[PATCH v2 11/53] objtool/klp: Fix handling of zero-length .altinstr_replacement sections

[Josh Poimboeuf <jpoimboe@kernel.org>]

When a section is empty (e.g. only zero-length alternative
replacements), there are no symbols to convert a section symbol
reference to.  Skip the reloc instead of erroring out.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 30ce234e01a1..a226e99948b3 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1005,6 +1005,13 @@ static int convert_reloc_secsym_to_sym(struct elf *elf, struct reloc *reloc)
 	/* No dedicated section; find the symbol manually */
 	sym = find_symbol_containing(sec, arch_adjusted_addend(reloc));
 	if (!sym) {
+		/*
+		 * This is presumably an .altinstr_replacement section which is
+		 * empty due to it only having zero-length replacement(s).
+		 */
+		if (!sec_size(sec))
+			return 1;
+
 		/*
 		 * This can happen for special section references to weak code
 		 * whose symbol has been stripped by the linker.
@@ -1265,6 +1272,7 @@ static int clone_sym_relocs(struct elfs *e, struct symbol *patched_sym)
 
 	for_each_reloc(patched_rsec, patched_reloc) {
 		unsigned long offset;
+		int ret;
 
 		if (reloc_offset(patched_reloc) < start ||
 		    reloc_offset(patched_reloc) >= end)
@@ -1278,12 +1286,15 @@ static int clone_sym_relocs(struct elfs *e, struct symbol *patched_sym)
 		    !strcmp(patched_reloc->sym->sec->name, ".altinstr_aux"))
 			continue;
 
-		if (convert_reloc_sym(e->patched, patched_reloc)) {
+		ret = convert_reloc_sym(e->patched, patched_reloc);
+		if (ret < 0) {
 			ERROR_FUNC(patched_rsec->base, reloc_offset(patched_reloc),
 				   "failed to convert reloc sym '%s' to its proper format",
 				   patched_reloc->sym->name);
 			return -1;
 		}
+		if (ret > 0)
+			continue;
 
 		offset = out_sym->offset + (reloc_offset(patched_reloc) - patched_sym->offset);
 
-- 
2.53.0