patchelf breaks hardlinks

[sjackman]

Hard links are used extensively by gcc and git. See the example below.

Experiment

$ cc hello.c -o hello
$ ln hello hello2
$ ls -il hello hello2
10099869 -rwxr-xr-x 2 sjackman assembly 7130 Aug 22 13:54 hello
10099869 -rwxr-xr-x 2 sjackman assembly 7130 Aug 22 13:54 hello2
$ patchelf --set-rpath /foo hello

Observed

$ ls -il hello hello2
10099870 -rwxr-xr-x 1 sjackman assembly 11226 Aug 22 13:55 hello
10099869 -rwxr-xr-x 1 sjackman assembly  7130 Aug 22 13:54 hello2

Expected

$ ls -il hello hello2
10099869 -rwxr-xr-x 2 sjackman assembly 11226 Aug 22 13:55 hello
10099869 -rwxr-xr-x 2 sjackman assembly 11226 Aug 22 13:55 hello2

[darealshinji]

patchelf writes the changes in a new temporary file and replaces the original with the new one, that's why this happens.
https://github.com/NixOS/patchelf/blob/master/src/patchelf.cc#L378

[sjackman]

Breaking hardlinks is rather unexpected behaviour. Can writeFile be changed to write directly to the file, rather than through a temp file?

[darealshinji]

I found the solution! This is what "static void writeFile()" should look like:

static void writeFile(string fileName, mode_t fileMode)
{
    int fd = open(fileName.c_str(), O_TRUNC | O_WRONLY, 0700);
    if (fd == -1)
        error("open");

    if (write(fd, contents, fileSize) != fileSize)
        error("write");

    if (close(fd) != 0)
        error("close");
}

darealshinji@bed9cea

[sjackman]

Excellent! Thanks. I'll test it soon. Without O_CREAT you can remove , 0700 as it has no effect.

[sjackman]

@edolstra Can you please merge this patch from @darealshinji to fix this issue? Thanks!
darealshinji@bed9cea

[sjackman]

Great. Thanks. Will there be a new stable release that includes this fix?