fstat not return right file-size when compile it with -m32

[bitbegin]

Environment

Microsoft Windows [Version 10.0.20236.1005]
(c) 2020 Microsoft Corporation. All rights reserved.

Release:        20.04
Linux version 4.19.128-microsoft-standard (oe-user@oe-host) (gcc version 8.2.0 (GCC)) #1 SMP Tue Jun 23 12:58:10 UTC 2020

Steps to reproduce

prepare tools:

sudo dpkg --add-architecture i386
sudo apt-get update
sudo apt-get install libc6:i386

sudo apt-get install gcc
sudo apt-get install gcc-multilib

source code:

#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[]) {
    char *infile;
    int fd;
    struct stat finfo;
    if (argc != 2)
    {
            fprintf(stderr, "Too many arguments.\n");
            exit(1);
    }

    infile = argv[1];
    fd = open(infile, O_RDONLY);

    fstat(fd, &finfo);
    printf("file: %s, size: %ld\n", infile, finfo.st_size);
}

compile it with gcc -o test test.c, and run ./test test.c, get file: test.c, size: 418, it's right;

compile it with gcc -m32 -o test test.c, and run ./test test.c, get file: test.c, size: -135036928, it's not right!

Expected behavior

the result with -m32 flag should also right.

Actual behavior

fstat not return right file-size when compile it with -m32.

[hiiamboris]

Worth noting: wrong results are only returned for files on (auto)mounted Windows partitions. That is, for the above test to fail you have to place test.c anywhere in /mnt/c/ or similar path.

[bitbegin]

if you run it in ~/ folder, return size ok. if you run it in other place like /mnt/d, the size will be not right

[therealkenc]

Thanks for the submission and the nice repro. Interesting catch; was able to reproduce. Fascinatingly, the program has the same behavior on a Real Linux™ box with a mounted CIFS share to Windows.

Note the fstat64(2) does return 418. I've tried for a couple of hours to justify the behavior, but cannot. It is unexpected behavior alright, but also not unique to WSL.

[microsoft-github-policy-service]

This issue has been automatically closed since it has not had any activity for the past year. If you're still experiencing this issue please re-file this as a new issue or feature request.

Thank you!