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glibc will look for a /nix/store/HASH-PACKAGE-VERSION/etc/ld.so.cache to provide a mapping of libraries to absolute paths, resolved during the patchelf fixup phase hook.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,144 @@ | ||
| Adopted from | ||
| https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/patches/glibc-dl-cache.patch?h=core-updates&id=0236013cd0fc86ff4a042885c735e3f36a7f5c25 | ||
| and https://guix.gnu.org/blog/2021/taming-the-stat-storm-with-a-loader-cache/ | ||
|
|
||
| Read the shared library cache relative to $ORIGIN instead of reading | ||
| from /etc/ld.so.cache. Also arrange so that this cache takes | ||
| precedence over RUNPATH. | ||
|
|
||
| diff --git a/elf/dl-cache.c b/elf/dl-cache.c | ||
| index 93d185e788..e0760a1f40 100644 | ||
| --- a/elf/dl-cache.c | ||
| +++ b/elf/dl-cache.c | ||
| @@ -171,6 +171,51 @@ _dl_cache_libcmp (const char *p1, const char *p2) | ||
| return *p1 - *p2; | ||
| } | ||
|
|
||
| +/* Special value representing the lack of an ld.so cache. */ | ||
| +static const char ld_so_cache_lacking[] = "/ld.so cache is lacking"; | ||
| + | ||
| +/* Return the per-application ld.so cache, relative to $ORIGIN, or NULL if | ||
| + that fails for some reason. Do not return the system-wide LD_SO_CACHE | ||
| + since on a foreign distro it would contain invalid information. */ | ||
| +static const char * | ||
| +ld_so_cache (void) | ||
| +{ | ||
| + static const char *loader_cache; | ||
| + | ||
| + if (loader_cache == NULL) | ||
| + { | ||
| + static const char store[] = "@nixStoreDir@"; | ||
| + const char *origin = _dl_get_origin (); | ||
| + | ||
| + /* Check whether ORIGIN is something like "/gnu/store/…-foo/bin". */ | ||
| + if (strncmp (store, origin, strlen (store)) == 0 | ||
| + && origin[sizeof store - 1] == '/') | ||
| + { | ||
| + char *store_item_end = strchr (origin + sizeof store, '/'); | ||
| + | ||
| + if (store_item_end != NULL) | ||
| + { | ||
| + static const char suffix[] = "/etc/ld.so.cache"; | ||
| + size_t store_item_len = store_item_end - origin; | ||
| + | ||
| + /* Note: We can't use 'malloc' because it can be interposed. | ||
| + Likewise, 'strncpy' is not available. */ | ||
| + char *cache = alloca (strlen (origin) + sizeof suffix); | ||
| + | ||
| + strcpy (cache, origin); | ||
| + strcpy (cache + store_item_len, suffix); | ||
| + | ||
| + loader_cache = __strdup (cache) ?: ld_so_cache_lacking; | ||
| + } | ||
| + else | ||
| + loader_cache = ld_so_cache_lacking; | ||
| + } | ||
| + else | ||
| + loader_cache = ld_so_cache_lacking; | ||
| + } | ||
| + | ||
| + return loader_cache; | ||
| +} | ||
|
|
||
| /* Look up NAME in ld.so.cache and return the file name stored there, or null | ||
| if none is found. The cache is loaded if it was not already. If loading | ||
| @@ -190,12 +235,15 @@ _dl_load_cache_lookup (const char *name) | ||
|
|
||
| /* Print a message if the loading of libs is traced. */ | ||
| if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS)) | ||
| - _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE); | ||
| + _dl_debug_printf (" search cache=%s\n", ld_so_cache ()); | ||
| + | ||
| + if (__glibc_unlikely (ld_so_cache () == ld_so_cache_lacking)) | ||
| + return NULL; | ||
|
|
||
| if (cache == NULL) | ||
| { | ||
| /* Read the contents of the file. */ | ||
| - void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize, | ||
| + void *file = _dl_sysdep_read_whole_file (ld_so_cache (), &cachesize, | ||
| PROT_READ); | ||
|
|
||
| /* We can handle three different cache file formats here: | ||
| diff --git a/elf/dl-load.c b/elf/dl-load.c | ||
| index f3201e7c14..a69aec3428 100644 | ||
| --- a/elf/dl-load.c | ||
| +++ b/elf/dl-load.c | ||
| @@ -2152,28 +2152,6 @@ _dl_map_object (struct link_map *loader, const char *name, | ||
| loader ?: GL(dl_ns)[LM_ID_BASE]._ns_loaded, | ||
| LA_SER_LIBPATH, &found_other_class); | ||
|
|
||
| - /* Look at the RUNPATH information for this binary. */ | ||
| - if (fd == -1 && loader != NULL | ||
| - && cache_rpath (loader, &loader->l_runpath_dirs, | ||
| - DT_RUNPATH, "RUNPATH")) | ||
| - fd = open_path (name, namelen, mode, | ||
| - &loader->l_runpath_dirs, &realname, &fb, loader, | ||
| - LA_SER_RUNPATH, &found_other_class); | ||
| - | ||
| - if (fd == -1) | ||
| - { | ||
| - realname = _dl_sysdep_open_object (name, namelen, &fd); | ||
| - if (realname != NULL) | ||
| - { | ||
| - fd = open_verify (realname, fd, | ||
| - &fb, loader ?: GL(dl_ns)[nsid]._ns_loaded, | ||
| - LA_SER_CONFIG, mode, &found_other_class, | ||
| - false); | ||
| - if (fd == -1) | ||
| - free (realname); | ||
| - } | ||
| - } | ||
| - | ||
| #ifdef USE_LDCONFIG | ||
| if (fd == -1 | ||
| && (__glibc_likely ((mode & __RTLD_SECURE) == 0) | ||
| @@ -2232,6 +2210,28 @@ _dl_map_object (struct link_map *loader, const char *name, | ||
| } | ||
| #endif | ||
|
|
||
| + /* Look at the RUNPATH information for this binary. */ | ||
| + if (fd == -1 && loader != NULL | ||
| + && cache_rpath (loader, &loader->l_runpath_dirs, | ||
| + DT_RUNPATH, "RUNPATH")) | ||
| + fd = open_path (name, namelen, mode, | ||
| + &loader->l_runpath_dirs, &realname, &fb, loader, | ||
| + LA_SER_RUNPATH, &found_other_class); | ||
| + | ||
| + if (fd == -1) | ||
| + { | ||
| + realname = _dl_sysdep_open_object (name, namelen, &fd); | ||
| + if (realname != NULL) | ||
| + { | ||
| + fd = open_verify (realname, fd, | ||
| + &fb, loader ?: GL(dl_ns)[nsid]._ns_loaded, | ||
| + LA_SER_CONFIG, mode, &found_other_class, | ||
| + false); | ||
| + if (fd == -1) | ||
| + free (realname); | ||
| + } | ||
| + } | ||
| + | ||
| /* Finally, try the default path. */ | ||
| if (fd == -1 | ||
| && ((l = loader ?: GL(dl_ns)[nsid]._ns_loaded) == NULL |
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