From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 6F9F43858D35; Fri, 17 Nov 2023 06:35:10 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6F9F43858D35 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1700202910; bh=3QSKEs+WuAE32+S/yQvoPzN2cW7MpNbaI8/en18u0SQ=; h=From:To:Subject:Date:From; b=ZKmwWFiYxp2hkIGlf21UEjlj0B3FeDfuZt1evi62DGWkLHPA/ykqwfQbR5vibcjJy 8ZEEWfxdS2V/I/6LWrKfuY7v7REOv39s+Y9KWRg7JkAxDGas4oj6gmdtFJuBuEBNBC cZrmQ+TzFyCFy6g6xS0M2JW1uQv98bo8d0PMvrJY= From: "iamanonymous.cs at gmail dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug debug/112582] New: Inconsistent Variable Values: Discrepancy between Source-Level and Instruction-Level Debugging Date: Fri, 17 Nov 2023 06:35:09 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: debug X-Bugzilla-Version: 14.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: iamanonymous.cs at gmail 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 Message-ID: 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: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112582 Bug ID: 112582 Summary: Inconsistent Variable Values: Discrepancy between Source-Level and Instruction-Level Debugging Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: debug Assignee: unassigned at gcc dot gnu.org Reporter: iamanonymous.cs at gmail dot com Target Milestone: --- ######################## As shows in the following, we can observed that the values of variables x a= nd y exhibit inconsistencies between source-level debugging and instruction-level debugging prior to entering the function foo. I'm not sure whether the inconsistency is a result of code optimization. ######################## ###### source-level debugging ###### $ gcc -O2 -g small.c root@ubuntu:~# gdb -q a.out Reading symbols from a.out... (gdb) b main Breakpoint 1 at 0x401060: file small.c, line 30. (gdb) r Starting program: /root/a.out=20 Breakpoint 1, main () at small.c:30 30 x =3D -5; (gdb) s 31 y =3D -10; (gdb) s 32 foo (&x, &y); (gdb) info locals x =3D 65531 y =3D 65526 (gdb)=20 ###### instruction-level debugging ###### $ gcc -O2 -g small.c; gdb -q a.out Reading symbols from a.out... (gdb) b main Breakpoint 1 at 0x401060: file small.c, line 27. (gdb) r Starting program: /root/a.out=20 Breakpoint 1, main () at small.c:27 27 x =3D -5; (gdb) si 0x0000000000401064 27 x =3D -5; (gdb) info locals x =3D 0 y =3D 0 (gdb) si 0x0000000000401069 28 y =3D -10; (gdb) info locals x =3D 0 y =3D 0 (gdb) si 0x000000000040106e 29 foo (&x, &y); (gdb) info locals x =3D 0 y =3D 0 (gdb)=20 ###### bug-triggering code ###### $ cat small.c extern void abort (void); extern void exit (int); __attribute__ ((noinline)) void foo(short unsigned int *p1, short unsigned int *p2) { short unsigned int x1, x4; int x2, x3, x5, x6; unsigned int x7; x1 =3D *p1; x2 =3D (int) x1; x3 =3D x2 * 65536; x4 =3D *p2; x5 =3D (int) x4; x6 =3D x3 + x4; x7 =3D (unsigned int) x6; if (x7 <=3D 268435455U) abort (); exit (0); } int main() { short unsigned int x, y; x =3D -5; y =3D -10; foo (&x, &y); } ###### gcc and gdb version ###### $ gcc --version gcc (GCC) 14.0.0 20231116 (experimental) Copyright (C) 2023 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. $ gdb --version GNU gdb (GDB) 15.0.50.20231116-git Copyright (C) 2023 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.=