From: Wu Zhangjin <wuzhangjin@xxxxxxxxx> As the doc[1] of gcc-4.5 shows, the -mmcount-ra-address uses register $12 to transfer the stack offset of the return address to the _mcount function. in 64bit kernel, $12 is t0, but in 32bit kernel, it is t4, so, we need to use $12 instead of t0 here to cover the 64bit and 32bit support. [1] Gcc doc: MIPS Options http://gcc.gnu.org/onlinedocs/gcc/MIPS-Options.html Changes from old revision: o Apply the feedback from David Daney: define a macro MCOUNT_RA_ADDRESS_REG instead of the magic number $12 Signed-off-by: Wu Zhangjin <wuzhangjin@xxxxxxxxx> --- arch/mips/kernel/mcount.S | 12 +++++++++--- 1 files changed, 9 insertions(+), 3 deletions(-) diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S index 9a029d4..6bfcb7a 100644 --- a/arch/mips/kernel/mcount.S +++ b/arch/mips/kernel/mcount.S @@ -57,6 +57,12 @@ move ra, AT .endm +/* + * The -mmcount-ra-address option of gcc 4.5 uses register $12 to pass + * the location of the parent's return address. + */ +#define MCOUNT_RA_ADDRESS_REG $12 + #ifdef CONFIG_DYNAMIC_FTRACE NESTED(ftrace_caller, PT_SIZE, ra) @@ -70,7 +76,7 @@ _mcount: MCOUNT_SAVE_REGS #ifdef KBUILD_MCOUNT_RA_ADDRESS - PTR_S t0, PT_R12(sp) /* save location of parent's return address */ + PTR_S MCOUNT_RA_ADDRESS_REG, PT_R12(sp) #endif move a0, ra /* arg1: self return address */ @@ -142,9 +148,9 @@ NESTED(ftrace_graph_caller, PT_SIZE, ra) #ifdef CONFIG_DYNAMIC_FTRACE PTR_L a0, PT_R12(sp) #else - move a0, t0 + move a0, MCOUNT_RA_ADDRESS_REG #endif - bnez a0, 1f /* non-leaf func: stored in t0 */ + bnez a0, 1f /* non-leaf func: stored in MCOUNT_RA_ADDRESS_REG */ nop #endif PTR_LA a0, PT_R1(sp) /* leaf func: the location in current stack */ -- 1.7.0.4
