https://bugs.kde.org/show_bug.cgi?id=453065
Bug ID: 453065
Summary: memcheck warnings when using C++
Product: valgrind
Version: 3.19.0
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: memcheck
Assignee: jsew...@acm.org
Reporter: leonardopsan...@gmail.com
Target Milestone: ---
A very simple application produces a non-clean valgrind memcheck report for no
obvious reason:
`main.cpp`
```
#include <cstdio>
struct s {};
int main (void) {
struct s value = s();
const unsigned char* obj_bytes = (const unsigned char*) &value;
size_t count = sizeof(value);
printf("[%d %s] count : %ld, obj_bytes : %p\n", __LINE__, __FUNCTION__,
count, obj_bytes);
for (size_t i = 0; i < count; i++) {
printf("%ld: %02x", i, obj_bytes[i]);
}
printf("\n");
return 0;
}
```
Compiled with:
```sh
g++ -O0 -g -std=c++11 -Wall -o main main.cpp
```
Generates a very lengthy report and I don't understand why:
```
VALGRIND_LIB=~/work/googletest/bug/valgrind/src/valgrind-3.19.0/.in_place
~/work/googletest/bug/valgrind/src/valgrind-3.19.0/coregrind/valgrind
--track-origins=yes --show-reachable=yes --leak-check=full ./main
==2544006== Memcheck, a memory error detector
==2544006== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==2544006== Using Valgrind-3.19.0 and LibVEX; rerun with -h for copyright info
==2544006== Command: ./main
==2544006==
[12 main] count : 1, obj_bytes : 0x1ffefffbaf
==2544006== Use of uninitialised value of size 8
==2544006== at 0x48C410A: _itoa_word (_itoa.c:180)
==2544006== by 0x48DF964: __vfprintf_internal (vfprintf-internal.c:1646)
==2544006== by 0x48CA58E: printf (printf.c:33)
==2544006== by 0x10921A: main (main.cpp:14)
==2544006== Uninitialised value was created by a stack allocation
==2544006== at 0x109189: main (main.cpp:5)
==2544006==
==2544006== Conditional jump or move depends on uninitialised value(s)
==2544006== at 0x48C411C: _itoa_word (_itoa.c:180)
==2544006== by 0x48DF964: __vfprintf_internal (vfprintf-internal.c:1646)
==2544006== by 0x48CA58E: printf (printf.c:33)
==2544006== by 0x10921A: main (main.cpp:14)
==2544006== Uninitialised value was created by a stack allocation
==2544006== at 0x109189: main (main.cpp:5)
==2544006==
==2544006== Conditional jump or move depends on uninitialised value(s)
==2544006== at 0x48E05E3: __vfprintf_internal (vfprintf-internal.c:1646)
==2544006== by 0x48CA58E: printf (printf.c:33)
==2544006== by 0x10921A: main (main.cpp:14)
==2544006== Uninitialised value was created by a stack allocation
==2544006== at 0x109189: main (main.cpp:5)
==2544006==
==2544006== Conditional jump or move depends on uninitialised value(s)
==2544006== at 0x48DFA87: __vfprintf_internal (vfprintf-internal.c:1646)
==2544006== by 0x48CA58E: printf (printf.c:33)
==2544006== by 0x10921A: main (main.cpp:14)
==2544006== Uninitialised value was created by a stack allocation
==2544006== at 0x109189: main (main.cpp:5)
==2544006==
0: 00
==2544006==
==2544006== HEAP SUMMARY:
==2544006== in use at exit: 0 bytes in 0 blocks
==2544006== total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==2544006==
==2544006== All heap blocks were freed -- no leaks are possible
==2544006==
==2544006== For lists of detected and suppressed errors, rerun with: -s
==2544006== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 0 from 0)
```
I first caught this issue when using Google Test:
https://github.com/google/googletest/issues/3805
The C version of pretty much the same code works file:
`main.c`
```
#include <stdio.h>
struct s {};
int main (void) {
struct s value;
const unsigned char* obj_bytes = (const unsigned char*) &value;
size_t count = sizeof(value);
printf("[%d %s] count : %ld, obj_bytes : %p\n", __LINE__, __FUNCTION__,
count, obj_bytes);
for (size_t i = 0; i < count; i++) {
printf("%ld: %02x", i, obj_bytes[i]);
}
printf("\n");
return 0;
}
```
```sh
$ gcc -O0 -g -Wall -o main main.c
```
```
$ VALGRIND_LIB=~/work/googletest/bug/valgrind/src/valgrind-3.19.0/.in_place
~/work/googletest/bug/valgrind/src/valgrind-3.19.0/coregrind/valgrind
--track-origins=yes --show-reachable=yes --leak-check=full ./main
==2544226== Memcheck, a memory error detector
==2544226== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==2544226== Using Valgrind-3.19.0 and LibVEX; rerun with -h for copyright info
==2544226== Command: ./main
==2544226==
[12 main] count : 0, obj_bytes : 0x1ffefffbaf
==2544226==
==2544226== HEAP SUMMARY:
==2544226== in use at exit: 0 bytes in 0 blocks
==2544226== total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==2544226==
==2544226== All heap blocks were freed -- no leaks are possible
==2544226==
==2544226== For lists of detected and suppressed errors, rerun with: -s
==2544226== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
```
STEPS TO REPRODUCE
1. Compile the code example above
2. Run valgrind on the binary
OBSERVED RESULT
Bunch of warnings
EXPECTED RESULT
No warnings
SOFTWARE/OS VERSIONS
valgrind-3.17.0
Operating System: Kubuntu 21.10
KDE Plasma Version: 5.22.5
KDE Frameworks Version: 5.86.0
Qt Version: 5.15.2
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