libgo: Use MAP_FIXED if necessary to grab arena.

From Rainer Orth.

	PR go/48240
	* configure.ac: Check for mincore.
	* configure: Regenerate.
	* config.h.in: Regenerate.
	* runtime/mem.c: Include unistd.h.
	(addrspace_free): New function.
	(runtime_SysMap): Retry 64-bit runtime_mmap with MAP_FIXED.

From-SVN: r171961

libgo/config.h.in

@@ -15,6 +15,9 @@
 /* Define to 1 if you have the <memory.h> header file. */
 #undef HAVE_MEMORY_H
 
+/* Define to 1 if you have the `mincore' function. */
+#undef HAVE_MINCORE
+
 /* Define to 1 if the system has the type `off64_t'. */
 #undef HAVE_OFF64_T
 
@@ -30,6 +33,9 @@
 /* Define to 1 if you have the <stdlib.h> header file. */
 #undef HAVE_STDLIB_H
 
+/* Define to 1 if you have the `strerror_r' function. */
+#undef HAVE_STRERROR_R
+
 /* Define to 1 if you have the <strings.h> header file. */
 #undef HAVE_STRINGS_H
 
@@ -59,6 +65,9 @@
 /* Define to 1 if you have the <sys/ptrace.h> header file. */
 #undef HAVE_SYS_PTRACE_H
 
+/* Define to 1 if you have the <sys/select.h> header file. */
+#undef HAVE_SYS_SELECT_H
+
 /* Define to 1 if you have the <sys/stat.h> header file. */
 #undef HAVE_SYS_STAT_H
 
@@ -77,6 +86,9 @@
 /* Define to 1 if you have the <unistd.h> header file. */
 #undef HAVE_UNISTD_H
 
+/* Define to 1 if you have the `wait4' function. */
+#undef HAVE_WAIT4
+
 /* Define if the C++ compiler is configured for setjmp/longjmp exceptions. */
 #undef LIBGO_SJLJ_EXCEPTIONS
 

libgo/configure

@@ -14266,7 +14266,7 @@ else
 fi
 
 
-for ac_func in srandom random strerror_r strsignal wait4
+for ac_func in srandom random strerror_r strsignal wait4 mincore
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

libgo/configure.ac

@@ -426,7 +426,7 @@ esac
 AC_CHECK_HEADERS(sys/mman.h syscall.h sys/epoll.h sys/ptrace.h sys/syscall.h sys/user.h sys/utsname.h sys/select.h)
 AM_CONDITIONAL(HAVE_SYS_MMAN_H, test "$ac_cv_header_sys_mman_h" = yes)
 
-AC_CHECK_FUNCS(srandom random strerror_r strsignal wait4)
+AC_CHECK_FUNCS(srandom random strerror_r strsignal wait4 mincore)
 AM_CONDITIONAL(HAVE_STRERROR_R, test "$ac_cv_func_strerror_r" = yes)
 AM_CONDITIONAL(HAVE_WAIT4, test "$ac_cv_func_wait4" = yes)
 

libgo/runtime/mem.c

@@ -1,4 +1,5 @@
 #include <errno.h>
+#include <unistd.h>
 
 #include "runtime.h"
 #include "malloc.h"
@@ -16,6 +17,23 @@
 static int dev_zero = -1;
 #endif
 
+static _Bool
+addrspace_free(void *v __attribute__ ((unused)), uintptr n __attribute__ ((unused)))
+{
+#ifdef HAVE_MINCORE
+	size_t page_size = getpagesize();
+	size_t off;
+	char one_byte;
+
+	errno = 0;
+	for(off = 0; off < n; off += page_size)
+		if(mincore((char *)v + off, page_size, (void *)&one_byte) != -1
+		   || errno != ENOMEM)
+			return 0;
+#endif
+	return 1;
+}
+
 void*
 runtime_SysAlloc(uintptr n)
 {
@@ -109,6 +127,11 @@ runtime_SysMap(void *v, uintptr n)
 	// On 64-bit, we don't actually have v reserved, so tread carefully.
 	if(sizeof(void*) == 8) {
 		p = runtime_mmap(v, n, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_ANON|MAP_PRIVATE, fd, 0);
+		if(p != v && addrspace_free(v, n)) {
+			// On some systems, mmap ignores v without
+			// MAP_FIXED, so retry if the address space is free.
+			p = runtime_mmap(v, n, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_ANON|MAP_FIXED|MAP_PRIVATE, fd, 0);
+		}
 		if(p != v) {
 			runtime_printf("runtime: address space conflict: map(%p) = %p\n", v, p);
 			runtime_throw("runtime: address space conflict");