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author | A. Wilcox <awilcox@wilcox-tech.com> | 2018-02-01 22:05:36 +0000 |
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committer | A. Wilcox <awilcox@wilcox-tech.com> | 2018-02-01 22:05:36 +0000 |
commit | 88815225fdabe7fa862f1c07abfcc971fdf5b04e (patch) | |
tree | 7aaae7c04fcf06aea85505fc028f476a131b9c50 /loader | |
parent | c545f7393f0a10c182c2c085a36d7099b9c07a7f (diff) | |
parent | 78722ef403ffadcb78917e93e1859d43b9bf9df5 (diff) | |
download | gcompat-88815225fdabe7fa862f1c07abfcc971fdf5b04e.tar.gz gcompat-88815225fdabe7fa862f1c07abfcc971fdf5b04e.tar.bz2 gcompat-88815225fdabe7fa862f1c07abfcc971fdf5b04e.tar.xz gcompat-88815225fdabe7fa862f1c07abfcc971fdf5b04e.zip |
Merge branch 'patch-1' into 'master'
Clean up everything and add lots of new functions
I hope everything here is okay. I fixed some bugs in existing functions (mostly wrong prototypes or off-by-one errors) and formatted everything to a consistent style. If you'd like me to adjust the style, that's no problem. It wasn't very consistent to start with (within the code, and compared to the documentation).
*I added specific notes you may want to comment on to some of the commit messages.*
Major features:
* Pass correct `argv[0]` in loader
* Intercept `readlink("/proc/self/exe")` to allow re-exec
* Add almost all reasonable-to-implement functions in LSB 5.0.0 core generic libc. Remaining functions are:
- Impossible-to-implement: sigreturn
- Not useful: reentrant random (`*rand48_r`, etc.), argz, envz, pmap, rpc (clnt_*, svc*, xdr*), bindresvport
- Got tired of it: checked wchar
* Add additional functions used by android and its NDK tools (clang, cmake, lldb, ninja, etc.).
At this point, I am able to run Android Studio with the bundled prebuilt JDK, and compile, install, and run an android application (including one with native libraries) on a real device, with only a few minor issues:
* must export `LD_LIBRARY_PATH=/opt/android-studio/jre/jre/lib/amd64/server` because musl and glibc interpret the variable differently with regards to `dlopen`. This is something that has to be patched in musl builds of openjdk, so it's not a gcompat issue.
* ld.bfd fails to parse the argument `--sysroot=/path`, but can parse `--sysroot /path`. So there's some difference with `getopt_long_only` (or getopt in general). May be a bug, may be just an API difference. May be it can be patched up.
* LLDB fails to connect to the android phone for native debugging -- I haven't tried it on glibc yet, so it may not be a gcompat issue at all (may be a phone or the app issue).
I'd be happy to send some documentation later.
See merge request !1
Diffstat (limited to 'loader')
-rw-r--r-- | loader/loader.c | 98 |
1 files changed, 78 insertions, 20 deletions
diff --git a/loader/loader.c b/loader/loader.c index f2942a4..53a2c38 100644 --- a/loader/loader.c +++ b/loader/loader.c @@ -1,5 +1,6 @@ /* * Copyright (c) 2017 William Pitcock <nenolod@dereferenced.org> + * Copyright (c) 2018 Samuel Holland <samuel@sholland.org> * * Permission to use, copy, modify, and/or distribute this software for any * purpose with or without fee is hereby granted, provided that the above @@ -10,42 +11,99 @@ * from the use of this software. */ -#include <stdio.h> -#include <stdlib.h> -#include <string.h> -#include <unistd.h> -#include <limits.h> +#include <limits.h> /* PATH_MAX */ +#include <stddef.h> /* NULL */ +#include <stdio.h> /* fputs, fwrite, stderr */ +#include <stdlib.h> /* calloc, EXIT_FAILURE, getenv */ +#include <string.h> /* strcpy, strlcpy */ +#include <unistd.h> /* execve, ssize_t */ #ifndef PATH_MAX -#define PATH_MAX 16384 +#define PATH_MAX 16384 +#endif + +#ifndef LIBGCOMPAT +#error LIBGCOMPAT must be defined #endif #ifndef LINKER #error LINKER must be defined #endif -#ifndef LIBGCOMPAT -#error LIBGCOMPAT must be defined +#ifndef LOADER +#error LOADER must be defined #endif -int main(int argc, char *argv[], char *envp[]) { - size_t i = 0; +/* + * Given the argv { "foo", "bar", "baz" }, and the environment variable + * "LD_PRELOAD=/another/preload.so", the new argv will be { + * "ld-linux-$ARCH.so.N", + * "--argv0", + * "foo", + * "--preload", + * "/path/to/libgcompat.so /another/preload.so", + * "/path/to/foo", + * "bar", + * "baz" + * }. + * + * NOTE: The new argv needs 6 more entries than the original argc: five for + * arguments added at the beginning, and one for the NULL sentinel at the end + * not included in argc. Because calloc() is used, the sentinel is not + * explicitly set on its own, but *it is still there*! + * + * NOTE: The name given in argv[0] to musl *must* match glibc's ld.so filename. + * Many glibc-linked programs have an explicit dependency on its ld.so, but the + * file placed at that path (this loader) is not a real shared library. If musl + * tries to load this file as a shared library, it will fail. Thankfully, since + * musl treats argv[0] as "its" name when run directly, it considers a library + * by that name to already be loaded, and ignores the problematic dependency. + * + * NOTE: LD_PRELOAD entries are processed in order, and the environment variable + * is ignored if the parameter is given. In case the glibc-linked program needs + * another preloaded library, it should be appended to the argument so it gets + * loaded after libgcompat. Leave the environment variable as is, so if the + * program runs other glibc-linked programs, the same transformation gets + * applied there as well. + * + * NOTE: In order for the program to be able to re-exec itself it needs the + * fully-resolved path from /proc/self/exe ("target" below). This path is given + * to musl on the command line in new_argv[5], but it is not directly available + * to the program. An intercepted readlink("/proc/self/exe") must read it from + * /proc/self/cmdline. Thus, if its position in new_argv changes, that function + * must also be updated to match. + */ +int main(int argc, char *argv[], char *envp[]) +{ + char **new_argv = calloc(argc + 6, sizeof(char *)); + char preload[PATH_MAX]; char target[PATH_MAX]; - char **new_argv = calloc(sizeof(char *), argc + 5); + ssize_t i, j, len; - memset(target, 0, sizeof(target)); - if (readlink("/proc/self/exe", target, sizeof(target)) < 0) { + strcpy(preload, LIBGCOMPAT " "); + if (getenv("LD_PRELOAD") != NULL) { + len = strlcat(preload, getenv("LD_PRELOAD"), sizeof(preload)); + if ((size_t) len >= sizeof(preload)) { + fputs("too many preloaded libraries", stderr); + return EXIT_FAILURE; + } + } + + len = readlink("/proc/self/exe", target, sizeof(target)); + if (len < 0 || len == sizeof(target)) { perror("readlink"); return EXIT_FAILURE; } + target[len] = '\0'; - new_argv[0] = argv[0]; - new_argv[1] = "--preload"; - new_argv[2] = LIBGCOMPAT; - new_argv[3] = target; - - for (i = 1; i < argc; i++) { - new_argv[3 + i] = argv[i]; + new_argv[0] = LOADER; + new_argv[1] = "--argv0"; + new_argv[2] = argv[0]; + new_argv[3] = "--preload"; + new_argv[4] = preload; + new_argv[5] = target; + for (i = 6, j = 1; j < argc; ++i, ++j) { + new_argv[i] = argv[j]; } execve(LINKER, new_argv, envp); |