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Subject[tip:x86/pti] objtool: Add Clang support
Commit-ID:  3c1f05835cbf9fdfe60b81c718d82ceb94b6c55e
Gitweb: https://git.kernel.org/tip/3c1f05835cbf9fdfe60b81c718d82ceb94b6c55e
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Thu, 22 Mar 2018 13:00:37 -0500
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 27 Mar 2018 08:21:29 +0200

objtool: Add Clang support

Since the ORC unwinder was made the default on x86_64, Clang-built
defconfig kernels have triggered some new objtool warnings:

drivers/gpu/drm/i915/i915_gpu_error.o: warning: objtool: i915_error_printf()+0x6c: return with modified stack frame
drivers/gpu/drm/i915/intel_display.o: warning: objtool: pipe_config_err()+0xa6: return with modified stack frame

The problem is that objtool has never seen clang-built binaries before.

Shockingly enough, objtool is apparently able to follow the code flow
mostly fine, except for one instruction sequence. Instead of a LEAVE
instruction, clang restores RSP and RBP the long way:

67c: 48 89 ec mov %rbp,%rsp
67f: 5d pop %rbp

Teach objtool about this new code sequence.

Reported-and-test-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/fce88ce81c356eedcae7f00ed349cfaddb3363cc.1521741586.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
tools/objtool/check.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 92b6a2c21631..5409f6f6c48d 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1386,6 +1386,17 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
state->vals[op->dest.reg].offset = -state->stack_size;
}

+ else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
+ cfa->base == CFI_BP) {
+
+ /*
+ * mov %rbp, %rsp
+ *
+ * Restore the original stack pointer (Clang).
+ */
+ state->stack_size = -state->regs[CFI_BP].offset;
+ }
+
else if (op->dest.reg == cfa->base) {

/* mov %reg, %rsp */
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