[llvm-bugs] [Bug 35941] New: Missing -Waddress-of-packed-member check

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35941

            Bug ID: 35941
           Summary: Missing -Waddress-of-packed-member check
           Product: new-bugs
           Version: 4.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: hjl.tools at gmail.com
                CC: llvm-bugs at lists.llvm.org

[hjl at gnu-tools-1 pr51628]$ cat p.c
#include <stdio.h>
#include <stddef.h>
int main(void)
{
    struct foo {
        char c;
        int x;
    } __attribute__((packed));
    struct foo arr[2] = { { 'a', 10 }, {'b', 20 } };
    int *p0 = &arr[0].x;
    int *p1 = &arr[1].x;
    printf("sizeof(struct foo) = %d\n",
           (int)sizeof(struct foo));
    printf("offsetof(struct foo, c) = %d\n",
           (int)offsetof(struct foo, c));
    printf("offsetof(struct foo, x) = %d\n",
           (int)offsetof(struct foo, x));
    printf("arr[0].x = %d\n", arr[0].x);
    printf("arr[1].x = %d\n", arr[1].x);
    printf("p0 = %p\n", (void*)p0);
    printf("p1 = %p\n", (void*)p1);
    printf("*p0 = %d\n", *p0);
    printf("*p1 = %d\n", *p1);
    return 0;
}
[hjl at gnu-tools-1 pr51628]$ clang -S p.c
[hjl at gnu-tools-1 pr51628]$
/export/build/gnu/gcc-test/build-x86_64-linux/gcc/xg++
-B/export/build/gnu/gcc-test/build-x86_64-linux/gcc/ -O2 -S p.c
p.c: In function ‘int main()’:
p.c:10:23: warning: initialization of ‘int*’ from address of member of packed
‘main()::foo’ may result in an unaligned pointer value
[-Waddress-of-packed-member]
     int *p0 = &arr[0].x;
                       ^
p.c:11:23: warning: initialization of ‘int*’ from address of member of packed
‘main()::foo’ may result in an unaligned pointer value
[-Waddress-of-packed-member]
     int *p1 = &arr[1].x;
                       ^
[hjl at gnu-tools-1 pr51628]$

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