runtime: unify handling of alternate signal stack

Change all Unix systems to use stackt for the alternate signal
stack (some were using sigaltstackt). Add OS-specific setSignalstackSP
function to handle different types for ss_sp field, and unify all
OS-specific signalstack functions into one. Unify handling of alternate
signal stack in OS-specific minit and sigtrampgo functions via new
functions minitSignalstack and setGsignalStack.

Change-Id: Idc316dc69b1dd725717acdf61a1cd8b9f33ed174
Reviewed-on: https://go-review.googlesource.com/29757
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/defs1_linux.go

@@ -33,7 +33,7 @@ type Fpxreg1 C.struct__fpxreg
 type Xmmreg1 C.struct__xmmreg
 type Fpstate1 C.struct__fpstate
 type Fpreg1 C.struct__fpreg
-type SigaltstackT C.struct_sigaltstack
+type StackT C.stack_t
 type Mcontext C.mcontext_t
 type Ucontext C.ucontext_t
 type Sigcontext C.struct_sigcontext

src/runtime/defs1_netbsd_386.go

@@ -83,12 +83,6 @@ const (
 	_EVFILT_WRITE = 0x1
 )
 
-type sigaltstackt struct {
-	ss_sp    uintptr
-	ss_size  uintptr
-	ss_flags int32
-}
-
 type sigset struct {
 	__bits [4]uint32
 }

src/runtime/defs1_netbsd_amd64.go

@@ -83,13 +83,6 @@ const (
 	_EVFILT_WRITE = 0x1
 )
 
-type sigaltstackt struct {
-	ss_sp     uintptr
-	ss_size   uintptr
-	ss_flags  int32
-	pad_cgo_0 [4]byte
-}
-
 type sigset struct {
 	__bits [4]uint32
 }

src/runtime/defs1_netbsd_arm.go

@@ -83,12 +83,6 @@ const (
 	_EVFILT_WRITE = 0x1
 )
 
-type sigaltstackt struct {
-	ss_sp    uintptr
-	ss_size  uintptr
-	ss_flags int32
-}
-
 type sigset struct {
 	__bits [4]uint32
 }

src/runtime/defs1_solaris_amd64.go

@@ -110,20 +110,13 @@ type semt struct {
 	sem_pad2  [2]uint64
 }
 
-type sigaltstackt struct {
-	ss_sp     *byte
-	ss_size   uint64
-	ss_flags  int32
-	pad_cgo_0 [4]byte
-}
-
 type sigset struct {
 	__sigbits [4]uint32
 }
 
 type stackt struct {
 	ss_sp     *byte
-	ss_size   uint64
+	ss_size   uintptr
 	ss_flags  int32
 	pad_cgo_0 [4]byte
 }

src/runtime/defs2_linux.go

@@ -139,7 +139,7 @@ type Timespec C.struct_timespec
 type Timeval C.struct_timeval
 type Sigaction C.struct_kernel_sigaction
 type Siginfo C.siginfo_t
-type SigaltstackT C.struct_sigaltstack
+type StackT C.stack_t
 type Sigcontext C.struct_sigcontext
 type Ucontext C.struct_ucontext
 type Itimerval C.struct_itimerval

src/runtime/defs3_linux.go

@@ -35,7 +35,7 @@ type Gregset C.elf_gregset_t
 type FPregset C.elf_fpregset_t
 type Vreg C.elf_vrreg_t
 
-type SigaltstackT C.struct_sigaltstack
+type StackT C.stack_t
 
 // PPC64 uses sigcontext in place of mcontext in ucontext.
 // see http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/include/uapi/asm/ucontext.h

src/runtime/defs_arm_linux.go

@@ -115,7 +115,7 @@ const (
 )
 
 type Timespec C.struct_timespec
-type SigaltstackT C.struct_sigaltstack
+type StackT C.stack_t
 type Sigcontext C.struct_sigcontext
 type Ucontext C.struct_ucontext
 type Timeval C.struct_timeval

src/runtime/defs_dragonfly.go

@@ -109,7 +109,6 @@ const (
 
 type Rtprio C.struct_rtprio
 type Lwpparams C.struct_lwp_params
-type SigaltstackT C.struct_sigaltstack
 type Sigset C.struct___sigset
 type StackT C.stack_t
 

src/runtime/defs_dragonfly_amd64.go

@@ -99,13 +99,6 @@ type lwpparams struct {
 	tid2       unsafe.Pointer // *int32
 }
 
-type sigaltstackt struct {
-	ss_sp     uintptr
-	ss_size   uintptr
-	ss_flags  int32
-	pad_cgo_0 [4]byte
-}
-
 type sigset struct {
 	__bits [4]uint32
 }

src/runtime/defs_freebsd.go

@@ -117,7 +117,6 @@ const (
 
 type Rtprio C.struct_rtprio
 type ThrParam C.struct_thr_param
-type SigaltstackT C.struct_sigaltstack
 type Sigset C.struct___sigset
 type StackT C.stack_t
 

src/runtime/defs_freebsd_386.go

@@ -109,12 +109,6 @@ type thrparam struct {
 	spare      [3]uintptr
 }
 
-type sigaltstackt struct {
-	ss_sp    *int8
-	ss_size  uint32
-	ss_flags int32
-}
-
 type sigset struct {
 	__bits [4]uint32
 }

src/runtime/defs_freebsd_amd64.go

@@ -110,13 +110,6 @@ type thrparam struct {
 	spare      [3]uintptr
 }
 
-type sigaltstackt struct {
-	ss_sp     *int8
-	ss_size   uint64
-	ss_flags  int32
-	pad_cgo_0 [4]byte
-}
-
 type sigset struct {
 	__bits [4]uint32
 }

src/runtime/defs_freebsd_arm.go

@@ -109,12 +109,6 @@ type thrparam struct {
 	spare      [3]uintptr
 }
 
-type sigaltstackt struct {
-	ss_sp    *uint8
-	ss_size  uint32
-	ss_flags int32
-}
-
 type sigset struct {
 	__bits [4]uint32
 }

src/runtime/defs_linux_386.go

@@ -168,7 +168,7 @@ type siginfo struct {
 	si_addr uint32
 }
 
-type sigaltstackt struct {
+type stackt struct {
 	ss_sp    *byte
 	ss_flags int32
 	ss_size  uintptr
@@ -208,7 +208,7 @@ type sigcontext struct {
 type ucontext struct {
 	uc_flags    uint32
 	uc_link     *ucontext
-	uc_stack    sigaltstackt
+	uc_stack    stackt
 	uc_mcontext sigcontext
 	uc_sigmask  uint32
 }

src/runtime/defs_linux_amd64.go

@@ -205,7 +205,7 @@ type fpreg1 struct {
 	exponent    uint16
 }
 
-type sigaltstackt struct {
+type stackt struct {
 	ss_sp     *byte
 	ss_flags  int32
 	pad_cgo_0 [4]byte
@@ -221,7 +221,7 @@ type mcontext struct {
 type ucontext struct {
 	uc_flags     uint64
 	uc_link      *ucontext
-	uc_stack     sigaltstackt
+	uc_stack     stackt
 	uc_mcontext  mcontext
 	uc_sigmask   usigset
 	__fpregs_mem fpstate

src/runtime/defs_linux_arm.go

@@ -101,7 +101,7 @@ func (ts *timespec) set_nsec(x int32) {
 	ts.tv_nsec = x
 }
 
-type sigaltstackt struct {
+type stackt struct {
 	ss_sp    *byte
 	ss_flags int32
 	ss_size  uintptr
@@ -134,7 +134,7 @@ type sigcontext struct {
 type ucontext struct {
 	uc_flags    uint32
 	uc_link     *ucontext
-	uc_stack    sigaltstackt
+	uc_stack    stackt
 	uc_mcontext sigcontext
 	uc_sigmask  uint32
 	__unused    [31]int32

src/runtime/defs_linux_arm64.go

@@ -153,7 +153,7 @@ type usigset struct {
 	__val [16]uint64
 }
 
-type sigaltstackt struct {
+type stackt struct {
 	ss_sp     *byte
 	ss_flags  int32
 	pad_cgo_0 [4]byte
@@ -179,7 +179,7 @@ type sockaddr_un struct {
 type ucontext struct {
 	uc_flags    uint64
 	uc_link     *ucontext
-	uc_stack    sigaltstackt
+	uc_stack    stackt
 	uc_sigmask  uint64
 	_pad        [(1024 - 64) / 8]byte
 	_pad2       [8]byte // sigcontext must be aligned to 16-byte

src/runtime/defs_linux_mips64x.go

@@ -150,7 +150,7 @@ const (
 	_SA_RESTORER = 0
 )
 
-type sigaltstackt struct {
+type stackt struct {
 	ss_sp    *byte
 	ss_size  uintptr
 	ss_flags int32
@@ -177,7 +177,7 @@ type sigcontext struct {
 type ucontext struct {
 	uc_flags    uint64
 	uc_link     *ucontext
-	uc_stack    sigaltstackt
+	uc_stack    stackt
 	uc_mcontext sigcontext
 	uc_sigmask  uint64
 }

src/runtime/defs_linux_ppc64.go

@@ -170,7 +170,7 @@ type vreg struct {
 	u [4]uint32
 }
 
-type sigaltstackt struct {
+type stackt struct {
 	ss_sp     *byte
 	ss_flags  int32
 	pad_cgo_0 [4]byte
@@ -193,7 +193,7 @@ type sigcontext struct {
 type ucontext struct {
 	uc_flags    uint64
 	uc_link     *ucontext
-	uc_stack    sigaltstackt
+	uc_stack    stackt
 	uc_sigmask  uint64
 	__unused    [15]uint64
 	uc_mcontext sigcontext

src/runtime/defs_linux_ppc64le.go

@@ -170,7 +170,7 @@ type vreg struct {
 	u [4]uint32
 }
 
-type sigaltstackt struct {
+type stackt struct {
 	ss_sp     *byte
 	ss_flags  int32
 	pad_cgo_0 [4]byte
@@ -193,7 +193,7 @@ type sigcontext struct {
 type ucontext struct {
 	uc_flags    uint64
 	uc_link     *ucontext
-	uc_stack    sigaltstackt
+	uc_stack    stackt
 	uc_sigmask  uint64
 	__unused    [15]uint64
 	uc_mcontext sigcontext

src/runtime/defs_linux_s390x.go

@@ -143,7 +143,7 @@ const (
 	_SA_RESTORER = 0
 )
 
-type sigaltstackt struct {
+type stackt struct {
 	ss_sp    *byte
 	ss_flags int32
 	ss_size  uintptr
@@ -161,7 +161,7 @@ type sigcontext struct {
 type ucontext struct {
 	uc_flags    uint64
 	uc_link     *ucontext
-	uc_stack    sigaltstackt
+	uc_stack    stackt
 	uc_mcontext sigcontext
 	uc_sigmask  uint64
 }

src/runtime/defs_netbsd.go

@@ -109,7 +109,6 @@ const (
 	EVFILT_WRITE = C.EVFILT_WRITE
 )
 
-type SigaltstackT C.struct_sigaltstack
 type Sigset C.sigset_t
 type Siginfo C.struct__ksiginfo
 

src/runtime/defs_openbsd.go

@@ -106,7 +106,6 @@ const (
 
 type TforkT C.struct___tfork
 
-type SigaltstackT C.struct_sigaltstack
 type Sigcontext C.struct_sigcontext
 type Siginfo C.siginfo_t
 type Sigset C.sigset_t

src/runtime/defs_openbsd_386.go

@@ -90,12 +90,6 @@ type tforkt struct {
 	tf_stack uintptr
 }
 
-type sigaltstackt struct {
-	ss_sp    uintptr
-	ss_size  uintptr
-	ss_flags int32
-}
-
 type sigcontext struct {
 	sc_gs       uint32
 	sc_fs       uint32

src/runtime/defs_openbsd_amd64.go

@@ -90,13 +90,6 @@ type tforkt struct {
 	tf_stack uintptr
 }
 
-type sigaltstackt struct {
-	ss_sp     uintptr
-	ss_size   uintptr
-	ss_flags  int32
-	pad_cgo_0 [4]byte
-}
-
 type sigcontext struct {
 	sc_rdi      uint64
 	sc_rsi      uint64

src/runtime/defs_openbsd_arm.go

@@ -90,12 +90,6 @@ type tforkt struct {
 	tf_stack uintptr
 }
 
-type sigaltstackt struct {
-	ss_sp    uintptr
-	ss_size  uintptr
-	ss_flags int32
-}
-
 type sigcontext struct {
 	__sc_unused int32
 	sc_mask     int32

src/runtime/defs_solaris.go

@@ -133,7 +133,6 @@ const (
 
 type SemT C.sem_t
 
-type SigaltstackT C.struct_sigaltstack
 type Sigset C.sigset_t
 type StackT C.stack_t
 

src/runtime/os3_solaris.go

@@ -209,22 +209,8 @@ func miniterrno()
 func minit() {
 	_g_ := getg()
 	asmcgocall(unsafe.Pointer(funcPC(miniterrno)), unsafe.Pointer(&libc____errno))
-	// Initialize signal handling
-	var st sigaltstackt
-	sigaltstack(nil, &st)
-	if st.ss_flags&_SS_DISABLE != 0 {
-		signalstack(&_g_.m.gsignal.stack)
-		_g_.m.newSigstack = true
-	} else {
-		// Use existing signal stack.
-		stsp := uintptr(unsafe.Pointer(st.ss_sp))
-		_g_.m.gsignal.stack.lo = stsp
-		_g_.m.gsignal.stack.hi = stsp + uintptr(st.ss_size)
-		_g_.m.gsignal.stackguard0 = stsp + _StackGuard
-		_g_.m.gsignal.stackguard1 = stsp + _StackGuard
-		_g_.m.gsignal.stackAlloc = uintptr(st.ss_size)
-		_g_.m.newSigstack = false
-	}
+
+	minitSignalStack()
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -318,17 +304,10 @@ func getsig(i int32) uintptr {
 	return *((*uintptr)(unsafe.Pointer(&sa._funcptr)))
 }
 
+// setSignaltstackSP sets the ss_sp field of a stackt.
 //go:nosplit
-func signalstack(s *stack) {
-	var st sigaltstackt
-	if s == nil {
-		st.ss_flags = _SS_DISABLE
-	} else {
-		st.ss_sp = (*byte)(unsafe.Pointer(s.lo))
-		st.ss_size = uint64(s.hi - s.lo)
-		st.ss_flags = 0
-	}
-	sigaltstack(&st, nil)
+func setSignalstackSP(s *stackt, sp uintptr) {
+	s.ss_sp = (*byte)(unsafe.Pointer(sp))
 }
 
 //go:nosplit
@@ -539,7 +518,7 @@ func sigaction(sig int32, act *sigactiont, oact *sigactiont) /* int32 */ {
 
 //go:nosplit
 //go:nowritebarrierrec
-func sigaltstack(ss *sigaltstackt, oss *sigaltstackt) /* int32 */ {
+func sigaltstack(ss *stackt, oss *stackt) /* int32 */ {
 	sysvicall2(&libc_sigaltstack, uintptr(unsafe.Pointer(ss)), uintptr(unsafe.Pointer(oss)))
 }
 

src/runtime/os_darwin.go

@@ -183,21 +183,7 @@ func minit() {
 	// The signal handler handles it directly.
 	// The sigaltstack assembly function does nothing.
 	if GOARCH != "arm" && GOARCH != "arm64" {
-		var st stackt
-		sigaltstack(nil, &st)
-		if st.ss_flags&_SS_DISABLE != 0 {
-			signalstack(&_g_.m.gsignal.stack)
-			_g_.m.newSigstack = true
-		} else {
-			// Use existing signal stack.
-			stsp := uintptr(unsafe.Pointer(st.ss_sp))
-			_g_.m.gsignal.stack.lo = stsp
-			_g_.m.gsignal.stack.hi = stsp + st.ss_size
-			_g_.m.gsignal.stackguard0 = stsp + _StackGuard
-			_g_.m.gsignal.stackguard1 = stsp + _StackGuard
-			_g_.m.gsignal.stackAlloc = st.ss_size
-			_g_.m.newSigstack = false
-		}
+		minitSignalStack()
 	}
 
 	// restore signal mask from m.sigmask and unblock essential signals
@@ -563,17 +549,10 @@ func getsig(i int32) uintptr {
 	return *(*uintptr)(unsafe.Pointer(&sa.__sigaction_u))
 }
 
+// setSignaltstackSP sets the ss_sp field of a stackt.
 //go:nosplit
-func signalstack(s *stack) {
-	var st stackt
-	if s == nil {
-		st.ss_flags = _SS_DISABLE
-	} else {
-		st.ss_sp = (*byte)(unsafe.Pointer(s.lo))
-		st.ss_size = s.hi - s.lo
-		st.ss_flags = 0
-	}
-	sigaltstack(&st, nil)
+func setSignalstackSP(s *stackt, sp uintptr) {
+	s.ss_sp = (*byte)(unsafe.Pointer(sp))
 }
 
 //go:nosplit

src/runtime/os_dragonfly.go

@@ -22,7 +22,7 @@ type mOS struct{}
 func lwp_create(param *lwpparams) int32
 
 //go:noescape
-func sigaltstack(new, old *sigaltstackt)
+func sigaltstack(new, old *stackt)
 
 //go:noescape
 func sigaction(sig int32, new, old *sigactiont)
@@ -185,22 +185,7 @@ func minit() {
 	// m.procid is a uint64, but lwp_start writes an int32. Fix it up.
 	_g_.m.procid = uint64(*(*int32)(unsafe.Pointer(&_g_.m.procid)))
 
-	// Initialize signal handling.
-	var st sigaltstackt
-	sigaltstack(nil, &st)
-	if st.ss_flags&_SS_DISABLE != 0 {
-		signalstack(&_g_.m.gsignal.stack)
-		_g_.m.newSigstack = true
-	} else {
-		// Use existing signal stack.
-		stsp := uintptr(unsafe.Pointer(st.ss_sp))
-		_g_.m.gsignal.stack.lo = stsp
-		_g_.m.gsignal.stack.hi = stsp + st.ss_size
-		_g_.m.gsignal.stackguard0 = stsp + _StackGuard
-		_g_.m.gsignal.stackguard1 = stsp + _StackGuard
-		_g_.m.gsignal.stackAlloc = st.ss_size
-		_g_.m.newSigstack = false
-	}
+	minitSignalStack()
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -292,17 +277,10 @@ func getsig(i int32) uintptr {
 	return sa.sa_sigaction
 }
 
+// setSignaltstackSP sets the ss_sp field of a stackt.
 //go:nosplit
-func signalstack(s *stack) {
-	var st sigaltstackt
-	if s == nil {
-		st.ss_flags = _SS_DISABLE
-	} else {
-		st.ss_sp = s.lo
-		st.ss_size = s.hi - s.lo
-		st.ss_flags = 0
-	}
-	sigaltstack(&st, nil)
+func setSignalstackSP(s *stackt, sp uintptr) {
+	s.ss_sp = sp
 }
 
 //go:nosplit

src/runtime/os_freebsd.go

@@ -175,22 +175,7 @@ func minit() {
 		_g_.m.procid = uint64(*(*uint32)(unsafe.Pointer(&_g_.m.procid)))
 	}
 
-	// Initialize signal handling.
-	var st stackt
-	sigaltstack(nil, &st)
-	if st.ss_flags&_SS_DISABLE != 0 {
-		signalstack(&_g_.m.gsignal.stack)
-		_g_.m.newSigstack = true
-	} else {
-		// Use existing signal stack.
-		stsp := uintptr(unsafe.Pointer(st.ss_sp))
-		_g_.m.gsignal.stack.lo = stsp
-		_g_.m.gsignal.stack.hi = stsp + st.ss_size
-		_g_.m.gsignal.stackguard0 = stsp + _StackGuard
-		_g_.m.gsignal.stackguard1 = stsp + _StackGuard
-		_g_.m.gsignal.stackAlloc = st.ss_size
-		_g_.m.newSigstack = false
-	}
+	minitSignalStack()
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -282,17 +267,10 @@ func getsig(i int32) uintptr {
 	return sa.sa_handler
 }
 
+// setSignaltstackSP sets the ss_sp field of a stackt.
 //go:nosplit
-func signalstack(s *stack) {
-	var st stackt
-	if s == nil {
-		st.ss_flags = _SS_DISABLE
-	} else {
-		st.ss_sp = s.lo
-		st.ss_size = s.hi - s.lo
-		st.ss_flags = 0
-	}
-	sigaltstack(&st, nil)
+func setSignalstackSP(s *stackt, sp uintptr) {
+	s.ss_sp = sp
 }
 
 //go:nosplit

src/runtime/os_linux.go

@@ -260,21 +260,7 @@ func minit() {
 	// Initialize signal handling.
 	_g_ := getg()
 
-	var st sigaltstackt
-	sigaltstack(nil, &st)
-	if st.ss_flags&_SS_DISABLE != 0 {
-		signalstack(&_g_.m.gsignal.stack)
-		_g_.m.newSigstack = true
-	} else {
-		// Use existing signal stack.
-		stsp := uintptr(unsafe.Pointer(st.ss_sp))
-		_g_.m.gsignal.stack.lo = stsp
-		_g_.m.gsignal.stack.hi = stsp + st.ss_size
-		_g_.m.gsignal.stackguard0 = stsp + _StackGuard
-		_g_.m.gsignal.stackguard1 = stsp + _StackGuard
-		_g_.m.gsignal.stackAlloc = st.ss_size
-		_g_.m.newSigstack = false
-	}
+	minitSignalStack()
 
 	// for debuggers, in case cgo created the thread
 	_g_.m.procid = uint64(gettid())
@@ -341,7 +327,7 @@ func cgoSigtramp()
 func rt_sigaction(sig uintptr, new, old *sigactiont, size uintptr) int32
 
 //go:noescape
-func sigaltstack(new, old *sigaltstackt)
+func sigaltstack(new, old *stackt)
 
 //go:noescape
 func setitimer(mode int32, new, old *itimerval)
@@ -419,15 +405,8 @@ func getsig(i int32) uintptr {
 	return sa.sa_handler
 }
 
+// setSignaltstackSP sets the ss_sp field of a stackt.
 //go:nosplit
-func signalstack(s *stack) {
-	var st sigaltstackt
-	if s == nil {
-		st.ss_flags = _SS_DISABLE
-	} else {
-		st.ss_sp = (*byte)(unsafe.Pointer(s.lo))
-		st.ss_size = s.hi - s.lo
-		st.ss_flags = 0
-	}
-	sigaltstack(&st, nil)
+func setSignalstackSP(s *stackt, sp uintptr) {
+	s.ss_sp = (*byte)(unsafe.Pointer(sp))
 }

src/runtime/os_netbsd.go

@@ -35,7 +35,7 @@ func setitimer(mode int32, new, old *itimerval)
 func sigaction(sig int32, new, old *sigactiont)
 
 //go:noescape
-func sigaltstack(new, old *sigaltstackt)
+func sigaltstack(new, old *stackt)
 
 //go:noescape
 func sigprocmask(how int32, new, old *sigset)
@@ -303,17 +303,10 @@ func getsig(i int32) uintptr {
 	return sa.sa_sigaction
 }
 
+// setSignaltstackSP sets the ss_sp field of a stackt.
 //go:nosplit
-func signalstack(s *stack) {
-	var st sigaltstackt
-	if s == nil {
-		st.ss_flags = _SS_DISABLE
-	} else {
-		st.ss_sp = s.lo
-		st.ss_size = s.hi - s.lo
-		st.ss_flags = 0
-	}
-	sigaltstack(&st, nil)
+func setSignalstackSP(s *stackt, sp uintptr) {
+	s.ss_sp = sp
 }
 
 //go:nosplit

src/runtime/os_openbsd.go

@@ -218,22 +218,7 @@ func minit() {
 	// m.procid is a uint64, but tfork writes an int32. Fix it up.
 	_g_.m.procid = uint64(*(*int32)(unsafe.Pointer(&_g_.m.procid)))
 
-	// Initialize signal handling
-	var st stackt
-	sigaltstack(nil, &st)
-	if st.ss_flags&_SS_DISABLE != 0 {
-		signalstack(&_g_.m.gsignal.stack)
-		_g_.m.newSigstack = true
-	} else {
-		// Use existing signal stack.
-		stsp := uintptr(unsafe.Pointer(st.ss_sp))
-		_g_.m.gsignal.stack.lo = stsp
-		_g_.m.gsignal.stack.hi = stsp + st.ss_size
-		_g_.m.gsignal.stackguard0 = stsp + _StackGuard
-		_g_.m.gsignal.stackguard1 = stsp + _StackGuard
-		_g_.m.gsignal.stackAlloc = st.ss_size
-		_g_.m.newSigstack = false
-	}
+	minitSignalStack()
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -298,17 +283,10 @@ func getsig(i int32) uintptr {
 	return sa.sa_sigaction
 }
 
+// setSignaltstackSP sets the ss_sp field of a stackt.
 //go:nosplit
-func signalstack(s *stack) {
-	var st stackt
-	if s == nil {
-		st.ss_flags = _SS_DISABLE
-	} else {
-		st.ss_sp = s.lo
-		st.ss_size = s.hi - s.lo
-		st.ss_flags = 0
-	}
-	sigaltstack(&st, nil)
+func setSignalstackSP(s *stackt, sp uintptr) {
+	s.ss_sp = sp
 }
 
 //go:nosplit

src/runtime/signal_darwin.go

@@ -77,11 +77,7 @@ func sigtrampgo(fn uintptr, infostyle, sig uint32, info *siginfo, ctx unsafe.Poi
 			setg(nil)
 			cgocallback(unsafe.Pointer(funcPC(sigNotOnStack)), noescape(unsafe.Pointer(&sig)), unsafe.Sizeof(sig), 0)
 		}
-		g.m.gsignal.stack.lo = stsp
-		g.m.gsignal.stack.hi = stsp + st.ss_size
-		g.m.gsignal.stackguard0 = stsp + _StackGuard
-		g.m.gsignal.stackguard1 = stsp + _StackGuard
-		g.m.gsignal.stackAlloc = st.ss_size
+		setGsignalStack(&st)
 		g.m.gsignal.stktopsp = getcallersp(unsafe.Pointer(&sig))
 	}
 

src/runtime/signal_freebsd.go

@@ -73,11 +73,7 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 			setg(nil)
 			cgocallback(unsafe.Pointer(funcPC(sigNotOnStack)), noescape(unsafe.Pointer(&sig)), unsafe.Sizeof(sig), 0)
 		}
-		g.m.gsignal.stack.lo = stsp
-		g.m.gsignal.stack.hi = stsp + st.ss_size
-		g.m.gsignal.stackguard0 = stsp + _StackGuard
-		g.m.gsignal.stackguard1 = stsp + _StackGuard
-		g.m.gsignal.stackAlloc = st.ss_size
+		setGsignalStack(&st)
 		g.m.gsignal.stktopsp = getcallersp(unsafe.Pointer(&sig))
 	}
 

src/runtime/signal_openbsd.go

@@ -73,11 +73,7 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 			setg(nil)
 			cgocallback(unsafe.Pointer(funcPC(sigNotOnStack)), noescape(unsafe.Pointer(&sig)), unsafe.Sizeof(sig), 0)
 		}
-		g.m.gsignal.stack.lo = stsp
-		g.m.gsignal.stack.hi = stsp + st.ss_size
-		g.m.gsignal.stackguard0 = stsp + _StackGuard
-		g.m.gsignal.stackguard1 = stsp + _StackGuard
-		g.m.gsignal.stackAlloc = st.ss_size
+		setGsignalStack(&st)
 		g.m.gsignal.stktopsp = getcallersp(unsafe.Pointer(&sig))
 	}
 

src/runtime/signal_sigtramp.go

@@ -33,7 +33,7 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 	// If some non-Go code called sigaltstack, adjust.
 	sp := uintptr(unsafe.Pointer(&sig))
 	if sp < g.m.gsignal.stack.lo || sp >= g.m.gsignal.stack.hi {
-		var st sigaltstackt
+		var st stackt
 		sigaltstack(nil, &st)
 		if st.ss_flags&_SS_DISABLE != 0 {
 			setg(nil)
@@ -44,11 +44,7 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 			setg(nil)
 			cgocallback(unsafe.Pointer(funcPC(sigNotOnStack)), noescape(unsafe.Pointer(&sig)), unsafe.Sizeof(sig), 0)
 		}
-		g.m.gsignal.stack.lo = stsp
-		g.m.gsignal.stack.hi = stsp + st.ss_size
-		g.m.gsignal.stackguard0 = stsp + _StackGuard
-		g.m.gsignal.stackguard1 = stsp + _StackGuard
-		g.m.gsignal.stackAlloc = st.ss_size
+		setGsignalStack(&st)
 		g.m.gsignal.stktopsp = getcallersp(unsafe.Pointer(&sig))
 	}
 

src/runtime/signal_unix.go

@@ -525,6 +525,58 @@ func unblocksig(sig int32) {
 	sigprocmask(_SIG_UNBLOCK, &set, nil)
 }
 
+// minitSignalStack is called when initializing a new m to set the
+// alternate signal stack. If the alternate signal stack is not set
+// for the thread (the normal case) then set the alternate signal
+// stack to the gsignal stack. If the alternate signal stack is set
+// for the thread (the case when a non-Go thread sets the alternate
+// signal stack and then calls a Go function) then set the gsignal
+// stack to the alternate signal stack. Record which choice was made
+// in newSigstack, so that it can be undone in unminit.
+func minitSignalStack() {
+	_g_ := getg()
+	var st stackt
+	sigaltstack(nil, &st)
+	if st.ss_flags&_SS_DISABLE != 0 {
+		signalstack(&_g_.m.gsignal.stack)
+		_g_.m.newSigstack = true
+	} else {
+		setGsignalStack(&st)
+		_g_.m.newSigstack = false
+	}
+}
+
+// setGsignalStack sets the gsignal stack of the current m to an
+// alternate signal stack returned from the sigaltstack system call.
+// This is used when handling a signal if non-Go code has set the
+// alternate signal stack.
+//go:nosplit
+//go:nowritebarrierrec
+func setGsignalStack(st *stackt) {
+	g := getg()
+	stsp := uintptr(unsafe.Pointer(st.ss_sp))
+	g.m.gsignal.stack.lo = stsp
+	g.m.gsignal.stack.hi = stsp + st.ss_size
+	g.m.gsignal.stackguard0 = stsp + _StackGuard
+	g.m.gsignal.stackguard1 = stsp + _StackGuard
+	g.m.gsignal.stackAlloc = st.ss_size
+}
+
+// signalstack sets the current thread's alternate signal stack to s.
+// If s is nil, the current thread's alternate signal stack is disabled.
+//go:nosplit
+func signalstack(s *stack) {
+	var st stackt
+	if s == nil {
+		st.ss_flags = _SS_DISABLE
+	} else {
+		setSignalstackSP(&st, s.lo)
+		st.ss_size = s.hi - s.lo
+		st.ss_flags = 0
+	}
+	sigaltstack(&st, nil)
+}
+
 // setsigsegv is used on darwin/arm{,64} to fake a segmentation fault.
 //go:nosplit
 func setsigsegv(pc uintptr) {