[PATCH 1/2] powerpc/ftrace: Separate the heuristics for checking call sites
Michael Ellerman
mpe at ellerman.id.au
Tue Jul 19 14:48:30 AEST 2016
In __ftrace_make_nop() (the 64-bit version), we have code to deal with
two ftrace ABIs. There is the original ABI, which looks mostly like a
function call, and then the mprofile-kernel ABI which is just a branch.
The code tries to handle both cases, by looking for the presence of a
load to restore the TOC pointer (PPC_INST_LD_TOC). If we detect the TOC
load, we assume the call site is for an mcount() call using the old ABI.
That means we patch the mcount() call with a b +8, to branch over the
TOC load.
However if the kernel was built with mprofile-kernel, then there will
never be a call site using the original ftrace ABI. If for some reason
we do see a TOC load, then it's there for a good reason, and we should
not jump over it.
So split the code, using the existing CC_USING_MPROFILE_KERNEL. Kernels
built with mprofile-kernel will only look for, and expect, the new ABI,
and similarly for the original ABI.
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
---
arch/powerpc/kernel/ftrace.c | 35 ++++++++++++++++++-----------------
1 file changed, 18 insertions(+), 17 deletions(-)
diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 7af6c4de044b..438442dac44c 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -144,6 +144,21 @@ __ftrace_make_nop(struct module *mod,
return -EINVAL;
}
+#ifdef CC_USING_MPROFILE_KERNEL
+ /* When using -mkernel_profile there is no load to jump over */
+ pop = PPC_INST_NOP;
+
+ if (probe_kernel_read(&op, (void *)(ip - 4), 4)) {
+ pr_err("Fetching instruction at %lx failed.\n", ip - 4);
+ return -EFAULT;
+ }
+
+ /* We expect either a mlfr r0, or a std r0, LRSAVE(r1) */
+ if (op != PPC_INST_MFLR && op != PPC_INST_STD_LR) {
+ pr_err("Unexpected instruction %08x around bl _mcount\n", op);
+ return -EINVAL;
+ }
+#else
/*
* Our original call site looks like:
*
@@ -170,24 +185,10 @@ __ftrace_make_nop(struct module *mod,
}
if (op != PPC_INST_LD_TOC) {
- unsigned int inst;
-
- if (probe_kernel_read(&inst, (void *)(ip - 4), 4)) {
- pr_err("Fetching instruction at %lx failed.\n", ip - 4);
- return -EFAULT;
- }
-
- /* We expect either a mlfr r0, or a std r0, LRSAVE(r1) */
- if (inst != PPC_INST_MFLR && inst != PPC_INST_STD_LR) {
- pr_err("Unexpected instructions around bl _mcount\n"
- "when enabling dynamic ftrace!\t"
- "(%08x,bl,%08x)\n", inst, op);
- return -EINVAL;
- }
-
- /* When using -mkernel_profile there is no load to jump over */
- pop = PPC_INST_NOP;
+ pr_err("Expected %08x found %08x\n", PPC_INST_LD_TOC, op);
+ return -EINVAL;
}
+#endif /* CC_USING_MPROFILE_KERNEL */
if (patch_instruction((unsigned int *)ip, pop)) {
pr_err("Patching NOP failed.\n");
--
2.7.4
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