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When an executable is invoked directly, we calculate $ORIGIN by calling
readlink on /proc/self/exe, which the Linux kernel resolves to the
target of any symlinks. However, if an executable is run through ld.so,
we cannot use /proc/self/exe and instead use the path given as an
argument. This leads to a different calculation of $ORIGIN, which is
most notable in that it causes ldd to behave differently (e.g., by not
finding a library) from directly running the program.
To make the behavior consistent, take advantage of the fact that the
kernel also resolves /proc/self/fd/ symlinks to the target of any
symlinks in the same manner, so once we have opened the main executable
in order to load it, replace the user-provided path with the result of
calling readlink("/proc/self/fd/N").
(On non-Linux platforms this resolution does not happen and so no
behavior change is needed.)
The __fd_to_filename requires _fitoa_word and _itoa_word, which for
32-bits pulls a lot of definitions from _itoa.c (due _ITOA_NEEDED
being defined). To simplify the build move the required function
to a new file, _fitoa_word.c.
Checked on x86_64-linux-gnu and i686-linux-gnu.
Co-authored-by: Geoffrey Thomas <geofft@ldpreload.com>
Reviewed-by: Geoffrey Thomas <geofft@ldpreload.com>
Tested-by: Geoffrey Thomas <geofft@ldpreload.com>
98 lines
2.9 KiB
C
98 lines
2.9 KiB
C
/* Find path of executable.
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Copyright (C) 1998-2025 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <assert.h>
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#include <dl-dst.h>
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#include <fcntl.h>
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#include <ldsodefs.h>
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#include <sysdep.h>
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#include <fd_to_filename.h>
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/* On Linux >= 2.1 systems which have the dcache implementation we can get
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the path of the application from the /proc/self/exe symlink. Try this
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first and fall back on the generic method if necessary. */
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const char *
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_dl_get_origin (void)
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{
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char linkval[PATH_MAX];
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char *result;
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int len;
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len = INTERNAL_SYSCALL_CALL (readlinkat, AT_FDCWD, "/proc/self/exe",
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linkval, sizeof (linkval));
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if (len > 0 && linkval[0] != '[')
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{
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/* We can use this value. */
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assert (linkval[0] == '/');
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while (len > 1 && linkval[len - 1] != '/')
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--len;
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result = (char *) malloc (len + 1);
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if (result == NULL)
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result = (char *) -1;
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else if (len == 1)
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memcpy (result, "/", 2);
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else
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*((char *) __mempcpy (result, linkval, len - 1)) = '\0';
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}
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else
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{
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result = (char *) -1;
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/* We use the environment variable LD_ORIGIN_PATH. If it is set make
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a copy and strip out trailing slashes. */
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if (GLRO(dl_origin_path) != NULL)
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{
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size_t len = strlen (GLRO(dl_origin_path));
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result = (char *) malloc (len + 1);
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if (result == NULL)
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result = (char *) -1;
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else
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{
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char *cp = __mempcpy (result, GLRO(dl_origin_path), len);
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while (cp > result + 1 && cp[-1] == '/')
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--cp;
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*cp = '\0';
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}
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}
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}
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return result;
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}
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/* On Linux, readlink on the magic symlinks in /proc/self/fd also has
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the same behavior of returning the canonical path from the dcache.
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If it does not work, we do not bother to canonicalize. */
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char *
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_dl_canonicalize (int fd)
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{
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struct fd_to_filename fdfilename;
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char canonical[PATH_MAX];
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char *path = __fd_to_filename (fd, &fdfilename);
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int size = INTERNAL_SYSCALL_CALL (readlinkat, AT_FDCWD, path,
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canonical, PATH_MAX - 1);
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/* Check if the path was truncated. */
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if (size >= 0 && size < PATH_MAX - 1)
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{
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canonical[size] = '\0';
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return __strdup (canonical);
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}
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return NULL;
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}
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