From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id D7B6D3858C3A; Thu,  1 Feb 2024 09:35:04 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org D7B6D3858C3A
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1706780104;
	bh=XGa6o0KWfO7NLOnUGkLIILQmvObvbEtUbb2OURVDwSs=;
	h=From:To:Subject:Date:From;
	b=WEPERYo0WWxaoJTHVIscR1uOpLsBx6ZJemZabIqmtVBOCQnz/l8MbgKlkzeahxqP1
	 OGwuUymafgFYMe2cVhvuQIV/k5Sw6BPuuA2p2S6vPLnFD3Iw9E4yog9Tx6qfIeXB3c
	 lIV6uDFln5kMz4dshTbCxrgdiXduG4gidZt2bYR8=
From: "jiajing_zheng at 163 dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/113702] New: -fsanitize=undefined missed a check under GCC
 12.2.0 compared to 13.2.0
Date: Thu, 01 Feb 2024 09:35:03 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 12.2.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jiajing_zheng at 163 dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
 attachments.created
Message-ID: <bug-113702-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113702

            Bug ID: 113702
           Summary: -fsanitize=3Dundefined missed a check under GCC 12.2.0
                    compared to 13.2.0
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jiajing_zheng at 163 dot com
  Target Milestone: ---

Created attachment 57278
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D57278&action=3Dedit
source C file causing the problem

I'm sorry, but I'm not sure which component causes this problem.

The sub expression '(int)(g_B * g_A[1])' in source.c has a signed overflow
problem. I checked the file using 'gcc source.c -fsanitize=3Dundefined
<optimization level> && ./a.out' at the -O0,-O1,-O2,-O3,-Os optimization le=
vels
under GCC12.2.0 and GCC13.2.0. The results showed that 'signed integer
overflow' was given under GCC13.2.0, but missed under GCC12.2.0.

I then compared the assembly parts of '(int)(g_B * g_A[1])' of the two GCC
versions at the -O0 level using 'gcc source.c -fsanitize=3Dundefined -O0 -S=
'.

Under GCC13.2.0:
.L13:
        movzbl  g_A(%rip), %r12d
        movzbl  g_A+1(%rip), %eax
        movzbl  %al, %eax
        movl    g_B(%rip), %edx
        movl    %eax, %ebx
        imull   %edx, %ebx
        jno     .L3
        movslq  %edx, %rdx
        cltq
        movq    %rax, %rsi
        movl    $.Lubsan_data3, %edi
        call    __ubsan_handle_mul_overflow

Under GCC12.2.0:
.L11:
        movzbl  g_A(%rip), %edx
        movzbl  g_A+1(%rip), %eax
        movl    g_B(%rip), %ecx
        imull   %ecx, %eax

Under GCC12.2.0, it shows that it lacks overflow judgment after 'imul'
operation. So I modified the last line 'imull   %ecx, %eax ' to the follwing
lines that I expected:
        movl  %eax, %ebx
        imull   %ecx, %eax
        jno     .L20
        movslq  %ecx, %rdx
        cltq
        movq    %rbx, %rsi
        movl    $.Lubsan_data3, %edi
        call    __ubsan_handle_mul_overflow
.L20:

Then I run 'gcc source.s -fsanitize=3Dundefined -O0 && ./a.out', and it gav=
e the
expected 'signed integer overflow' message.

I wonder why GCC12.2.0 not perform overflow judgment after imull., and what
components of 13.2.0 were modified for this issue.=