I'm adding a unit test for the "free() preserves errno" feature.
The idea for the Linux specific test is from
<https://sourceware.org/legacy-ml/libc-alpha/2015-02/msg00067.html>
where Rich Felker wrote:
free can make a syscall that will set errno unless you suppress this
behavior -- munmap can fail due to inability to split an existing vma
due to hitting the vma limit or simply a kernel oom condition.
2020-12-19 Bruno Haible <br...@clisp.org>
free-posix: Add tests.
* tests/test-free.c: New file.
* tests/macros.h (ASSERT_NO_STDIO,
WRITE_MACROEXPANDED_INTEGER_TO_STDERR, WRITE_INTEGER_TO_STDERR,
WRITE_TO_STDERR): New macros.
* modules/free-posix-tests: New file.
diff --git a/tests/test-free.c b/tests/test-free.c
new file mode 100644
index 0000000..4fa1d3a
--- /dev/null
+++ b/tests/test-free.c
@@ -0,0 +1,173 @@
+/* Test of free() function.
+ Copyright (C) 2020 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>. */
+
+/* Written by Bruno Haible <br...@clisp.org>, 2020. */
+
+#include <config.h>
+
+/* Specification. */
+#include <stdlib.h>
+
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+#if defined __linux__
+# include <fcntl.h>
+# include <stdint.h>
+# include <string.h>
+# include <sys/mman.h>
+#endif
+
+#include "macros.h"
+
+/* The indirection through a volatile function pointer is necessary to prevent
+ a GCC optimization. Without it, when optimizing, GCC would "know" that
errno
+ is unchanged by calling free(ptr), when ptr was the result of a malloc(...)
+ call in the same function. */
+static int
+get_errno (void)
+{
+ volatile int err = errno;
+ return err;
+}
+
+static int (* volatile get_errno_func) (void) = get_errno;
+
+int
+main ()
+{
+ /* Check that free() preserves errno. */
+ {
+ errno = 1789; /* Liberté, égalité, fraternité. */
+ free (NULL);
+ ASSERT_NO_STDIO (get_errno_func () == 1789);
+ }
+ { /* Small memory allocations. */
+ #define N 10000
+ void * volatile ptrs[N];
+ size_t i;
+ for (i = 0; i < N; i++)
+ ptrs[i] = malloc (15);
+ for (i = 0; i < N; i++)
+ {
+ errno = 1789;
+ free (ptrs[i]);
+ ASSERT_NO_STDIO (get_errno_func () == 1789);
+ }
+ #undef N
+ }
+ { /* Medium memory allocations. */
+ #define N 1000
+ void * volatile ptrs[N];
+ size_t i;
+ for (i = 0; i < N; i++)
+ ptrs[i] = malloc (729);
+ for (i = 0; i < N; i++)
+ {
+ errno = 1789;
+ free (ptrs[i]);
+ ASSERT_NO_STDIO (get_errno_func () == 1789);
+ }
+ #undef N
+ }
+ { /* Large memory allocations. */
+ #define N 10
+ void * volatile ptrs[N];
+ size_t i;
+ for (i = 0; i < N; i++)
+ ptrs[i] = malloc (5318153);
+ for (i = 0; i < N; i++)
+ {
+ errno = 1789;
+ free (ptrs[i]);
+ ASSERT_NO_STDIO (get_errno_func () == 1789);
+ }
+ #undef N
+ }
+
+ /* Test a less common code path.
+ When malloc() is based on mmap(), free() can sometimes call munmap().
+ munmap() usually succeeds, but fails in a particular situation: when
+ - it has to unmap the middle part of a VMA, and
+ - the number of VMAs of a process is limited and the limit is
+ already reached.
+ The latter condition is fulfilled on Linux, when the file
+ /proc/sys/vm/max_map_count exists. This file contains the limit
+ - for Linux >= 2.4.19: 65536 (DEFAULT_MAX_MAP_COUNT in
linux/include/linux/sched.h)
+ - for Linux >= 2.6.31: 65530 (DEFAULT_MAX_MAP_COUNT in
linux/include/linux/mm.h).
+ */
+ #if defined __linux__
+ if (open ("/proc/sys/vm/max_map_count", O_RDONLY) >= 0)
+ {
+ /* Preparations. */
+ size_t pagesize = getpagesize ();
+ void *firstpage_backup = malloc (pagesize);
+ void *lastpage_backup = malloc (pagesize);
+ /* Allocate a large memory area, as a bumper, so that the MAP_FIXED
+ allocation later will not overwrite parts of the memory areas
+ allocated to ld.so or libc.so. */
+ void *bumper_region =
+ mmap (NULL, 0x1000000, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+ /* A file descriptor pointing to a regular file. */
+ int fd = open ("test-free", O_RDONLY);
+
+ if (firstpage_backup != NULL && lastpage_backup != NULL
+ && bumper_region != (void *)(-1)
+ && fd >= 0)
+ {
+ /* Do a large memory allocation. */
+ size_t big_size = 0x1000000;
+ void * volatile ptr = malloc (big_size - 0x100);
+ char *ptr_aligned = (char *) ((uintptr_t) ptr & ~(pagesize - 1));
+ /* This large memory allocation allocated a memory area
+ from ptr_aligned to ptr_aligned + big_size.
+ Enlarge this memory area by adding a page before and a page
+ after it. */
+ memcpy (firstpage_backup, ptr_aligned, pagesize);
+ memcpy (lastpage_backup, ptr_aligned + big_size - pagesize,
pagesize);
+ if (mmap (ptr_aligned - pagesize, pagesize + big_size + pagesize,
+ PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0)
+ != (void *)(-1))
+ {
+ memcpy (ptr_aligned, firstpage_backup, pagesize);
+ memcpy (ptr_aligned + big_size - pagesize, lastpage_backup,
pagesize);
+
+ /* Now add as many mappings as we can.
+ Stop at 65536, in order not to crash the machine (in case the
+ limit has been increased by the system administrator). */
+ size_t i;
+ for (i = 0; i < 65536; i++)
+ if (mmap (NULL, pagesize, PROT_READ, MAP_FILE | MAP_PRIVATE,
fd, 0)
+ == (void *)(-1))
+ break;
+ /* Now the number of VMAs of this process has hopefully attained
+ its limit. */
+
+ errno = 1789;
+ /* This call to free() is supposed to call
+ munmap (ptr_aligned, big_size);
+ which increases the number of VMAs by 1, which is supposed
+ to fail. */
+ free (ptr);
+ ASSERT_NO_STDIO (get_errno_func () == 1789);
+ }
+ }
+ }
+ #endif
+
+ return 0;
+}
diff --git a/modules/free-posix-tests b/modules/free-posix-tests
new file mode 100644
index 0000000..8e81c22
--- /dev/null
+++ b/modules/free-posix-tests
@@ -0,0 +1,12 @@
+Files:
+tests/test-free.c
+tests/macros.h
+
+Depends-on:
+unistd
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-free
+check_PROGRAMS += test-free
diff --git a/tests/macros.h b/tests/macros.h
index bbc340d..3fd816b 100644
--- a/tests/macros.h
+++ b/tests/macros.h
@@ -56,14 +56,42 @@
{ \
if (!(expr)) \
{ \
- fprintf (ASSERT_STREAM, "%s:%d: assertion '%s' failed\n", \
- __FILE__, __LINE__, #expr); \
+ fprintf (ASSERT_STREAM, "%s:%d: assertion '%s' failed\n", \
+ __FILE__, __LINE__, #expr); \
fflush (ASSERT_STREAM); \
abort (); \
} \
} \
while (0)
+/* Like ASSERT, except that it uses no stdio.
+ Requires #include <string.h> and #include <unistd.h>. */
+#define ASSERT_NO_STDIO(expr) \
+ do \
+ { \
+ if (!(expr)) \
+ { \
+ WRITE_TO_STDERR (__FILE__); \
+ WRITE_TO_STDERR (":"); \
+ WRITE_MACROEXPANDED_INTEGER_TO_STDERR (__LINE__); \
+ WRITE_TO_STDERR (": assertion '"); \
+ WRITE_TO_STDERR (#expr); \
+ WRITE_TO_STDERR ("' failed\n"); \
+ abort (); \
+ } \
+ } \
+ while (0)
+#define WRITE_MACROEXPANDED_INTEGER_TO_STDERR(integer) \
+ WRITE_INTEGER_TO_STDERR(integer)
+#define WRITE_INTEGER_TO_STDERR(integer) \
+ WRITE_TO_STDERR (#integer)
+#define WRITE_TO_STDERR(string_literal) \
+ { \
+ const char *s = string_literal; \
+ int ret = write (2, s, strlen (s)); \
+ (void) ret; \
+ }
+
/* SIZEOF (array)
returns the number of elements of an array. It works for arrays that are
declared outside functions and for local variables of array type. It does
