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>

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 6432d4bf08c889c128803cc5505546122118b964..b846f75d758432915dd416dc4c2906416634414e 100644 (file)
--- 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