https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93910
Bug ID: 93910
Summary: -Waddress-of-packed-member triggered without actual
access to a member or the address of a member
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: stephane.goujet at wanadoo dot fr
Target Milestone: ---
Hello,
This warning is triggered when I just cast the address of a packed structure
to an int pointer. I am not trying to access (the address of) one of its
members, which should be the sole purpose of this warning as I understand it.
Here is the *.i from my test file, with a simplistic struct:
----------------------
# 1 "test2.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 31 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 32 "<command-line>" 2
# 1 "test2.c"
struct __attribute__ ((__packed__)) S {
int a;
};
int main(void) {
struct S s;
char *pc = (char *) &s;
int *pi = (int *) &s;
return 0;
}
---------------------
and the compilation command and result:
---------------------
~/test/c/gcc9packed $LC_ALL=C gcc -Wextra test2.c -save-temps
test2.c: In function 'main':
test2.c:9:5: warning: converting a packed 'struct S' pointer (alignment 1) to a
'int' pointer (alignment 4) may result in an unaligned pointer value
[-Waddress-of-packed-member]
9 | int *pi = (int *) &s;
| ^~~
test2.c:2:37: note: defined here
2 | struct __attribute__ ((__packed__)) S {
|
---------------------
GCC version is 9.2.0:
---------------------
~/test/c/gcc9packed $LC_ALL=C gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-pc-linux-gnu/9.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-9.2.0/configure --enable-gold=yes
--enable-languages=d,fortran,objc : (reconfigured) ../gcc-9.2.0/configure
--enable-gold=yes --enable-languages=d
Thread model: posix
gcc version 9.2.0 (GCC)
---------------------
As a (not so important) side note, there are spelling mistakes in the French
version of the warning message. One occurrence of 'pointer' is translated (to
'pointeur'), the other two remained in English:
---------------------
test2.c: Dans la fonction « main »:
test2.c:9:5: attention: convertir un pointer « struct S » compacté (alignement
1) vers un pointeur « int » (alignement 4) peut résulter en une valeur de
pointer non alignée [-Waddress-of-packed-member]
9 | int *pi = (int *) &s;
| ^~~
test2.c:2:37: note: défini ici
2 | struct __attribute__ ((__packed__)) S {
|
----------------------
