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objtool, kcsan: Remove memory barrier instrumentation from noinstr

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Teach objtool to turn instrumentation required for memory barrier
modeling into nops in noinstr text.

The __tsan_func_entry/exit calls are still emitted by compilers even
with the __no_sanitize_thread attribute. The memory barrier
instrumentation will be inserted explicitly (without compiler help), and
thus needs to also explicitly be removed.

Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Marco Elver 2021-11-30 12:44:31 +01:00 committed by Paul E. McKenney
parent 0525bd82f6
commit 0509811952
2 changed files with 32 additions and 7 deletions
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37
tools/objtool/check.c
View file

@ -1072,11 +1072,11 @@ static void annotate_call_site(struct objtool_file *file,
}
/*
* Many compilers cannot disable KCOV with a function attribute
* so they need a little help, NOP out any KCOV calls from noinstr
* text.
* Many compilers cannot disable KCOV or sanitizer calls with a function
* attribute so they need a little help, NOP out any such calls from
* noinstr text.
*/
if (insn->sec->noinstr && sym->kcov) {
if (insn->sec->noinstr && sym->profiling_func) {
if (reloc) {
reloc->type = R_NONE;
elf_write_reloc(file->elf, reloc);
@ -1991,6 +1991,31 @@ static int read_intra_function_calls(struct objtool_file *file)
return 0;
}
/*
* Return true if name matches an instrumentation function, where calls to that
* function from noinstr code can safely be removed, but compilers won't do so.
*/
static bool is_profiling_func(const char *name)
{
/*
* Many compilers cannot disable KCOV with a function attribute.
*/
if (!strncmp(name, "__sanitizer_cov_", 16))
return true;
/*
* Some compilers currently do not remove __tsan_func_entry/exit nor
* __tsan_atomic_signal_fence (used for barrier instrumentation) with
* the __no_sanitize_thread attribute, remove them. Once the kernel's
* minimum Clang version is 14.0, this can be removed.
*/
if (!strncmp(name, "__tsan_func_", 12) ||
!strcmp(name, "__tsan_atomic_signal_fence"))
return true;
return false;
}
static int classify_symbols(struct objtool_file *file)
{
struct section *sec;
@ -2011,8 +2036,8 @@ static int classify_symbols(struct objtool_file *file)
if (!strcmp(func->name, "__fentry__"))
func->fentry = true;
if (!strncmp(func->name, "__sanitizer_cov_", 16))
func->kcov = true;
if (is_profiling_func(func->name))
func->profiling_func = true;
}
}

2
tools/objtool/include/objtool/elf.h
View file

@ -58,7 +58,7 @@ struct symbol {
u8 static_call_tramp : 1;
u8 retpoline_thunk : 1;
u8 fentry : 1;
u8 kcov : 1;
u8 profiling_func : 1;
struct list_head pv_target;
};