powerpc/ftrace: Separate the heuristics for checking call sites (9d636109) · Commits · 戴 / test

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@ellerman.id.au>

arch/powerpc/kernel/ftrace.c

+18 −17

Original line number	Diff line number	Diff line
		@@ -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);
		pr_err("Expected %08x found %08x\n", PPC_INST_LD_TOC, op);
		return -EINVAL;
		}

		/* When using -mkernel_profile there is no load to jump over */
		pop = PPC_INST_NOP;
		}
		#endif /* CC_USING_MPROFILE_KERNEL */

		if (patch_instruction((unsigned int *)ip, pop)) {
		pr_err("Patching NOP failed.\n");

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