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There is a lot to explain, but I try to make it as short as possible. I'd start by pasting some parts of sys/stat.h: extern int stat (const char *__restrict __file, struct stat *__restrict __buf) __THROW __nonnull ((1, 2)); extern int __REDIRECT_NTH (stat, (const char *__restrict __file, struct stat *__restrict __buf), stat64) __nonnull ((1, 2)); __extern_inline int __NTH (stat (const char *__path, struct stat *__statbuf)) { return __xstat (_STAT_VER, __path, __statbuf); } Only one of these is effective at once, due to some usage of the mess we are dealing with in here. So, basically, while compiling or linking stat() in our code can be transformed into some other func. Or a dragon. Now, if you read stat(2) manpage, esp. "C library/kernel differences" section, you'll learn that glibc uses some tricks for older applications to work. I haven't gotten around actual code that does this, but based on my observations, if 'stat' symbol is found, glibc assumes it's dealing with ancient application. Unfortunately, it can be just ours stat coming from our mock. Therefore, calling stat() from a test will end up in our mock. But since glibc is not exposing the symbol anymore, our call of real_stat() will SIGSEGV immediately as the pointer to function is NULL. Therefore, we should expose only those symbols we know glibc has. Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
325 lines
7.6 KiB
C
325 lines
7.6 KiB
C
/*
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* Copyright (C) 2016 Red Hat, Inc.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library. If not, see
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* <http://www.gnu.org/licenses/>.
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*
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* Author: Michal Privoznik <mprivozn@redhat.com>
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*/
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#include <config.h>
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#include "virmock.h"
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#include <unistd.h>
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#include <sys/types.h>
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#include <fcntl.h>
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#include <execinfo.h>
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#include <sys/file.h>
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#include <sys/stat.h>
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#include "internal.h"
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#include "configmake.h"
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#include "virstring.h"
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#include "viralloc.h"
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#include "virfile.h"
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/* stat can be a macro as follows:
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*
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* #define stat stat64
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*
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* This wouldn't fly with our mock. Make sure that the macro (and
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* all its friends) are undefined. We don't want anybody mangling
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* our code. */
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#undef stat
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#undef stat64
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#undef __xstat
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#undef __xstat64
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#undef lstat
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#undef lstat64
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#undef __lxstat
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#undef __lxstat64
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static int (*real_open)(const char *path, int flags, ...);
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static FILE *(*real_fopen)(const char *path, const char *mode);
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static int (*real_access)(const char *path, int mode);
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static int (*real_stat)(const char *path, struct stat *sb);
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static int (*real_stat64)(const char *path, void *sb);
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static int (*real___xstat)(int ver, const char *path, struct stat *sb);
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static int (*real___xstat64)(int ver, const char *path, void *sb);
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static int (*real_lstat)(const char *path, struct stat *sb);
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static int (*real_lstat64)(const char *path, void *sb);
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static int (*real___lxstat)(int ver, const char *path, struct stat *sb);
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static int (*real___lxstat64)(int ver, const char *path, void *sb);
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static const char *progname;
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const char *output;
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#define VIR_FILE_ACCESS_DEFAULT abs_builddir "/test_file_access.txt"
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static void init_syms(void)
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{
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if (real_open)
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return;
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VIR_MOCK_REAL_INIT(open);
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VIR_MOCK_REAL_INIT(fopen);
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VIR_MOCK_REAL_INIT(access);
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VIR_MOCK_REAL_INIT_ALT(stat, __xstat);
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VIR_MOCK_REAL_INIT_ALT(stat64, __xstat64);
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VIR_MOCK_REAL_INIT_ALT(lstat, __lxstat);
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VIR_MOCK_REAL_INIT_ALT(lstat64, __lxstat64);
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}
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static void
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printFile(const char *file)
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{
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FILE *fp;
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const char *testname = getenv("VIR_TEST_MOCK_TESTNAME");
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if (!progname) {
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progname = getenv("VIR_TEST_MOCK_PROGNAME");
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if (!progname)
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return;
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output = getenv("VIR_TEST_FILE_ACCESS_OUTPUT");
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if (!output)
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output = VIR_FILE_ACCESS_DEFAULT;
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}
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if (!(fp = real_fopen(output, "a"))) {
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fprintf(stderr, "Unable to open %s: %s\n", output, strerror(errno));
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abort();
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}
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if (flock(fileno(fp), LOCK_EX) < 0) {
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fprintf(stderr, "Unable to lock %s: %s\n", output, strerror(errno));
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fclose(fp);
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abort();
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}
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/* Now append the following line into the output file:
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* $file: $progname $testname */
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fprintf(fp, "%s: %s", file, progname);
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if (testname)
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fprintf(fp, ": %s", testname);
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fputc('\n', fp);
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flock(fileno(fp), LOCK_UN);
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fclose(fp);
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}
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static void
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checkPath(const char *path)
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{
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char *fullPath = NULL;
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char *relPath = NULL;
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char *crippledPath = NULL;
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if (path[0] != '/' &&
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virAsprintfQuiet(&relPath, "./%s", path) < 0)
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goto error;
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/* Le sigh. Both canonicalize_file_name() and realpath()
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* expect @path to exist otherwise they return an error. So
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* if we are called over an non-existent file, this could
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* return an error. In that case do our best and hope we will
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* catch possible error. */
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if ((fullPath = canonicalize_file_name(relPath ? relPath : path))) {
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path = fullPath;
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} else {
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/* Yeah, our worst nightmares just became true. Path does
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* not exist. Cut off the last component and retry. */
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if (VIR_STRDUP_QUIET(crippledPath, relPath ? relPath : path) < 0)
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goto error;
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virFileRemoveLastComponent(crippledPath);
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if ((fullPath = canonicalize_file_name(crippledPath)))
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path = fullPath;
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}
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if (!STRPREFIX(path, abs_topsrcdir) &&
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!STRPREFIX(path, abs_topbuilddir)) {
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printFile(path);
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}
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VIR_FREE(crippledPath);
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VIR_FREE(relPath);
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VIR_FREE(fullPath);
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return;
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error:
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fprintf(stderr, "Out of memory\n");
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abort();
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}
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int open(const char *path, int flags, ...)
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{
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int ret;
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init_syms();
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checkPath(path);
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if (flags & O_CREAT) {
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va_list ap;
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mode_t mode;
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va_start(ap, flags);
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mode = va_arg(ap, mode_t);
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va_end(ap);
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ret = real_open(path, flags, mode);
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} else {
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ret = real_open(path, flags);
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}
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return ret;
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}
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FILE *fopen(const char *path, const char *mode)
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{
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init_syms();
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checkPath(path);
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return real_fopen(path, mode);
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}
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int access(const char *path, int mode)
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{
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init_syms();
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checkPath(path);
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return real_access(path, mode);
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}
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/* Okay, the following ifdef rain forest may look messy at a
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* first glance. But here's the thing: during run time linking of
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* a binary, stat() may not be acutally needing symbol stat. It
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* might as well not had been stat() in the first place (see the
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* reasoning at the beginning of this file). However, if we would
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* expose stat symbol here, we will poison the well and trick
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* dynamic linker into thinking we are some old binary that still
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* uses the symbol. So whenever code from upper layers calls
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* stat(), the control would get here, but real_stat can actually
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* be a NULL pointer because newer glibc have __xstat instead.
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* Worse, it can have __xstat64 instead __xstat.
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*
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* Anyway, these ifdefs are there to implement the following
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* preference function:
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*
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* stat < stat64 < __xstat < __xstat64
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*
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* It's the same story with lstat.
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* Also, I feel sorry for you that you had to read this.
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*/
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#if defined(HAVE_STAT) && !defined(HAVE___XSTAT)
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int stat(const char *path, struct stat *sb)
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{
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init_syms();
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checkPath(path);
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return real_stat(path, sb);
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}
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#endif
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#if defined(HAVE_STAT64) && !defined(HAVE___XSTAT64)
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int stat64(const char *path, struct stat64 *sb)
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{
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init_syms();
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checkPath(path);
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return real_stat64(path, sb);
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}
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#endif
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#if defined(HAVE___XSTAT) && !defined(HAVE___XSTAT64)
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int
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__xstat(int ver, const char *path, struct stat *sb)
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{
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init_syms();
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checkPath(path);
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return real___xstat(ver, path, sb);
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}
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#endif
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#if defined(HAVE___XSTAT64)
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int
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__xstat64(int ver, const char *path, struct stat64 *sb)
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{
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init_syms();
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checkPath(path);
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return real___xstat64(ver, path, sb);
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}
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#endif
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#if defined(HAVE_LSTAT) && !defined(HAVE___LXSTAT)
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int
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lstat(const char *path, struct stat *sb)
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{
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init_syms();
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checkPath(path);
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return real_lstat(path, sb);
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}
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#endif
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#if defined(HAVE_LSTAT64) && !defined(HAVE___LXSTAT64)
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int
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lstat64(const char *path, struct stat64 *sb)
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{
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init_syms();
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checkPath(path);
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return real_lstat64(path, sb);
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}
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#endif
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#if defined(HAVE___LXSTAT) && !defined(HAVE___LXSTAT64)
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int
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__lxstat(int ver, const char *path, struct stat *sb)
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{
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init_syms();
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checkPath(path);
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return real___lxstat(ver, path, sb);
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}
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#endif
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#if defined(HAVE___LXSTAT64)
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int
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__lxstat64(int ver, const char *path, struct stat64 *sb)
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{
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init_syms();
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checkPath(path);
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return real___lxstat64(ver, path, sb);
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}
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#endif
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