115 lines
3.2 KiB
C
115 lines
3.2 KiB
C
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/*
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* LD_PRELOAD trick to make Saleae Logic work from a read-only installation
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* directory.
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*
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* Saleae Logic tries to write to the ./Settings/settings.xml file, relative to
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* its installation directory. Because the nix store is read-only, we have to
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* redirect access to this file somewhere else. Here's the map:
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*
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* $out/Settings/settings.xml => $HOME/.saleae-logic-settings.xml
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*
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* This also makes the software multi-user aware :-)
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*
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* NOTE: The next Logic version is supposed to have command line parameters for
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* configuring where the Settings/ directory is located, but until then we have
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* to use this.
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*
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* Usage:
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* gcc -shared -fPIC -DOUT="$out" preload.c -o preload.so -ldl
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* LD_PRELOAD=$PWD/preload.so ./result/Logic
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*
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* To see the paths that are modified at runtime, set the environment variable
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* PRELOAD_DEBUG to 1 (or anything really; debugging is on as long as the
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* variable exists).
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*/
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#define _GNU_SOURCE
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <dlfcn.h>
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#include <limits.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#ifndef OUT
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#error Missing OUT define - path to the installation directory.
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#endif
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typedef FILE *(*fopen_func_t)(const char *path, const char *mode);
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typedef FILE *(*fopen64_func_t)(const char *path, const char *mode);
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/*
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* Redirect $out/Settings/settings.xml => $HOME/.saleae-logic-settings.xml. No
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* other paths are changed. Path is truncated if bigger than PATH_MAX.
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*
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* @param pathname Original file path.
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* @param buffer Pointer to a buffer of size PATH_MAX bytes that this function
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* will write the new redirected path to (if needed).
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*
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* @return Pointer to the resulting path. It will either be equal to the
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* pathname or buffer argument.
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*/
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static const char *redirect(const char *pathname, char *buffer)
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{
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const char *homepath;
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const char *new_path;
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static char have_warned;
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homepath = getenv("HOME");
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if (!homepath) {
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homepath = "/";
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if (!have_warned && getenv("PRELOAD_DEBUG")) {
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fprintf(stderr, "preload_debug: WARNING: HOME is unset, using \"/\" (root) instead.\n");
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have_warned = 1;
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}
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}
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new_path = pathname;
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if (strcmp(OUT "/Settings/settings.xml", pathname) == 0) {
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snprintf(buffer, PATH_MAX, "%s/.saleae-logic-settings.xml", homepath);
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buffer[PATH_MAX-1] = '\0';
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new_path = buffer;
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}
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return new_path;
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}
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FILE *fopen(const char *pathname, const char *mode)
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{
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FILE *fp;
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const char *path;
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char buffer[PATH_MAX];
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fopen_func_t orig_fopen;
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orig_fopen = (fopen_func_t)dlsym(RTLD_NEXT, "fopen");
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path = redirect(pathname, buffer);
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fp = orig_fopen(path, mode);
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if (path != pathname && getenv("PRELOAD_DEBUG")) {
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fprintf(stderr, "preload_debug: fopen(\"%s\", \"%s\") => \"%s\": fp=%p\n", pathname, mode, path, fp);
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}
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return fp;
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}
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FILE *fopen64(const char *pathname, const char *mode)
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{
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FILE *fp;
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const char *path;
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char buffer[PATH_MAX];
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fopen64_func_t orig_fopen64;
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orig_fopen64 = (fopen64_func_t)dlsym(RTLD_NEXT, "fopen64");
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path = redirect(pathname, buffer);
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fp = orig_fopen64(path, mode);
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if (path != pathname && getenv("PRELOAD_DEBUG")) {
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fprintf(stderr, "preload_debug: fopen64(\"%s\", \"%s\") => \"%s\": fp=%p\n", pathname, mode, path, fp);
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}
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return fp;
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}
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