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std.c.dirent has incorrect field types for ino and off with 64-bit file offsets on linux #23622

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sno2 opened this issue Apr 20, 2025 · 0 comments · Fixed by #23637
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std.c.dirent has incorrect field types for ino and off with 64-bit file offsets on linux #23622

sno2 opened this issue Apr 20, 2025 · 0 comments · Fixed by #23637
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bug Observed behavior contradicts documented or intended behavior

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@sno2
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sno2 commented Apr 20, 2025

Zig Version

0.14.0

Steps to Reproduce and Observed Behavior

The following Zig program tries to use std.c.readdir to iterate through a directory.

const std = @import("std");

pub fn main() !void {
    const dir = std.c.opendir(".") orelse return error.OpenFailed;
    defer _ = std.c.closedir(dir);
    while (std.c.readdir(dir)) |entry| {
        std.log.info("null terminated={s}", .{std.mem.sliceTo(entry.name[0..], 0)});
        std.log.info("full={s}", .{entry.name});
    }
}

I would expect the null terminated=X to print out the name of the file, just like this C program:

#include <dirent.h>
#include <stdio.h>
#include <string.h>

int main() {
    DIR *dir = opendir(".");
    if (dir == NULL) {
        perror("opendir failed");
        return 1;
    }

    struct dirent *entry;
    while ((entry = readdir(dir)) != NULL) {
        printf("%s\n", entry->d_name);
    }

    closedir(dir);
    return 0;
}

Here is the result of running these programs:

$ ls
a.out  build.zig  build.zig.zon  main.c  src  zig-out

$ zig build run
info: null terminated=���v
                           
info: full=���v
�:P��Y+.���&�b� zig-outo��8�n��z�srcwF�
�.main.c�����$�r/a.out-��~��q��6build.zig.zon#��?&>�\w\build.zig�<�xE���|�..���������� .zig-cac
info: null terminated=��z�
�:P��Y+.���&�b�srcwF�
�.main.c�����$�r/a.out-��~��q��6build.zig.zon#��?&>�\w\build.zig�<�xE���|�..���������� .zig-cache
info: null terminated=P��Y+
info: full=P��Y+.���&�b�
�.main.c�����$�r/a.out-��~��q��6build.zig.zon#��?&>�\w\build.zig�<�xE���|�..���������� .zig-cache
info: null terminated=�
�. 
info: full=�
�.main.c�����$�r/a.out-��~��q��6build.zig.zon#��?&>�\w\build.zig�<�xE���|�..���������� .zig-cache
info: null terminated=$�r/ 
info: full=$�r/a.out-��~��q��6build.zig.zon#��?&>�\w\build.zig�<�xE���|�..���������� .zig-cache
info: null terminated=q��6(
info: full=q��6build.zig.zon#��?&>�\w\build.zig�<�xE���|�..���������� .zig-cache
info: null terminated=�\w\ 
info: full=�\w\build.zig�<�xE���|�..���������� .zig-cache
info: null terminated=��|�
info: full=��|�..���������� .zig-cache
info: null terminated=���� 
info: full=���� .zig-cache

Expected Behavior

I would expect both the null terminated=X to print the same value as for the C program:

$ gcc main.c && ./a.out
zig-out
src
.
main.c
a.out
build.zig.zon
build.zig
..
.zig-cache

Here is the dirent in source:

    extern struct {
        ino: c_uint,
        off: c_uint,
        reclen: c_ushort,
        type: u8,
        name: [256]u8,
    }

I think the ino and the off should sometimes be u64 and i64, respectively. For example, this Zig program works fine:

const std = @import("std");

const dirent = extern struct {
    ino: u64,
    off: i64,
    reclen: c_ushort,
    type: u8,
    name: [256]u8,
};

extern "c" fn readdir(dir: *std.c.DIR) ?*dirent;

pub fn main() !void {
    const dir = std.c.opendir(".") orelse return error.OpenFailed;
    defer _ = std.c.closedir(dir);
    while (readdir(dir)) |entry| {
        std.debug.print("{s}\n", .{std.mem.sliceTo(entry.name[0..], 0)});
    }
}
$ zig build run
zig-out
src
.
main.c
a.out
build.zig.zon
build.zig
..
.zig-cache

I am willing to contribute to the change, but I am unsure how to detect if we should be using 64-bit ino_t and off_t. For example, here is the code from glibc:

struct dirent
  {
#ifndef __USE_FILE_OFFSET64
    __ino_t d_ino;
    __off_t d_off;
#else
    __ino64_t d_ino;
    __off64_t d_off;
#endif
    unsigned short int d_reclen;
    unsigned char d_type;
    char d_name[256];		/* We must not include limits.h! */
  };

Thanks
@sno2 sno2 added the bug Observed behavior contradicts documented or intended behavior label Apr 20, 2025
@sno2 sno2 mentioned this issue Apr 21, 2025
Merged
@alexrp alexrp closed this as completed in 573d9aa Apr 26, 2025
tiawl pushed a commit to tiawl/zig that referenced this issue May 1, 2025
@sno2 @tiawl
std.c: use arch's ino_t and off_t for dirent
3f6b628 
Fixes ziglang#23622. The integer types used for these fields before would not
work on some platforms.
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std.c: use arch's ino_t and off_t for dirent sno2/zig
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