runtime: linux signal masking

Fixes #3101 (Linux).

R=golang-dev, bradfitz, minux.ma
CC=golang-dev
https://golang.org/cl/5696043

src/pkg/runtime/os_linux.h

@@ -22,3 +22,14 @@ void	runtime·raisesigpipe(void);
 
 #define	NSIG	65
 #define	SI_USER 0
+
+// It's hard to tease out exactly how big a Sigset is, but
+// rt_sigprocmask crashes if we get it wrong, so if binaries
+// are running, this is right.
+typedef struct Sigset Sigset;
+struct Sigset
+{
+	uint32 mask[2];
+};
+void	runtime·rtsigprocmask(int32, Sigset*, Sigset*, int32);
+#define SIG_SETMASK 2

src/pkg/runtime/sys_linux_386.s

@@ -136,6 +136,18 @@ TEXT runtime·nanotime(SB), 7, $32
 	MOVL	DX, 4(DI)
 	RET
 
+TEXT runtime·rtsigprocmask(SB),7,$0
+	MOVL	$175, AX		// syscall entry
+	MOVL	4(SP), BX
+	MOVL	8(SP), CX
+	MOVL	12(SP), DX
+	MOVL	16(SP), SI
+	CALL	*runtime·_vdso(SB)
+	CMPL	AX, $0xfffff001
+	JLS	2(PC)
+	INT $3
+	RET
+
 TEXT runtime·rt_sigaction(SB),7,$0
 	MOVL	$174, AX		// syscall - rt_sigaction
 	MOVL	4(SP), BX

src/pkg/runtime/sys_linux_amd64.s

@@ -123,6 +123,18 @@ TEXT runtime·nanotime(SB), 7, $32
 	ADDQ	DX, AX
 	RET
 
+TEXT runtime·rtsigprocmask(SB),7,$0-32
+	MOVL	8(SP), DI
+	MOVQ	16(SP), SI
+	MOVQ	24(SP), DX
+	MOVL	32(SP), R10
+	MOVL	$14, AX			// syscall entry
+	SYSCALL
+	CMPQ	AX, $0xfffffffffffff001
+	JLS	2(PC)
+	CALL	runtime·notok(SB)
+	RET
+
 TEXT runtime·rt_sigaction(SB),7,$0-32
 	MOVL	8(SP), DI
 	MOVQ	16(SP), SI

src/pkg/runtime/sys_linux_arm.s

@@ -23,6 +23,7 @@
 #define SYS_clone (SYS_BASE + 120)
 #define SYS_rt_sigreturn (SYS_BASE + 173)
 #define SYS_rt_sigaction (SYS_BASE + 174)
+#define SYS_rt_sigprocmask (SYS_BASE + 175)
 #define SYS_sigaltstack (SYS_BASE + 186)
 #define SYS_mmap2 (SYS_BASE + 192)
 #define SYS_futex (SYS_BASE + 240)
@@ -292,6 +293,15 @@ TEXT runtime·sigtramp(SB),7,$24
 
 	RET
 
+TEXT runtime·rtsigprocmask(SB),7,$0
+	MOVW	0(FP), R0
+	MOVW	4(FP), R1
+	MOVW	8(FP), R2
+	MOVW	12(FP), R3
+	MOVW	$SYS_rt_sigprocmask, R7
+	SWI	$0
+	RET
+
 TEXT runtime·rt_sigaction(SB),7,$0
 	MOVW	0(FP), R0
 	MOVW	4(FP), R1

src/pkg/runtime/thread_linux.c

@@ -13,6 +13,9 @@ int32 runtime·open(uint8*, int32, int32);
 int32 runtime·close(int32);
 int32 runtime·read(int32, void*, int32);
 
+static Sigset sigset_all = { ~(uint32)0, ~(uint32)0 };
+static Sigset sigset_none;
+
 // Linux futex.
 //
 //	futexsleep(uint32 *addr, uint32 val)
@@ -135,6 +138,7 @@ runtime·newosproc(M *m, G *g, void *stk, void (*fn)(void))
 {
 	int32 ret;
 	int32 flags;
+	Sigset oset;
 
 	/*
 	 * note: strace gets confused if we use CLONE_PTRACE here.
@@ -152,7 +156,13 @@ runtime·newosproc(M *m, G *g, void *stk, void (*fn)(void))
 			stk, m, g, fn, runtime·clone, m->id, m->tls[0], &m);
 	}
 
-	if((ret = runtime·clone(flags, stk, m, g, fn)) < 0) {
+	// Disable signals during clone, so that the new thread starts
+	// with signals disabled.  It will enable them in minit.
+	runtime·rtsigprocmask(SIG_SETMASK, &sigset_all, &oset, sizeof oset);
+	ret = runtime·clone(flags, stk, m, g, fn);
+	runtime·rtsigprocmask(SIG_SETMASK, &oset, nil, sizeof oset);
+
+	if(ret < 0) {
 		runtime·printf("runtime: failed to create new OS thread (have %d already; errno=%d)\n", runtime·mcount(), -ret);
 		runtime·throw("runtime.newosproc");
 	}
@@ -177,6 +187,7 @@ runtime·minit(void)
 	// Initialize signal handling.
 	m->gsignal = runtime·malg(32*1024);	// OS X wants >=8K, Linux >=2K
 	runtime·signalstack(m->gsignal->stackguard - StackGuard, 32*1024);
+	runtime·rtsigprocmask(SIG_SETMASK, &sigset_none, nil, sizeof sigset_none);
 }
 
 void