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powerpc/ftrace: Restore LR from pt_regs 

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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Naveen N. Rao 2017-04-19 18:22:24 +05:30 committed by Michael Ellerman
parent 22d8b3dec2
commit 2f59be5b97
1 changed files with 7 additions and 6 deletions
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13
arch/powerpc/kernel/entry_64.S
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@ -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