runtime: add mmap of null page just in case

R=r, iant, robert.swiecki, rsc1
CC=golang-dev
https://golang.org/cl/1904044

src/pkg/runtime/darwin/386/defs.h

@@ -10,6 +10,7 @@ enum {
 	PROT_EXEC = 0x4,
 	MAP_ANON = 0x1000,
 	MAP_PRIVATE = 0x2,
+	MAP_FIXED = 0x10,
 	MACH_MSG_TYPE_MOVE_RECEIVE = 0x10,
 	MACH_MSG_TYPE_MOVE_SEND = 0x11,
 	MACH_MSG_TYPE_MOVE_SEND_ONCE = 0x12,

src/pkg/runtime/darwin/386/sys.s

@@ -38,8 +38,6 @@ TEXT write(SB),7,$0
 TEXT ·mmap(SB),7,$0
 	MOVL	$197, AX
 	INT	$0x80
-	JAE	2(PC)
-	CALL	notok(SB)
 	RET
 
 TEXT ·munmap(SB),7,$0

src/pkg/runtime/darwin/amd64/defs.h

@@ -10,6 +10,7 @@ enum {
 	PROT_EXEC = 0x4,
 	MAP_ANON = 0x1000,
 	MAP_PRIVATE = 0x2,
+	MAP_FIXED = 0x10,
 	MACH_MSG_TYPE_MOVE_RECEIVE = 0x10,
 	MACH_MSG_TYPE_MOVE_SEND = 0x11,
 	MACH_MSG_TYPE_MOVE_SEND_ONCE = 0x12,

src/pkg/runtime/darwin/amd64/sys.s

@@ -103,8 +103,6 @@ TEXT	·mmap(SB),7,$0
 	MOVL	36(SP), R9		// arg 6 offset
 	MOVL	$(0x2000000+197), AX	// syscall entry
 	SYSCALL
-	JCC	2(PC)
-	CALL	notok(SB)
 	RET
 
 TEXT ·munmap(SB),7,$0

src/pkg/runtime/darwin/defs.c

@@ -26,6 +26,7 @@ enum {
 
 	$MAP_ANON = MAP_ANON,
 	$MAP_PRIVATE = MAP_PRIVATE,
+	$MAP_FIXED = MAP_FIXED,
 
 	$MACH_MSG_TYPE_MOVE_RECEIVE = MACH_MSG_TYPE_MOVE_RECEIVE,
 	$MACH_MSG_TYPE_MOVE_SEND = MACH_MSG_TYPE_MOVE_SEND,

src/pkg/runtime/darwin/mem.c

@@ -6,8 +6,15 @@
 void*
 SysAlloc(uintptr n)
 {
+	void *v;
+
 	mstats.sys += n;
-	return runtime_mmap(nil, n, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_ANON|MAP_PRIVATE, -1, 0);
+	v = runtime_mmap(nil, n, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_ANON|MAP_PRIVATE, -1, 0);
+	if(v < (void*)4096) {
+		printf("mmap: errno=%p\n", v);
+		throw("mmap");
+	}
+	return v;
 }
 
 void
@@ -25,3 +32,15 @@ SysFree(void *v, uintptr n)
 	runtime_munmap(v, n);
 }
 
+
+void
+SysMemInit(void)
+{
+	// Code generators assume that references to addresses
+	// on the first page will fault.  Map the page explicitly with
+	// no permissions, to head off possible bugs like the system
+	// allocating that page as the virtual address space fills.
+	// Ignore any error, since other systems might be smart
+	// enough to never allow anything there.
+//	runtime_mmap(nil, 4096, PROT_NONE, MAP_FIXED|MAP_ANON|MAP_PRIVATE, -1, 0);
+}

src/pkg/runtime/freebsd/386/defs.h

@@ -10,6 +10,7 @@ enum {
 	PROT_EXEC = 0x4,
 	MAP_ANON = 0x1000,
 	MAP_PRIVATE = 0x2,
+	MAP_FIXED = 0x10,
 	SA_SIGINFO = 0x40,
 	SA_RESTART = 0x2,
 	SA_ONSTACK = 0x1,

src/pkg/runtime/freebsd/386/sys.s

@@ -80,8 +80,6 @@ TEXT ·mmap(SB),7,$32
 	STOSL
 	MOVL	$477, AX
 	INT	$0x80
-	JAE	2(PC)
-	CALL	notok(SB)
 	RET
 
 TEXT ·munmap(SB),7,$-4

src/pkg/runtime/freebsd/amd64/defs.h

@@ -10,6 +10,7 @@ enum {
 	PROT_EXEC = 0x4,
 	MAP_ANON = 0x1000,
 	MAP_PRIVATE = 0x2,
+	MAP_FIXED = 0x10,
 	SA_SIGINFO = 0x40,
 	SA_RESTART = 0x2,
 	SA_ONSTACK = 0x1,

src/pkg/runtime/freebsd/amd64/sys.s

@@ -112,8 +112,6 @@ TEXT	·mmap(SB),7,$0
 	MOVL	36(SP), R9		// arg 6 offset
 	MOVL	$477, AX
 	SYSCALL
-	JCC	2(PC)
-	CALL	notok(SB)
 	RET
 
 TEXT	·munmap(SB),7,$0

src/pkg/runtime/freebsd/defs.c

@@ -28,6 +28,7 @@ enum {
 
 	$MAP_ANON = MAP_ANON,
 	$MAP_PRIVATE = MAP_PRIVATE,
+	$MAP_FIXED = MAP_FIXED,
 
 	$SA_SIGINFO = SA_SIGINFO,
 	$SA_RESTART = SA_RESTART,

src/pkg/runtime/freebsd/mem.c

@@ -6,8 +6,15 @@
 void*
 SysAlloc(uintptr n)
 {
+	void *v;
+
 	mstats.sys += n;
-	return runtime_mmap(nil, n, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_ANON|MAP_PRIVATE, -1, 0);
+	v = runtime_mmap(nil, n, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_ANON|MAP_PRIVATE, -1, 0);
+	if(v < (void*)4096) {
+		printf("mmap: errno=%p\n", p);
+		throw("mmap");
+	}
+	return v;
 }
 
 void
@@ -25,3 +32,15 @@ SysFree(void *v, uintptr n)
 	runtime_munmap(v, n);
 }
 
+
+void
+SysMemInit(void)
+{
+	// Code generators assume that references to addresses
+	// on the first page will fault.  Map the page explicitly with
+	// no permissions, to head off possible bugs like the system
+	// allocating that page as the virtual address space fills.
+	// Ignore any error, since other systems might be smart
+	// enough to never allow anything there.
+	runtime_mmap(nil, 4096, PROT_NONE, MAP_FIXED|MAP_ANON|MAP_PRIVATE, -1, 0);
+}

src/pkg/runtime/linux/386/defs.h

@@ -10,6 +10,7 @@ enum {
 	PROT_EXEC = 0x4,
 	MAP_ANON = 0x20,
 	MAP_PRIVATE = 0x2,
+	MAP_FIXED = 0x10,
 	SA_RESTART = 0x10000000,
 	SA_ONSTACK = 0x8000000,
 	SA_RESTORER = 0x4000000,

src/pkg/runtime/linux/amd64/defs.h

@@ -10,6 +10,7 @@ enum {
 	PROT_EXEC = 0x4,
 	MAP_ANON = 0x20,
 	MAP_PRIVATE = 0x2,
+	MAP_FIXED = 0x10,
 	SA_RESTART = 0x10000000,
 	SA_ONSTACK = 0x8000000,
 	SA_RESTORER = 0x4000000,

src/pkg/runtime/linux/arm/defs.h

@@ -10,6 +10,7 @@ enum {
 	PROT_EXEC = 0x4,
 	MAP_ANON = 0x20,
 	MAP_PRIVATE = 0x2,
+	MAP_FIXED = 0x10,
 	SA_RESTART = 0x10000000,
 	SA_ONSTACK = 0x8000000,
 	SA_RESTORER = 0x4000000,

src/pkg/runtime/linux/defs.c

@@ -27,6 +27,7 @@ enum {
 
 	$MAP_ANON = MAP_ANONYMOUS,
 	$MAP_PRIVATE = MAP_PRIVATE,
+	$MAP_FIXED = MAP_FIXED,
 
 	$SA_RESTART = SA_RESTART,
 	$SA_ONSTACK = SA_ONSTACK,

src/pkg/runtime/linux/defs2.c

@@ -47,6 +47,7 @@ enum {
 
 	$MAP_ANON = MAP_ANONYMOUS,
 	$MAP_PRIVATE = MAP_PRIVATE,
+	$MAP_FIXED = MAP_FIXED,
 
 	$SA_RESTART = SA_RESTART,
 	$SA_ONSTACK = SA_ONSTACK,

src/pkg/runtime/linux/defs_arm.c

@@ -31,6 +31,7 @@ enum {
 
 	$MAP_ANON = MAP_ANONYMOUS,
 	$MAP_PRIVATE = MAP_PRIVATE,
+	$MAP_FIXED = MAP_FIXED,
 
 	$SA_RESTART = SA_RESTART,
 	$SA_ONSTACK = SA_ONSTACK,

src/pkg/runtime/linux/mem.c

@@ -14,10 +14,10 @@ SysAlloc(uintptr n)
 		if(p == (void*)EACCES) {
 			printf("mmap: access denied\n");
 			printf("If you're running SELinux, enable execmem for this process.\n");
-		} else {
-			printf("mmap: errno=%p\n", p);
+			exit(2);
 		}
-		exit(2);
+		printf("mmap: errno=%p\n", p);
+		throw("mmap");
 	}
 	return p;
 }
@@ -37,3 +37,14 @@ SysFree(void *v, uintptr n)
 	runtime_munmap(v, n);
 }
 
+void
+SysMemInit(void)
+{
+	// Code generators assume that references to addresses
+	// on the first page will fault.  Map the page explicitly with
+	// no permissions, to head off possible bugs like the system
+	// allocating that page as the virtual address space fills.
+	// Ignore any error, since other systems might be smart
+	// enough to never allow anything there.
+	runtime_mmap(nil, 4096, PROT_NONE, MAP_FIXED|MAP_ANON|MAP_PRIVATE, -1, 0);
+}

src/pkg/runtime/malloc.goc

@@ -245,6 +245,7 @@ allocmcache(void)
 void
 mallocinit(void)
 {
+	SysMemInit();
 	InitSizes();
 	MHeap_Init(&mheap, SysAlloc);
 	m->mcache = allocmcache();

src/pkg/runtime/malloc.h

@@ -138,7 +138,7 @@ struct MLink
 void*	SysAlloc(uintptr nbytes);
 void	SysFree(void *v, uintptr nbytes);
 void	SysUnused(void *v, uintptr nbytes);
-
+void	SysMemInit(void);
 
 // FixAlloc is a simple free-list allocator for fixed size objects.
 // Malloc uses a FixAlloc wrapped around SysAlloc to manages its

src/pkg/runtime/nacl/mem.c

@@ -31,3 +31,7 @@ SysFree(void *v, uintptr n)
 	runtime_munmap(v, n);
 }
 
+void
+SysMemInit(void)
+{
+}

src/pkg/runtime/tiny/mem.c

@@ -44,3 +44,7 @@ SysUnused(void *v, uintptr n)
 	USED(v, n);
 }
 
+void
+SysMemInit(void)
+{
+}

src/pkg/runtime/windows/mem.c

@@ -33,3 +33,8 @@ SysFree(void *v, uintptr n)
 {
 	stdcall(VirtualFree, 3, v, n, MEM_RELEASE);
 }
+
+void
+SysMemInit(void)
+{
+}