tjh.dev
1/*
2 * LD_PRELOAD trick to make Eagle (schematic editor and PCB layout tool from
3 * CadSoft) work from a read-only installation directory.
4 *
5 * When Eagle starts, it looks for the license file in <eagle>/bin/eagle.key
6 * (where <eagle> is the install path). If eagle.key is not found, Eagle checks
7 * for write access to <eagle>/bin/, shows a license dialog to the user and
8 * then attempts to write a license file to <eagle>/bin/.
9 *
10 * This will of course fail when Eagle is installed in the read-only Nix store.
11 * Hence this library that redirects accesses to the those paths in the
12 * following way:
13 *
14 * <eagle>/bin => $HOME
15 * <eagle>/bin/eagle.key => $HOME/.eagle.key
16 *
17 * Also, if copying an example project to ~/eagle/ (in the Eagle GUI), Eagle
18 * chmod's the destination with read-only permission bits (presumably because
19 * the source is read-only) and fails to complete the copy operation.
20 * Therefore, the mode argument in calls to chmod() is OR'ed with the S_IWUSR
21 * bit (write by owner).
22 *
23 * Usage:
24 * gcc -shared -fPIC -DEAGLE_PATH="$out/eagle-${version}" eagle_fixer.c -o eagle_fixer.so -ldl
25 * LD_PRELOAD=$PWD/eagle_fixer.so ./result/bin/eagle
26 *
27 * To see the paths that are modified at runtime, set the environment variable
28 * EAGLE_FIXER_DEBUG to 1.
29 */
30
31#define _GNU_SOURCE
32#include <stdio.h>
33#include <stdlib.h>
34#include <string.h>
35#include <unistd.h>
36#include <fcntl.h>
37#include <dlfcn.h>
38#include <limits.h>
39#include <sys/stat.h>
40
41#ifndef EAGLE_PATH
42#error Missing EAGLE_PATH, path to the eagle-${version} installation directory.
43#endif
44
45typedef FILE *(*fopen_func_t)(const char *path, const char *mode);
46typedef int (*access_func_t)(const char *pathname, int mode);
47typedef int (*chmod_func_t)(const char *path, mode_t mode);
48
49/*
50 * Map <eagle>/bin to $HOME and <eagle>/bin/eagle.key to $HOME/.eagle.key
51 *
52 * Path is truncated if bigger than PATH_MAX. It's not threadsafe, but that's
53 * OK.
54 */
55static const char *redirect(const char *pathname)
56{
57 static char buffer[PATH_MAX];
58 const char *homepath;
59 const char *new_path;
60 static int have_warned;
61
62 homepath = getenv("HOME");
63 if (!homepath) {
64 homepath = "/";
65 if (!have_warned && getenv("EAGLE_FIXER_DEBUG")) {
66 fprintf(stderr, "eagle_fixer: HOME is unset, using \"/\" (root) instead.\n");
67 have_warned = 1;
68 }
69 }
70
71 new_path = pathname;
72 if (strcmp(EAGLE_PATH "/bin", pathname) == 0) {
73 /* redirect to $HOME */
74 new_path = homepath;
75 } else if (strcmp(EAGLE_PATH "/bin/eagle.key", pathname) == 0) {
76 /* redirect to $HOME/.eagle.key */
77 snprintf(buffer, PATH_MAX, "%s/.eagle.key", homepath);
78 buffer[PATH_MAX-1] = '\0';
79 new_path = buffer;
80 }
81
82 return new_path;
83}
84
85FILE *fopen(const char *pathname, const char *mode)
86{
87 FILE *fp;
88 const char *path;
89 fopen_func_t orig_fopen;
90
91 orig_fopen = (fopen_func_t)dlsym(RTLD_NEXT, "fopen");
92 path = redirect(pathname);
93 fp = orig_fopen(path, mode);
94
95 if (path != pathname && getenv("EAGLE_FIXER_DEBUG")) {
96 fprintf(stderr, "eagle_fixer: fopen(\"%s\", \"%s\") => \"%s\": fp=%p\n", pathname, mode, path, fp);
97 }
98
99 return fp;
100}
101
102int access(const char *pathname, int mode)
103{
104 int ret;
105 const char *path;
106 access_func_t orig_access;
107
108 orig_access = (access_func_t)dlsym(RTLD_NEXT, "access");
109 path = redirect(pathname);
110 ret = orig_access(path, mode);
111
112 if (path != pathname && getenv("EAGLE_FIXER_DEBUG")) {
113 fprintf(stderr, "eagle_fixer: access(\"%s\", %d) => \"%s\": ret=%d\n", pathname, mode, path, ret);
114 }
115
116 return ret;
117}
118
119int chmod(const char *pathname, mode_t mode)
120{
121 int ret;
122 mode_t new_mode;
123 chmod_func_t orig_chmod;
124
125 orig_chmod = (chmod_func_t)dlsym(RTLD_NEXT, "chmod");
126 new_mode = mode | S_IWUSR;
127 ret = orig_chmod(pathname, new_mode);
128
129 if (getenv("EAGLE_FIXER_DEBUG")) {
130 fprintf(stderr, "eagle_fixer: chmod(\"%s\", %o) => %o: ret=%d\n", pathname, mode, new_mode, ret);
131 }
132
133 return ret;
134}