libgcc: use syscall rather than __mmap/__munmap

	PR libgcc/94513
	* generic-morestack.c: Give up trying to use __mmap/__munmap, use
	syscall instead.

libgcc/ChangeLog

+2020-04-07  Ian Lance Taylor  <iant@golang.org>
+
+	PR libgcc/94513
+	* generic-morestack.c: Give up trying to use __mmap/__munmap, use
+	syscall instead.
+
 2020-04-04  Ian Lance Taylor  <iant@golang.org>
 
 	* generic-morestack.c: Only use __mmap on glibc >= 2.26.

libgcc/generic-morestack.c

@@ -56,17 +56,56 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 /* Some systems use LD_PRELOAD or similar tricks to add hooks to
    mmap/munmap.  That breaks this code, because when we call mmap
    there is enough stack space for the system call but there is not,
-   in general, enough stack space to run a hook.  At least when using
-   glibc on GNU/Linux we can avoid the problem by calling __mmap and
-   __munmap.  */
+   in general, enough stack space to run a hook.  Try to avoid the
+   problem by calling syscall directly.  We only do this on GNU/Linux
+   for now, but it should be easy to add support for more systems with
+   testing.  */
 
-#if defined(__gnu_linux__) && (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 26))
+#if defined(__gnu_linux__)
 
-extern void *__mmap (void *, size_t, int, int, int, off_t);
-extern int __munmap (void *, size_t);
+#include <sys/syscall.h>
 
-#define mmap __mmap
-#define munmap __munmap
+#if defined(SYS_mmap) || defined(SYS_mmap2)
+
+#ifdef SYS_mmap2
+#define MORESTACK_MMAP SYS_mmap2
+#define MORESTACK_ADJUST_OFFSET(x) ((x) / 4096ULL)
+#else
+#define MORESTACK_MMAP SYS_mmap
+#define MORESTACK_ADJUST_OFFSET(x) (x)
+#endif
+
+static void *
+morestack_mmap (void *addr, size_t length, int prot, int flags, int fd,
+		off_t offset)
+{
+  offset = MORESTACK_ADJUST_OFFSET (offset);
+
+#ifdef __s390__
+  long args[6] = { (long) addr, (long) length, (long) prot, (long) flags,
+		   (long) fd, (long) offset };
+  return (void *) syscall (MORESTACK_MMAP, args);
+#else
+  return (void *) syscall (MORESTACK_MMAP, addr, length, prot, flags, fd,
+			   offset);
+#endif
+}
+
+#define mmap morestack_mmap
+
+#endif /* defined(SYS_MMAP) || defined(SYS_mmap2) */
+
+#if defined(SYS_munmap)
+
+static int
+morestack_munmap (void * addr, size_t length)
+{
+  return (int) syscall (SYS_munmap, addr, length);
+}
+
+#define munmap morestack_munmap
+
+#endif /* defined(SYS_munmap) */
 
 #endif /* defined(__gnu_linux__) */