nixpkgs-suyu/pkgs/development/tools/misc/saleae-logic/preload.c

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/*
* LD_PRELOAD trick to make Saleae Logic work from a read-only installation
* directory.
*
* Saleae Logic tries to write to a few directories inside its installation
* directory. Because the Nix store is read-only, we have to redirect access to
* this file somewhere else. Here's the map:
*
* $out/Settings/ => $HOME/.saleae-logic/Settings/
* $out/Databases/ => $HOME/.saleae-logic/Databases/
* $out/Errors/ => $HOME/.saleae-logic/Errors/
* $out/Calibration/ => $HOME/.saleae-logic/Calibration/
*
* This also makes the software multi-user aware :-)
*
* NOTE: AFAIK (Bjørn Forsman), Logic version 1.2+ was supposed to have a
* command line parameter for redirecting these write operations, but
* apparently that feature got postponed.
*
* Usage:
* gcc -shared -fPIC -DOUT="$out" preload.c -o preload.so -ldl
* LD_PRELOAD=$PWD/preload.so ./result/Logic
*
* To see the paths that are modified at runtime, set the environment variable
* PRELOAD_DEBUG to 1 (or anything really; debugging is on as long as the
* variable exists).
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <dlfcn.h>
#include <limits.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <errno.h>
#ifndef OUT
#error Missing OUT define - path to the installation directory.
#endif
/*
* TODO: How to properly wrap "open", which is declared as a variadic function
* in glibc? The man page lists these signatures:
*
* int open(const char *pathname, int flags);
* int open(const char *pathname, int flags, mode_t mode);
*
* But using either signature in this code cause a compile error, because
* glibc has declared the function as "int open(const char *, int, ...)".
* Same thing with "openat".
*
* For now we discard the variadic args. It seems to work.
*
* Relevant:
* http://stackoverflow.com/questions/28462523/how-to-wrap-ioctlint-d-unsigned-long-request-using-ld-preload
*/
typedef FILE *(*fopen_func_t)(const char *path, const char *mode);
typedef FILE *(*fopen64_func_t)(const char *path, const char *mode);
typedef int (*open_func_t)(const char *pathname, int flags, ...);
typedef int (*open64_func_t)(const char *pathname, int flags, ...);
typedef int (*openat_func_t)(int dirfd, const char *pathname, int flags, ...);
typedef int (*openat64_func_t)(int dirfd, const char *pathname, int flags, ...);
typedef int (*xstat_func_t)(int vers, const char *pathname, struct stat *buf);
typedef int (*xstat64_func_t)(int vers, const char *pathname, struct stat64 *buf);
typedef int (*access_func_t)(const char *pathname, int mode);
typedef int (*faccessat_func_t)(int dirfd, const char *pathname, int mode, int flags);
typedef int (*unlink_func_t)(const char *pathname);
/*
* Redirect $out/{Settings,Databases,Errors,Calibration}/ => $HOME/.saleae-logic/.
* Path is truncated if bigger than PATH_MAX.
*
* @param pathname Original file path.
* @param buffer Pointer to a buffer of size PATH_MAX bytes that this function
* will write the new redirected path to (if needed).
*
* @return Pointer to the resulting path. It will either be equal to the
* pathname (no redirect) or buffer argument (was redirected).
*/
static const char *redirect(const char *pathname, char *buffer)
{
const char *homepath;
const char *new_path;
static char have_warned;
const char *remainder;
static char have_initialized;
static size_t out_strlen;
static size_t settings_strlen;
static size_t databases_strlen;
static size_t errors_strlen;
static size_t calibration_strlen;
int ret;
int i;
homepath = getenv("HOME");
if (!homepath) {
homepath = "/";
if (!have_warned && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: WARNING: HOME is unset, using \"/\" (root) instead.\n");
have_warned = 1;
}
}
if (!have_initialized) {
/*
* The directories that Saleae Logic expects to find.
* The first element is intentionally empty (create base dir).
*/
char *dirs[] = {"", "/Settings", "/Databases", "/Errors", "/Calibration"};
char old_settings_path[PATH_MAX];
access_func_t orig_access;
out_strlen = strlen(OUT);
settings_strlen = out_strlen + strlen("/Settings");
databases_strlen = out_strlen + strlen("/Databases");
errors_strlen = out_strlen + strlen("/Errors");
calibration_strlen = out_strlen + strlen("/Calibration");
for (i = 0; i < sizeof dirs / sizeof dirs[0]; i++) {
snprintf(buffer, PATH_MAX, "%s/.saleae-logic%s", homepath, dirs[i]);
buffer[PATH_MAX-1] = '\0';
ret = mkdir(buffer, 0755);
if (0 != ret && errno != EEXIST) {
fprintf(stderr, "ERROR: Failed to create directory \"%s\": %s\n",
buffer, strerror(errno));
return NULL;
}
}
/*
* Automatic migration of the settings file:
* ~/.saleae-logic-settings.xml => ~/.saleae-logic/Settings/settings.xml
*/
snprintf(old_settings_path, PATH_MAX, "%s/.saleae-logic-settings.xml", homepath);
old_settings_path[PATH_MAX-1] = '\0';
orig_access = (access_func_t)dlsym(RTLD_NEXT, "access");
if (orig_access(old_settings_path, F_OK) == 0) {
snprintf(buffer, PATH_MAX, "%s/.saleae-logic/Settings/settings.xml", homepath);
buffer[PATH_MAX-1] = '\0';
ret = rename(old_settings_path, buffer);
if (ret != 0) {
fprintf(stderr, "WARN: Failed to move %s to %s",
old_settings_path, buffer);
}
}
have_initialized = 1;
}
new_path = pathname;
remainder = pathname + out_strlen;
if ((strncmp(OUT "/Settings", pathname, settings_strlen) == 0) ||
(strncmp(OUT "/Databases", pathname, databases_strlen) == 0) ||
(strncmp(OUT "/Errors", pathname, errors_strlen) == 0) ||
(strncmp(OUT "/Calibration", pathname, calibration_strlen) == 0)) {
snprintf(buffer, PATH_MAX, "%s/.saleae-logic%s", homepath, remainder);
buffer[PATH_MAX-1] = '\0';
new_path = buffer;
}
return new_path;
}
FILE *fopen(const char *pathname, const char *mode)
{
const char *path;
char buffer[PATH_MAX];
fopen_func_t orig_fopen;
orig_fopen = (fopen_func_t)dlsym(RTLD_NEXT, "fopen");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: fopen(\"%s\", \"%s\") => \"%s\"\n", pathname, mode, path);
}
return orig_fopen(path, mode);
}
FILE *fopen64(const char *pathname, const char *mode)
{
const char *path;
char buffer[PATH_MAX];
fopen64_func_t orig_fopen64;
orig_fopen64 = (fopen64_func_t)dlsym(RTLD_NEXT, "fopen64");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: fopen64(\"%s\", \"%s\") => \"%s\"\n", pathname, mode, path);
}
return orig_fopen64(path, mode);
}
int open(const char *pathname, int flags, ...)
{
const char *path;
char buffer[PATH_MAX];
open_func_t orig_open;
orig_open = (open_func_t)dlsym(RTLD_NEXT, "open");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: open(\"%s\", ...) => \"%s\"\n", pathname, path);
}
return orig_open(path, flags);
}
int open64(const char *pathname, int flags, ...)
{
const char *path;
char buffer[PATH_MAX];
open64_func_t orig_open64;
orig_open64 = (open64_func_t)dlsym(RTLD_NEXT, "open64");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: open64(\"%s\", ...) => \"%s\"\n", pathname, path);
}
return orig_open64(path, flags);
}
int openat(int dirfd, const char *pathname, int flags, ...)
{
const char *path;
char buffer[PATH_MAX];
openat_func_t orig_openat;
orig_openat = (openat_func_t)dlsym(RTLD_NEXT, "openat");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: openat(%d, \"%s\", %#x) => \"%s\"\n", dirfd, pathname, flags, path);
}
return orig_openat(dirfd, path, flags);
}
int openat64(int dirfd, const char *pathname, int flags, ...)
{
const char *path;
char buffer[PATH_MAX];
openat64_func_t orig_openat64;
orig_openat64 = (openat64_func_t)dlsym(RTLD_NEXT, "openat64");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: openat64(%d, \"%s\", %#x) => \"%s\"\n", dirfd, pathname, flags, path);
}
return orig_openat64(dirfd, path, flags);
}
/*
* Notes about "stat".
*
* The stat function is special, at least in glibc, in that it cannot be
* directly overridden by LD_PRELOAD, due to it being inline wrapper around
* __xstat. The __xstat functions take one extra parameter, a version number,
* to indicate what "struct stat" should look like. This trick allows changing
* the contents of mode_t without changing the shared library major number. See
* sys/stat.h header for more info.
*/
int __xstat(int vers, const char *pathname, struct stat *buf)
{
const char *path;
char buffer[PATH_MAX];
xstat_func_t orig_xstat;
orig_xstat = (xstat_func_t)dlsym(RTLD_NEXT, "__xstat");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: (__x)stat(\"%s\", ...) => \"%s\"\n", pathname, path);
}
return orig_xstat(vers, path, buf);
}
int __xstat64(int vers, const char *pathname, struct stat64 *buf)
{
const char *path;
char buffer[PATH_MAX];
xstat64_func_t orig_xstat64;
orig_xstat64 = (xstat64_func_t)dlsym(RTLD_NEXT, "__xstat64");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: (__x)stat64(\"%s\", ...) => \"%s\"\n", pathname, path);
}
return orig_xstat64(vers, path, buf);
}
int access(const char *pathname, int mode)
{
const char *path;
char buffer[PATH_MAX];
access_func_t orig_access;
orig_access = (access_func_t)dlsym(RTLD_NEXT, "access");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: access(\"%s\", ...) => \"%s\"\n", pathname, path);
}
return orig_access(path, mode);
}
int faccessat(int dirfd, const char *pathname, int mode, int flags)
{
const char *path;
char buffer[PATH_MAX];
faccessat_func_t orig_faccessat;
orig_faccessat = (faccessat_func_t)dlsym(RTLD_NEXT, "faccessat");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: faccessat(\"%s\", ...) => \"%s\"\n", pathname, path);
}
return orig_faccessat(dirfd, path, mode, flags);
}
int unlink(const char *pathname)
{
const char *path;
char buffer[PATH_MAX];
unlink_func_t orig_unlink;
orig_unlink = (unlink_func_t)dlsym(RTLD_NEXT, "unlink");
path = redirect(pathname, buffer);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: unlink(\"%s\") => \"%s\"\n", pathname, path);
}
return orig_unlink(path);
}