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* [Bug c/68046] New: -ftrapv doesn't catch leaq-based overflows on x86-64
@ 2015-10-21 22:39 eggert at gnu dot org
2015-10-21 22:48 ` [Bug middle-end/68046] " pinskia at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: eggert at gnu dot org @ 2015-10-21 22:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68046
Bug ID: 68046
Summary: -ftrapv doesn't catch leaq-based overflows on x86-64
Product: gcc
Version: 5.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: eggert at gnu dot org
Target Milestone: ---
On x86-64 for this program:
long i = 0x7fffffffffffffffL;
int main (void)
{
return i + 1 < i;
}
gcc -ftrapv -O2 -S generates this code:
main:
movq i(%rip), %rax
leaq 1(%rax), %rdx
cmpq %rdx, %rax
setg %al
movzbl %al, %eax
ret
which does not trap, even though the addition overflows.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/68046] -ftrapv doesn't catch leaq-based overflows on x86-64
2015-10-21 22:39 [Bug c/68046] New: -ftrapv doesn't catch leaq-based overflows on x86-64 eggert at gnu dot org
@ 2015-10-21 22:48 ` pinskia at gcc dot gnu.org
2015-10-21 23:46 ` joseph at codesourcery dot com
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2015-10-21 22:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68046
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|c |middle-end
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
-fsantize=undefined is more recommended for Linux and recent versions of gcc
instead of -ftrapv.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/68046] -ftrapv doesn't catch leaq-based overflows on x86-64
2015-10-21 22:39 [Bug c/68046] New: -ftrapv doesn't catch leaq-based overflows on x86-64 eggert at gnu dot org
2015-10-21 22:48 ` [Bug middle-end/68046] " pinskia at gcc dot gnu.org
@ 2015-10-21 23:46 ` joseph at codesourcery dot com
2015-10-22 8:19 ` rguenth at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: joseph at codesourcery dot com @ 2015-10-21 23:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68046
--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
I wonder if it would be possible to map -ftrapv to something like
-fsanitize=signed-integer-overflow -fsanitize-undefined-trap-on-error
(whatever is most closely equivalent to -ftrapv and doesn't require
libubsan). Then we could get rid of the separate -ftrapv code paths,
which never worked well (while keeping the shared libgcc functions for
compatibility, of course).
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/68046] -ftrapv doesn't catch leaq-based overflows on x86-64
2015-10-21 22:39 [Bug c/68046] New: -ftrapv doesn't catch leaq-based overflows on x86-64 eggert at gnu dot org
2015-10-21 22:48 ` [Bug middle-end/68046] " pinskia at gcc dot gnu.org
2015-10-21 23:46 ` joseph at codesourcery dot com
@ 2015-10-22 8:19 ` rguenth at gcc dot gnu.org
2015-10-22 8:47 ` rguenth at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2015-10-22 8:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68046
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |DUPLICATE
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
If we have a variant that doesn't require libubsan (which is not available
on all targets) then yes, that would indeed be nice. Of course it's restricted
to the C family languages while -ftrapv was "working" for all languages before
(though IIRC Ada has its own implementation).
Note this bug may be a duplicate (and I must admit I didn't end up committing
a few fixes I had for some of the -ftrapv bugs...). The testcase works in
my dev tree:
main:
.LFB0:
.cfi_startproc
pushq %rbx
.cfi_def_cfa_offset 16
.cfi_offset 3, -16
movq i(%rip), %rbx
movl $1, %esi
movq %rbx, %rdi
call __addvdi3
cmpq %rax, %rbx
setg %al
movzbl %al, %eax
popq %rbx
.cfi_def_cfa_offset 8
ret
> ./a.out
Aborted
Sorry about that... :/ (see PR61893)
I'm going to re-test and commit the optab changes (which I believe triggers
the above issue).
*** This bug has been marked as a duplicate of bug 61893 ***
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/68046] -ftrapv doesn't catch leaq-based overflows on x86-64
2015-10-21 22:39 [Bug c/68046] New: -ftrapv doesn't catch leaq-based overflows on x86-64 eggert at gnu dot org
` (2 preceding siblings ...)
2015-10-22 8:19 ` rguenth at gcc dot gnu.org
@ 2015-10-22 8:47 ` rguenth at gcc dot gnu.org
2015-10-22 11:44 ` rguenth at gcc dot gnu.org
2015-10-23 8:57 ` ebotcazou at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2015-10-22 8:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68046
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note that -fsanitize-undefined doesn't properly handle
volatile int x = __INT_MAX__ + 1;
which is in PR61893, it handles the case in this PR fine and with
trap-on-error more efficiently than -ftrapv:
main:
.LFB0:
.cfi_startproc
movq i(%rip), %rax
movq %rax, %rdx
addq $1, %rdx
jo .L6
cmpq %rdx, %rax
setg %al
movzbl %al, %eax
ret
.L6:
ud2
.cfi_endproc
of course you simply get a SIGILL (on x86_64), an option to use
abort () would be more "compatible" with how -ftrapv behaves
(abort is also used on targets that do not have a trapping instruction
defined).
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/68046] -ftrapv doesn't catch leaq-based overflows on x86-64
2015-10-21 22:39 [Bug c/68046] New: -ftrapv doesn't catch leaq-based overflows on x86-64 eggert at gnu dot org
` (3 preceding siblings ...)
2015-10-22 8:47 ` rguenth at gcc dot gnu.org
@ 2015-10-22 11:44 ` rguenth at gcc dot gnu.org
2015-10-23 8:57 ` ebotcazou at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2015-10-22 11:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68046
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Thu Oct 22 11:44:11 2015
New Revision: 229170
URL: https://gcc.gnu.org/viewcvs?rev=229170&root=gcc&view=rev
Log:
2015-10-22 Richard Biener <rguenther@suse.de>
PR middle-end/68046
PR middle-end/61893
* optabs.c (emit_libcall_block_1): Allow a NULL_RTX equiv.
(expand_binop): For -ftrapv optabs do not record an REG_EQUAL note.
(expand_unop): Likewise.
* gcc.dg/torture/ftrapv-2.c: New testcase.
Added:
trunk/gcc/testsuite/gcc.dg/torture/ftrapv-2.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/optabs.c
trunk/gcc/testsuite/ChangeLog
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/68046] -ftrapv doesn't catch leaq-based overflows on x86-64
2015-10-21 22:39 [Bug c/68046] New: -ftrapv doesn't catch leaq-based overflows on x86-64 eggert at gnu dot org
` (4 preceding siblings ...)
2015-10-22 11:44 ` rguenth at gcc dot gnu.org
@ 2015-10-23 8:57 ` ebotcazou at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: ebotcazou at gcc dot gnu.org @ 2015-10-23 8:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68046
Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ebotcazou at gcc dot gnu.org
--- Comment #6 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> If we have a variant that doesn't require libubsan (which is not available
> on all targets) then yes, that would indeed be nice. Of course it's
> restricted to the C family languages while -ftrapv was "working" for all
> languages before (though IIRC Ada has its own implementation).
Correct, the Ada compiler doesn't use -ftrapv at all, it's too broad.
^ permalink raw reply [flat|nested] 7+ messages in thread
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2015-10-21 22:39 [Bug c/68046] New: -ftrapv doesn't catch leaq-based overflows on x86-64 eggert at gnu dot org
2015-10-21 22:48 ` [Bug middle-end/68046] " pinskia at gcc dot gnu.org
2015-10-21 23:46 ` joseph at codesourcery dot com
2015-10-22 8:19 ` rguenth at gcc dot gnu.org
2015-10-22 8:47 ` rguenth at gcc dot gnu.org
2015-10-22 11:44 ` rguenth at gcc dot gnu.org
2015-10-23 8:57 ` ebotcazou at gcc dot gnu.org
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