objtool: Generate ORC data for __pfx code

Allow unwinding from prefix code by copying the CFI from the starting
instruction of the corresponding function.  Even when the NOPs are
replaced, they're still stack-invariant instructions so the same ORC
entry can be reused everywhere.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/bc3344e51f3e87102f1301a0be0f72a7689ea4a4.1681331135.git.jpoimboe@kernel.org

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8ee4d51de6fa87e912980c4d5cd4674e9d515944..df634dafefc4ed5dbcd70f5ab98e83538db9c694 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4117,6 +4117,7 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
 static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
 {
        struct instruction *insn, *prev;
+       struct cfi_state *cfi;
 
        insn = find_insn(file, func->sec, func->offset);
        if (!insn)
@@ -4145,6 +4146,19 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
        if (!prev)
                return -1;
 
+       if (!insn->cfi) {
+               /*
+                * This can happen if stack validation isn't enabled or the
+                * function is annotated with STACK_FRAME_NON_STANDARD.
+                */
+               return 0;
+       }
+
+       /* Propagate insn->cfi to the prefix code */
+       cfi = cfi_hash_find_or_add(insn->cfi);
+       for (; prev != insn; prev = next_insn_same_sec(file, prev))
+               prev->cfi = cfi;
+
        return 0;
 }