Commit 06e24745 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

objtool: Remove annotate_{,un}reachable() 



There are no users of annotate_reachable() left.

And the annotate_unreachable() usage in unreachable() is plain wrong;
it will hide dangerous fall-through code-gen.

Remove both.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20241128094312.235637588@infradead.org
parent 624bde34

include/linux/compiler.h

+0 −27
Original line number Diff line number Diff line
@@ -109,35 +109,9 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, 


/* Unreachable code */

#ifdef CONFIG_OBJTOOL

/*

 * These macros help objtool understand GCC code flow for unreachable code.

 * The __COUNTER__ based labels are a hack to make each instance of the macros

 * unique, to convince GCC not to merge duplicate inline asm statements.

 */

#define __stringify_label(n) #n



#define __annotate_reachable(c) ({					\

	asm volatile(__stringify_label(c) ":\n\t"			\

			".pushsection .discard.reachable\n\t"		\

			".long " __stringify_label(c) "b - .\n\t"	\

			".popsection\n\t");				\

})

#define annotate_reachable() __annotate_reachable(__COUNTER__)



#define __annotate_unreachable(c) ({					\

	asm volatile(__stringify_label(c) ":\n\t"			\

		     ".pushsection .discard.unreachable\n\t"		\

		     ".long " __stringify_label(c) "b - .\n\t"		\

		     ".popsection\n\t" : : "i" (c));			\

})

#define annotate_unreachable() __annotate_unreachable(__COUNTER__)



/* Annotate a C jump table to allow objtool to follow the code flow */

#define __annotate_jump_table __section(".rodata..c_jump_table,\"a\",@progbits #")



#else /* !CONFIG_OBJTOOL */

#define annotate_reachable()

#define annotate_unreachable()

#define __annotate_jump_table

#endif /* CONFIG_OBJTOOL */
@@ -147,7 +121,6 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, 
 * control elsewhere.

 */

#define unreachable() do {		\

	annotate_unreachable();		\

	barrier_before_unreachable();	\

	__builtin_unreachable();	\

} while (0)

tools/objtool/check.c

+2 −41
Original line number Diff line number Diff line
@@ -638,47 +638,8 @@ static int add_dead_ends(struct objtool_file *file) 
	uint64_t offset;



	/*

	 * Check for manually annotated dead ends.

	 */

	rsec = find_section_by_name(file->elf, ".rela.discard.unreachable");

	if (!rsec)

		goto reachable;



	for_each_reloc(rsec, reloc) {

		if (reloc->sym->type == STT_SECTION) {

			offset = reloc_addend(reloc);

		} else if (reloc->sym->local_label) {

			offset = reloc->sym->offset;

		} else {

			WARN("unexpected relocation symbol type in %s", rsec->name);

			return -1;

		}



		insn = find_insn(file, reloc->sym->sec, offset);

		if (insn)

			insn = prev_insn_same_sec(file, insn);

		else if (offset == reloc->sym->sec->sh.sh_size) {

			insn = find_last_insn(file, reloc->sym->sec);

			if (!insn) {

				WARN("can't find unreachable insn at %s+0x%" PRIx64,

				     reloc->sym->sec->name, offset);

				return -1;

			}

		} else {

			WARN("can't find unreachable insn at %s+0x%" PRIx64,

			     reloc->sym->sec->name, offset);

			return -1;

		}



		insn->dead_end = true;

	}



reachable:

	/*

	 * These manually annotated reachable checks are needed for GCC 4.4,

	 * where the Linux unreachable() macro isn't supported.  In that case

	 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's

	 * not a dead end.

	 * UD2 defaults to being a dead-end, allow them to be annotated for

	 * non-fatal, eg WARN.

	 */

	rsec = find_section_by_name(file->elf, ".rela.discard.reachable");

	if (!rsec)