gdb/testsuite: check mmap ret val against MAP_FAILED

Fixup a few spots in the testsuite that use mmap to consistently check
the return value against MAP_FAILED.

One spot in gdb.base/coredump-filter.c checked against NULL, that is
wrong.  The other spots either didn't check, or checked against -1.
MAP_FAILED has the value -1, at least on Linux, but it's better to check
against the documented define.

gdb/testsuite/ChangeLog:

	PR gdb/26016
	* gdb.base/coredump-filter.c (do_mmap): Check mmap ret val
	against MAP_FAILED.
	* gdb.base/coremaker.c (mmapdata): Likewise.
	* gdb.base/jit-reader-host.c (main): Likewise.
	* gdb.base/sym-file-loader.c (load): Likewise.
	(load_shlib): Likewise.

gdb/testsuite/ChangeLog

@@ -1,3 +1,13 @@
+2020-05-20  Simon Marchi  <simon.marchi@efficios.com>
+
+	PR gdb/26016
+	* gdb.base/coredump-filter.c (do_mmap): Check mmap ret val
+	against MAP_FAILED.
+	* gdb.base/coremaker.c (mmapdata): Likewise.
+	* gdb.base/jit-reader-host.c (main): Likewise.
+	* gdb.base/sym-file-loader.c (load): Likewise.
+	(load_shlib): Likewise.
+
 2020-05-20  Tom Tromey  <tromey@adacore.com>
 
 	* gdb.ada/array_char_idx.exp: Recognize initialized array.

gdb/testsuite/gdb.base/coredump-filter.c

@@ -29,7 +29,7 @@ do_mmap (void *addr, size_t size, int prot, int flags, int fd, off_t offset)
 {
   void *ret = mmap (addr, size, prot, flags, fd, offset);
 
-  assert (ret != NULL);
+  assert (ret != MAP_FAILED);
   return ret;
 }
 

gdb/testsuite/gdb.base/coremaker.c

@@ -77,7 +77,7 @@ mmapdata ()
   /* Now map the file into our address space as buf2 */
 
   buf2 = (char *) mmap (0, MAPSIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
-  if (buf2 == (char *) -1)
+  if (buf2 == (char *) MAP_FAILED)
     {
       perror ("mmap failed");
       return;

gdb/testsuite/gdb.base/jit-reader-host.c

@@ -15,6 +15,7 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -59,6 +60,8 @@ main (int argc, char **argv)
 		     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
   char *code_end = code;
 
+  assert (code != MAP_FAILED);
+
   /* "JIT" function_stack_mangle.  */
   memcpy (code_end, jit_function_stack_mangle_code,
 	  sizeof (jit_function_stack_mangle_code));

gdb/testsuite/gdb.base/sym-file-loader.c

@@ -20,6 +20,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
+#include <assert.h>
 
 #include "sym-file-loader.h"
 
@@ -112,6 +113,8 @@ load (uint8_t *addr, Elf_External_Phdr *phdr, struct segment *tail_seg)
   mapped_addr = (uint8_t *) mmap ((void *) GETADDR (phdr, p_vaddr),
 				  GET (phdr, p_memsz), perm,
 				  MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+  assert (mapped_addr != MAP_FAILED);
+
   mapped_size = GET (phdr, p_memsz);
 
   from = (void *) (addr + GET (phdr, p_offset));
@@ -255,7 +258,7 @@ load_shlib (const char *file)
     }
 
   addr = (uint8_t *) mmap (NULL, fsize, PROT_READ, MAP_PRIVATE, fd, 0);
-  if (addr == (uint8_t *) -1)
+  if (addr == MAP_FAILED)
     {
       perror ("mmap failed.");
       return NULL;