From 9d636109511a000882f8dff4eaafa874eec5ece8 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Tue, 19 Jul 2016 14:48:30 +1000 Subject: [PATCH] powerpc/ftrace: Separate the heuristics for checking call sites 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 --- 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..cc52d9795f88 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 mflr 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"); -- 2.20.1