,7 +126,7 @@ if FTRACE config FUNCTION_TRACER bool "Kernel Function Tracer" depends on HAVE_FUNCTION_TRACER - select FRAME_POINTER + select FRAME_POINTER if (!ARM_UNWIND)
So, if I understand well. If people have ARM_UNWIND but FUNCTION_TRACER, it might crash at link time in case they don't have a recent enough gcc version to support the new -pg style? That doesn't look good. Ideally, we need HAVE_FUNCTION_TRACER to be enabled in arm only if (old gcc && frame pointers) || new gcc And then, we need config OLD_MCOUNT: old gcc && FUNCTION_TRACER and config NEW_MCOUNT: new gcc && FUNCTION_TRACER so that we can selectively build mcount or __gnu_mcount_nc. Hmm, I fear we can't check gcc version from Kconfig, as I'm grepping on Kconfig files...