Comment 11 for bug 392501

Forwarded from https://launchpad.net/bugs/392501

It seems that the actual size of "struct dirent" with LFS enabled is 280 bytes,
but when defined for 32bit applications, the defined struct ends up at 276, and
something (the kernel?) is still writing the remaining 4 bytes.

Built on 64bit:
cc -Wall -Werror -fstack-protector -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
-o test-native test.c
cc -Wall -Werror -fstack-protector -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
-m32 -o test-m32 test.c
mkdir -p bug-dir
touch
bug-dir/111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
./test-native bug-dir
sizeof(struct dirent): 280
./test-m32 bug-dir
sizeof(struct dirent): 276
*** stack smashing detected ***: ./test-m32 terminated

Built on 32bit:
cc -Wall -Werror -fstack-protector -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
-o test-native test.c
cc -Wall -Werror -fstack-protector -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
-m32 -o test-m32 test.c
mkdir -p bug-dir
touch
bug-dir/111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
./test-native bug-dir
sizeof(struct dirent): 276
*** stack smashing detected ***: ./test-native terminated

/// test.c
#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <inttypes.h>

void func(const char*path) {
    struct dirent entry;
    struct dirent *result = NULL;
    int ret;

    DIR *dir = opendir(path);
    if(!dir) abort();
    printf("sizeof(struct dirent): %" PRIuFAST32 "\n", sizeof(entry));
    while (!(ret = readdir_r(dir, &entry, &result)) && result) {}
}

int main(int argc, const char** argv) {
    if(argc < 2) abort();
    func(argv[1]);
    return 0;
}