Commit 7acfe531 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Borislav Petkov
Browse files

objtool: Improve call destination function detection 



A recent clang change, combined with a binutils bug, can trigger a
situation where a ".Lprintk$local" STT_NOTYPE symbol gets created at the
same offset as the "printk" STT_FUNC symbol.  This confuses objtool:

  kernel/printk/printk.o: warning: objtool: ignore_loglevel_setup()+0x10: can't find call dest symbol at .text+0xc67

Improve the call destination detection by looking specifically for an
STT_FUNC symbol.

Reported-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Tested-by: default avatarNathan Chancellor <natechancellor@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/872
Link: https://sourceware.org/bugzilla/show_bug.cgi?id=25551
Link: https://lkml.kernel.org/r/0a7ee320bc0ea4469bd3dc450a7b4725669e0ea9.1581997059.git.jpoimboe@redhat.com
parent 113d4bc9

tools/objtool/check.c

+18 −9
Original line number Diff line number Diff line
@@ -420,8 +420,8 @@ static void add_ignores(struct objtool_file *file) 
			break;



		case STT_SECTION:

			func = find_symbol_by_offset(rela->sym->sec, rela->addend);

			if (!func || func->type != STT_FUNC)

			func = find_func_by_offset(rela->sym->sec, rela->addend);

			if (!func)

				continue;

			break;
@@ -665,10 +665,14 @@ static int add_call_destinations(struct objtool_file *file) 
					       insn->len);

		if (!rela) {

			dest_off = insn->offset + insn->len + insn->immediate;

			insn->call_dest = find_symbol_by_offset(insn->sec,

								dest_off);

			insn->call_dest = find_func_by_offset(insn->sec, dest_off);

			if (!insn->call_dest)

				insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);



			if (insn->ignore)

				continue;



			if (!insn->call_dest && !insn->ignore) {

			if (!insn->call_dest) {

				WARN_FUNC("unsupported intra-function call",

					  insn->sec, insn->offset);

				if (retpoline)
@@ -676,11 +680,16 @@ static int add_call_destinations(struct objtool_file *file) 
				return -1;

			}



			if (insn->func && insn->call_dest->type != STT_FUNC) {

				WARN_FUNC("unsupported call to non-function",

					  insn->sec, insn->offset);

				return -1;

			}



		} else if (rela->sym->type == STT_SECTION) {

			insn->call_dest = find_symbol_by_offset(rela->sym->sec,

			insn->call_dest = find_func_by_offset(rela->sym->sec,

							      rela->addend+4);

			if (!insn->call_dest ||

			    insn->call_dest->type != STT_FUNC) {

			if (!insn->call_dest) {

				WARN_FUNC("can't find call dest symbol at %s+0x%x",

					  insn->sec, insn->offset,

					  rela->sym->sec->name,

tools/objtool/elf.c

+12 −2
Original line number Diff line number Diff line
@@ -62,8 +62,18 @@ struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset) 
	struct symbol *sym;



	list_for_each_entry(sym, &sec->symbol_list, list)

		if (sym->type != STT_SECTION &&

		    sym->offset == offset)

		if (sym->type != STT_SECTION && sym->offset == offset)

			return sym;



	return NULL;

}



struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)

{

	struct symbol *sym;



	list_for_each_entry(sym, &sec->symbol_list, list)

		if (sym->type == STT_FUNC && sym->offset == offset)

			return sym;



	return NULL;

tools/objtool/elf.h

+1 −0
Original line number Diff line number Diff line
@@ -77,6 +77,7 @@ struct elf { 


struct elf *elf_read(const char *name, int flags);

struct section *find_section_by_name(struct elf *elf, const char *name);

struct symbol *find_func_by_offset(struct section *sec, unsigned long offset);

struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);

struct symbol *find_symbol_by_name(struct elf *elf, const char *name);

struct symbol *find_symbol_containing(struct section *sec, unsigned long offset);

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