This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH] Improve dead code elimination with -fsanitize=address (PR84307)
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Paolo Bonzini <bonzini at gnu dot org>, Marek Polacek <polacek at redhat dot com>
- Cc: gcc-patches at gcc dot gnu dot org, marcandre dot lureau at redhat dot com, mliska at suse dot cz
- Date: Tue, 13 Feb 2018 15:40:20 +0100
- Subject: Re: [PATCH] Improve dead code elimination with -fsanitize=address (PR84307)
- Authentication-results: sourceware.org; auth=none
- References: <1518192504-49084-1-git-send-email-bonzini@gnu.org>
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Fri, Feb 09, 2018 at 05:08:24PM +0100, Paolo Bonzini wrote:
> PR sanitizer/84307
> * gcc.dg/asan/pr84307.c: New test.
BTW, your testcase shows a more severe problem, that we actually don't
handle compound literals correctly.
C99 says that:
"If the compound literal occurs outside the body of a function, the object
has static storage duration; otherwise, it has automatic storage duration
associated with the enclosing block."
but if we create an object with automatic storage duration, we don't
actually put that object into the scope of the enclosing block, but of the
enclosing function, which explains the weird ASAN_MARK UNPOISON present, but
corresponding ASAN_MARK POISON not present. The following testcase should
IMHO FAIL with -fsanitize=address on the second bar call, but doesn't, even
at -O0 without any DSE. When optimizing we because of this don't emit
CLOBBER stmts when the compound literal object goes out of scope, and with
-fsanitize=address -fsanitize-address-use-after-scope we don't emit the
POISON.
struct S { int s; } *p;
static inline void
foo (struct S *x)
{
p = x;
}
static inline void
bar (void)
{
p->s = 5;
}
int
main ()
{
{
foo (&(struct S) { 1 });
bar ();
}
{
foo (&(struct S) { 2 });
}
bar ();
return 0;
}
The following untested patch seems to cure thatm will see how much it will
break.
2018-02-13 Jakub Jelinek <jakub@redhat.com>
PR sanitizer/84340
* c-decl.c (build_compound_literal): Call pushdecl (decl) even when
it is not TREE_STATIC.
--- gcc/c/c-decl.c.jj 2018-01-03 10:20:20.114537949 +0100
+++ gcc/c/c-decl.c 2018-02-13 15:17:47.091186077 +0100
@@ -5348,6 +5348,8 @@ build_compound_literal (location_t loc,
pushdecl (decl);
rest_of_decl_compilation (decl, 1, 0);
}
+ else
+ pushdecl (decl);
if (non_const)
{
Jakub