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Subject[PATCH v3 2/5] powerpc: ftrace: restore LR from pt_regs
Date
Pass the real LR to the ftrace handler. This is needed for
KPROBES_ON_FTRACE for the pre handlers.

Also, with KPROBES_ON_FTRACE, the link register may be updated by the
pre handlers or by a registed kretprobe. Honor updated LR by restoring
it from pt_regs, rather than from the stack save area.

Live patch and function graph continue to work fine with this change.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
arch/powerpc/kernel/entry_64.S | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 8fd8718722a1..744b2f91444a 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -1248,9 +1248,10 @@ _GLOBAL(ftrace_caller)

/* Get the _mcount() call site out of LR */
mflr r7
- /* Save it as pt_regs->nip & pt_regs->link */
+ /* Save it as pt_regs->nip */
std r7, _NIP(r1)
- std r7, _LINK(r1)
+ /* Save the read LR in pt_regs->link */
+ std r0, _LINK(r1)

/* Save callee's TOC in the ABI compliant location */
std r2, 24(r1)
@@ -1297,16 +1298,16 @@ ftrace_call:
REST_8GPRS(16,r1)
REST_8GPRS(24,r1)

+ /* Restore possibly modified LR */
+ ld r0, _LINK(r1)
+ mtlr r0
+
/* Restore callee's TOC */
ld r2, 24(r1)

/* Pop our stack frame */
addi r1, r1, SWITCH_FRAME_SIZE

- /* Restore original LR for return to B */
- ld r0, LRSAVE(r1)
- mtlr r0
-
#ifdef CONFIG_LIVEPATCH
/* Based on the cmpd above, if the NIP was altered handle livepatch */
bne- livepatch_handler
--
2.12.1
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