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objtool: Remove annotate_{,un}reachable()

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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: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20241128094312.235637588@infradead.org
This commit is contained in:
Peter Zijlstra 2024-11-28 10:39:04 +01:00
parent 624bde3465
commit 06e2474598
2 changed files with 2 additions and 68 deletions
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27
include/linux/compiler.h
View File

@ -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)

43
tools/objtool/check.c
View File

@ -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)