The main change is to just use paca->kernel_toc, rather than a branch to +4 and mflr etc. That makes the code simpler and should also perform better. There was also a sequence after ftrace_call() where we load from pt_regs->nip, move to LR, then a few instructions later load from LRSAVE and move to LR. Instead I think we want to put pt_regs->nip into CTR and branch to it later. We also rework some of the SPR loads to hopefully speed them up a bit. Also comment the asm much more, to hopefully make it clearer. Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> --- arch/powerpc/kernel/entry_64.S | 94 ++++++++++++++++++++++++++++-------------- 1 file changed, 62 insertions(+), 32 deletions(-) Squash. diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index 149b659a25d9..f347f50024b8 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -1171,65 +1171,98 @@ _GLOBAL(ftrace_graph_stub) mtlr r0 addi r1, r1, 112 #else +/* + * + * ftrace_caller() is the function that replaces _mcount() when ftrace is + * active. + * + * We arrive here after a function A calls function B, and we are the trace + * function for B. When we enter r1 points to A's stack frame, B has not yet + * had a chance to allocate one yet. + * + * Additionally r2 may point either to the TOC for A, or B, depending on + * whether B did a TOC setup sequence before calling us. + * + * On entry the LR points back to the _mcount() call site, and r0 holds the + * saved LR as it was on entry to B, ie. the original return address at the + * call site in A. + * + * Our job is to save the register state into a struct pt_regs (on the stack) + * and then arrange for the ftrace function to be called. + */ _GLOBAL(ftrace_caller) + /* Save the original return address in A's stack frame */ std r0,LRSAVE(r1) -#if defined(_CALL_ELF) && _CALL_ELF == 2 - mflr r0 - bl 2f -2: mflr r12 - mtlr r0 - mr r0,r2 /* save callee's TOC */ - addis r2,r12,(.TOC.-ftrace_caller-12)@ha - addi r2,r2,(.TOC.-ftrace_caller-12)@l -#else - mr r0,r2 -#endif - ld r12,LRSAVE(r1) /* get caller's address */ + /* Create our stack frame + pt_regs */ stdu r1,-SWITCH_FRAME_SIZE(r1) - std r12, _LINK(r1) + /* Save all gprs to pt_regs */ SAVE_8GPRS(0,r1) - std r0, 24(r1) /* save TOC */ SAVE_8GPRS(8,r1) SAVE_8GPRS(16,r1) SAVE_8GPRS(24,r1) + /* Load special regs for save below */ + mfmsr r8 + mfctr r9 + mfxer r10 + mfcr r11 + + /* Get the _mcount() call site out of LR */ + mflr r7 + /* Save it as pt_regs->nip & pt_regs->link */ + std r7, _NIP(r1) + std r7, _LINK(r1) + + /* Save callee's TOC in the ABI compliant location */ + std r2, 24(r1) + ld r2,PACATOC(r13) /* get kernel TOC in r2 */ + addis r3,r2,function_trace_op@toc@ha addi r3,r3,function_trace_op@toc@l ld r5,0(r3) - mflr r3 - std r3, _NIP(r1) - std r3, 16(r1) - subi r3, r3, MCOUNT_INSN_SIZE - mfmsr r4 - std r4, _MSR(r1) - mfctr r4 - std r4, _CTR(r1) - mfxer r4 - std r4, _XER(r1) - mr r4, r12 + /* Calculate ip from nip-4 into r3 for call below */ + subi r3, r7, MCOUNT_INSN_SIZE + + /* Put the original return address in r4 as parent_ip */ + mr r4, r0 + + /* Save special regs */ + std r8, _MSR(r1) + std r9, _CTR(r1) + std r10, _XER(r1) + std r11, _CCR(r1) + + /* Load &pt_regs in r6 for call below */ addi r6, r1 ,STACK_FRAME_OVERHEAD + /* ftrace_call(r3, r4, r5, r6) */ .globl ftrace_call ftrace_call: bl ftrace_stub nop + /* Load ctr with the possibly modified NIP */ ld r3, _NIP(r1) - mtlr r3 + mtctr r3 + /* Restore gprs */ REST_8GPRS(0,r1) REST_8GPRS(8,r1) REST_8GPRS(16,r1) REST_8GPRS(24,r1) + /* Restore callee's TOC */ + ld r2, 24(r1) + + /* Pop our stack frame */ addi r1, r1, SWITCH_FRAME_SIZE - ld r12, LRSAVE(r1) /* get caller's address */ - mtlr r12 - mr r2,r0 /* restore callee's TOC */ + /* Restore original LR for return to B */ + ld r0, LRSAVE(r1) + mtlr r0 #ifdef CONFIG_FUNCTION_GRAPH_TRACER stdu r1, -112(r1) @@ -1240,9 +1273,6 @@ _GLOBAL(ftrace_graph_stub) addi r1, r1, 112 #endif - mflr r0 /* move this LR to CTR */ - mtctr r0 - ld r0,LRSAVE(r1) /* restore callee's lr at _mcount site */ mtlr r0 bctr /* jump after _mcount site */ -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
