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Commit 9d636109 authored by Michael Ellerman's avatar Michael Ellerman
Browse files

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: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent b1923caa

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");