From 7326c4e567b50e689d13c04d58aeffa515277ebb Mon Sep 17 00:00:00 2001 From: Wu Zhangjin Date: Fri, 20 Nov 2009 20:34:38 +0800 Subject: MIPS: Tracing: Make function graph tracer work with -mmcount-ra-address That thread "MIPS: Add option to pass return address location to _mcount" from "David Daney " have added a new option -mmcount-ra-address to gcc(4.5) for MIPS to transfer the location of the return address to _mcount. Benefit from this new feature, function graph tracer on MIPS will be easier and safer to hijack the return address of the kernel function, which will save some overhead and make the whole thing more reliable. In this patch, at first, try to enable the option -mmcount-ra-address in arch/mips/Makefile with cc-option, if gcc support it, it will be enabled, otherwise, no side effect. and then, we need to support this new option of gcc 4.5 and also support the old gcc versions. with _mcount in the old gcc versions, it's not easy to get the location of return address(tracing: add function graph tracer support for MIPS), so, we do it in a C function: ftrace_get_parent_addr(ftrace.c), but with -mmcount-ra-address, only several instructions need to get what we want, so, I put into asm(mcount.S). and also, as the $12(t0) is used by -mmcount-ra-address for transferring the localtion of return address to _mcount, we need to save it into the stack and restore it when enabled dynamic function tracer, 'Cause we have called "ftrace_call" before "ftrace_graph_caller", which may destroy $12(t0). (Thanks to David for providing that -mcount-ra-address and giving the idea of KBUILD_MCOUNT_RA_ADDRESS, both of them have made the whole thing more beautiful!) Signed-off-by: Wu Zhangjin Cc: Steven Rostedt Cc: Nicholas Mc Guire Cc: zhangfx@lemote.com Cc: Wu Zhangjin Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org Cc: linux-mips@linux-mips.org Patchwork: http://patchwork.linux-mips.org/patch/681/ Signed-off-by: Ralf Baechle --- arch/mips/kernel/ftrace.c | 24 +++++++++++++++++------- arch/mips/kernel/mcount.S | 14 ++++++++++++++ 2 files changed, 31 insertions(+), 7 deletions(-) (limited to 'arch/mips/kernel') diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c index e363fc69aabd..68b067040d8b 100644 --- a/arch/mips/kernel/ftrace.c +++ b/arch/mips/kernel/ftrace.c @@ -148,6 +148,7 @@ int ftrace_disable_ftrace_graph_caller(void) #endif /* !CONFIG_DYNAMIC_FTRACE */ +#ifndef KBUILD_MCOUNT_RA_ADDRESS #define S_RA_SP (0xafbf << 16) /* s{d,w} ra, offset(sp) */ #define S_R_SP (0xafb0 << 16) /* s{d,w} R, offset(sp) */ #define OFFSET_MASK 0xffff /* stack offset range: 0 ~ PT_SIZE */ @@ -201,6 +202,8 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr, return 0; } +#endif + /* * Hook the return address and push it in the stack of return addrs * in current thread info. @@ -218,19 +221,26 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, return; /* "parent" is the stack address saved the return address of the caller - * of _mcount, for a leaf function not save the return address in the - * stack address, so, we "emulate" one in _mcount's stack space, and - * hijack it directly, but for a non-leaf function, it will save the - * return address to the its stack space, so, we can not hijack the - * "parent" directly, but need to find the real stack address, + * of _mcount. + * + * if the gcc < 4.5, a leaf function does not save the return address + * in the stack address, so, we "emulate" one in _mcount's stack space, + * and hijack it directly, but for a non-leaf function, it save the + * return address to the its own stack space, we can not hijack it + * directly, but need to find the real stack address, * ftrace_get_parent_addr() does it! + * + * if gcc>= 4.5, with the new -mmcount-ra-address option, for a + * non-leaf function, the location of the return address will be saved + * to $12 for us, and for a leaf function, only put a zero into $12. we + * do it in ftrace_graph_caller of mcount.S. */ /* old = *parent; */ safe_load_stack(old, parent, faulted); if (unlikely(faulted)) goto out; - +#ifndef KBUILD_MCOUNT_RA_ADDRESS parent = (unsigned long *)ftrace_get_parent_addr(self_addr, old, (unsigned long)parent, fp); @@ -238,7 +248,7 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, * ra, stop function graph tracer and return */ if (parent == 0) goto out; - +#endif /* *parent = return_hooker; */ safe_store_stack(return_hooker, parent, faulted); if (unlikely(faulted)) diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S index 522e91c688fc..0a9cfdb271dd 100644 --- a/arch/mips/kernel/mcount.S +++ b/arch/mips/kernel/mcount.S @@ -70,6 +70,9 @@ _mcount: nop MCOUNT_SAVE_REGS +#ifdef KBUILD_MCOUNT_RA_ADDRESS + PTR_S t0, PT_R12(sp) /* t0 saved the location of the return address(at) by -mmcount-ra-address */ +#endif move a0, ra /* arg1: next ip, selfaddr */ .globl ftrace_call @@ -133,11 +136,22 @@ ftrace_stub: NESTED(ftrace_graph_caller, PT_SIZE, ra) #ifdef CONFIG_DYNAMIC_FTRACE PTR_L a1, PT_R31(sp) /* load the original ra from the stack */ +#ifdef KBUILD_MCOUNT_RA_ADDRESS + PTR_L t0, PT_R12(sp) /* load the original t0 from the stack */ +#endif #else MCOUNT_SAVE_REGS move a1, ra /* arg2: next ip, selfaddr */ #endif + +#ifdef KBUILD_MCOUNT_RA_ADDRESS + bnez t0, 1f /* non-leaf func: t0 saved the location of the return address */ + nop + PTR_LA t0, PT_R1(sp) /* leaf func: get the location of at(old ra) from our own stack */ +1: move a0, t0 /* arg1: the location of the return address */ +#else PTR_LA a0, PT_R1(sp) /* arg1: &AT -> a0 */ +#endif jal prepare_ftrace_return #ifdef CONFIG_FRAME_POINTER move a2, fp /* arg3: frame pointer */ -- cgit v1.2.3