On 25/02/16 01:28, Michael Ellerman wrote: > 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 */ Reviewed-by: Balbir Singh <bsingharora@xxxxxxxxx> -- 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
