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 <m...@ellerman.id.au>
---
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
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