objtool: Fix seg fault with Clang non-section symbols

The Clang assembler likes to strip section symbols, which means objtool
can't reference some text code by its section.  This confuses objtool
greatly, causing it to seg fault.

The fix is similar to what was done before, for ORC reloc generation:

  e81e07244325 ("objtool: Support Clang non-section symbols in ORC generation")

Factor out that code into a common helper and use it for static call
reloc generation as well.

Reported-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://github.com/ClangBuiltLinux/linux/issues/1207
Link: https://lkml.kernel.org/r/ba6b6c0f0dd5acbba66e403955a967d9fdd1726a.1607983452.git.jpoimboe@redhat.com

1 files changed, 26 insertions, 0 deletions

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 4e1d7460574b..be89c741ba9a 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -262,6 +262,32 @@ struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, uns
 	return find_reloc_by_dest_range(elf, sec, offset, 1);
 }
 
+void insn_to_reloc_sym_addend(struct section *sec, unsigned long offset,
+			      struct reloc *reloc)
+{
+	if (sec->sym) {
+		reloc->sym = sec->sym;
+		reloc->addend = offset;
+		return;
+	}
+
+	/*
+	 * The Clang assembler strips section symbols, so we have to reference
+	 * the function symbol instead:
+	 */
+	reloc->sym = find_symbol_containing(sec, offset);
+	if (!reloc->sym) {
+		/*
+		 * Hack alert.  This happens when we need to reference the NOP
+		 * pad insn immediately after the function.
+		 */
+		reloc->sym = find_symbol_containing(sec, offset - 1);
+	}
+
+	if (reloc->sym)
+		reloc->addend = offset - reloc->sym->offset;
+}
+
 static int read_sections(struct elf *elf)
 {
 	Elf_Scn *s = NULL;