https://bugs.kde.org/show_bug.cgi?id=500979
Bug ID: 500979
Summary: botch of 'notrack' prefix for i386
Classification: Developer tools
Product: valgrind
Version: 3.24.0
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: memcheck
Assignee: jsew...@acm.org
Reporter: jrei...@bitwagon.com
Target Milestone: ---
SUMMARY
Memcheck emulates incorrectly the 'notrack' instruction prefix of i386 code
when run on amd64.
STEPS TO REPRODUCE
0. $ cat notrack.S # the i386 assembly code
_start: .globl _start
push $0 # keep stack 2-word aligned after 'call'
call jmp_back
hlt
jmp_back:
push %esp
pop %ebp
.byte 0x3e; jmp *(%ebp)
1. gcc -m32 -g -nostartfiles -nostdlib -o notrack notrack.S # compile and
build for i386 on amd64
2. valgrind ./notrack # run on amd64 with Linux support for executing i386
programs
3. gdb notrack # detailed examination of code; see below
OBSERVED RESULT
$ valgrind ./notrack
==748797== Memcheck, a memory error detector
==748797== Copyright (C) 2002-2024, and GNU GPL'd, by Julian Seward et al.
==748797== Using Valgrind-3.24.0 and LibVEX; rerun with -h for copyright info
==748797== Command: ./notrack
==748797==
==748797==
==748797== Process terminating with default action of signal 11 (SIGSEGV):
dumping core
==748797== General Protection Fault
==748797== at 0x804900A: ??? (notrack.S:8)
==748797==
$ gdb ./notrack # step-by-step run without valgrind (memcheck)
(gdb) b jmp_back
Breakpoint 1 at 0x8049008: file notrack.S, line 7.
(gdb) run
Starting program: ./notrack
Breakpoint 1, jmp_back () at notrack.S:7
7 push %esp
(gdb) x/i $pc
=> 0x8049008 <jmp_back>: push %esp
(gdb) p $esp
$1 = (void *) 0xffffcc78
(gdb) stepi
8 pop %ebp
=> 0x8049009 <jmp_back+1>: pop %ebp
(gdb) stepi
0x0804900a in jmp_back () at notrack.S:8
8 pop %ebp
=> 0x804900a <jmp_back+2>: notrack jmp *0x0(%ebp) ## the address of
memcheck complaint
(gdb) x/xw $ebp
0xffffcc78: 0x08049007
(gdb) x/i 0x08049007
0x8049007 <_start+7>: hlt
(gdb) stepi
_start () at notrack.S:4
4 hlt ## successful return to the instruction after the 'call'
(gdb) q
EXPECTED RESULT
No complaint
SOFTWARE/OS VERSIONS
Windows:
macOS:
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: Linux 6.12.13 (Fedora 40)
KDE Plasma Version:
KDE Frameworks Version:
Qt Version:
ADDITIONAL INFORMATION
$ uname -a
Linux fedora 6.12.13-100.fc40.x86_64 #1 SMP PREEMPT_DYNAMIC Sat Feb 8 17:10:01
UTC 2025 x86_64 GNU/Linux
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