https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112543
Bug ID: 112543
Summary: warning pointer used after free() for printf("%p")
Product: gcc
Version: 13.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: mario at klebsch dot de
Target Milestone: ---
Created attachment 56592
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56592&action=edit
main.c preprocessed by gcc
Hello,
Compiling the following program with -Wall gives a use-after-free warning:
----8<--------8<--------8<--------8<--------8<--------8<----
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
char* p = (char*)malloc(5);
printf("allocated %p\n", p);
free(p);
printf("freed %p\n", p);
}
----8<--------8<--------8<--------8<--------8<--------8<----
Compiling with gcc gives this output:
mkl@C707 ~/tmp/g++-bug $ gcc -Wall main.c -o main
main.c: In function ‘main’:
main.c:9:9: warning: pointer ‘p’ used after ‘free’ [-Wuse-after-free]
9 | printf("freed %p\n", p);
| ^~~~~~~~~~~~~~~~~~~~~~~
main.c:8:9: note: call to ‘free’ here
8 | free(p);
| ^~~~~~~
mkl@C707 ~/tmp/g++-bug $ gcc --version
gcc (Gentoo 13.2.1_p20230826 p7) 13.2.1 20230826
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.
mkl@C707 ~/tmp/g++-bug $
Compiling with g++:
mkl@C707 ~/tmp/g++-bug $ g++ -Wall main.cpp -o main
main.cpp: In function ‘int main(int, char**)’:
main.cpp:9:15: warning: pointer ‘p’ used after ‘void free(void*)’
[-Wuse-after-free]
9 | printf("freed %p\n", p);
| ~~~~~~^~~~~~~~~~~~~~~~~
main.cpp:8:13: note: call to ‘void free(void*)’ here
8 | free(p);
| ~~~~^~~
mkl@C707 ~/tmp/g++-bug $ g++ --version
g++ (Gentoo 13.2.1_p20230826 p7) 13.2.1 20230826
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.
mkl@C707 ~/tmp/g++-bug $
