runtime/cgo: remove SIGSEGV emulation on iOS

The misc/ios exec wrapper doesn't support lldb since https://go.dev/cl/573175.
This means that the SIGSEGV emulation code in the cgo signal handling on
iOS is no longer needed, and can be removed.

Cq-Include-Trybots: luci.golang.try:gotip-darwin-arm64_26
Change-Id: I39827cb20756e4730352d87cb3514bb6a3f1cee8
Reviewed-on: https://go-review.googlesource.com/c/go/+/756800
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

7 files changed, 0 insertions, 331 deletions

diff --git a/src/runtime/cgo/gcc_ios_arm64.c b/src/runtime/cgo/gcc_ios_arm64.c
index 32f517d464..bef2750cd1 100644
--- a/src/runtime/cgo/gcc_ios_arm64.c
+++ b/src/runtime/cgo/gcc_ios_arm64.c
@@ -10,22 +10,8 @@
 
 #include "libcgo.h"
 
-#include <TargetConditionals.h>
-
-#if TARGET_OS_IPHONE
 #include <CoreFoundation/CFBundle.h>
 #include <CoreFoundation/CFString.h>
-#endif
-
-#if TARGET_OS_IPHONE
-
-static void
-threadentry_platform(void)
-{
-#if TARGET_OS_IPHONE
-	darwin_arm_init_thread_exception_port();
-#endif
-}
 
 // init_working_dir sets the current working directory to the app root.
 // By default ios/arm64 processes start in "/".
@@ -87,17 +73,10 @@ init_working_dir()
 	}
 }
 
-#endif // TARGET_OS_IPHONE
-
 static void
 init_platform()
 {
-#if TARGET_OS_IPHONE
-	darwin_arm_init_mach_exception_handler();
-	darwin_arm_init_thread_exception_port();
 	init_working_dir();
-#endif
 }
 
 void (*x_cgo_init_platform)(void) = init_platform;
-void (*x_cgo_threadentry_platform)(void) = threadentry_platform;
diff --git a/src/runtime/cgo/gcc_signal2_ios_arm64.c b/src/runtime/cgo/gcc_signal2_ios_arm64.c
deleted file mode 100644
index f8cef54f6a..0000000000
--- a/src/runtime/cgo/gcc_signal2_ios_arm64.c
+++ /dev/null
@@ -1,11 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//go:build lldb
-
-// Used by gcc_signal_darwin_arm64.c when doing the test build during cgo.
-// We hope that for real binaries the definition provided by Go will take precedence
-// and the linker will drop this .o file altogether, which is why this definition
-// is all by itself in its own file.
-void __attribute__((weak)) xx_cgo_panicmem(void) {}
diff --git a/src/runtime/cgo/gcc_signal_ios_arm64.c b/src/runtime/cgo/gcc_signal_ios_arm64.c
deleted file mode 100644
index 3872f62de1..0000000000
--- a/src/runtime/cgo/gcc_signal_ios_arm64.c
+++ /dev/null
@@ -1,213 +0,0 @@
-// Copyright 2015 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Emulation of the Unix signal SIGSEGV.
-//
-// On iOS, Go tests and apps under development are run by lldb.
-// The debugger uses a task-level exception handler to intercept signals.
-// Despite having a 'handle' mechanism like gdb, lldb will not allow a
-// SIGSEGV to pass to the running program. For Go, this means we cannot
-// generate a panic, which cannot be recovered, and so tests fail.
-//
-// We work around this by registering a thread-level mach exception handler
-// and intercepting EXC_BAD_ACCESS. The kernel offers thread handlers a
-// chance to resolve exceptions before the task handler, so we can generate
-// the panic and avoid lldb's SIGSEGV handler.
-//
-// The dist tool enables this by build flag when testing.
-
-//go:build lldb
-
-#include <limits.h>
-#include <pthread.h>
-#include <stdio.h>
-#include <signal.h>
-#include <stdlib.h>
-#include <unistd.h>
-
-#include <mach/arm/thread_status.h>
-#include <mach/exception_types.h>
-#include <mach/mach.h>
-#include <mach/mach_init.h>
-#include <mach/mach_port.h>
-#include <mach/thread_act.h>
-#include <mach/thread_status.h>
-
-#include "libcgo.h"
-#include "libcgo_unix.h"
-
-void xx_cgo_panicmem(void);
-uintptr_t x_cgo_panicmem = (uintptr_t)xx_cgo_panicmem;
-
-static pthread_mutex_t mach_exception_handler_port_set_mu;
-static mach_port_t mach_exception_handler_port_set = MACH_PORT_NULL;
-
-kern_return_t
-catch_exception_raise(
-	mach_port_t exception_port,
-	mach_port_t thread,
-	mach_port_t task,
-	exception_type_t exception,
-	exception_data_t code_vector,
-	mach_msg_type_number_t code_count)
-{
-	kern_return_t ret;
-	arm_unified_thread_state_t thread_state;
-	mach_msg_type_number_t state_count = ARM_UNIFIED_THREAD_STATE_COUNT;
-
-	// Returning KERN_SUCCESS intercepts the exception.
-	//
-	// Returning KERN_FAILURE lets the exception fall through to the
-	// next handler, which is the standard signal emulation code
-	// registered on the task port.
-
-	if (exception != EXC_BAD_ACCESS) {
-		return KERN_FAILURE;
-	}
-
-	ret = thread_get_state(thread, ARM_UNIFIED_THREAD_STATE, (thread_state_t)&thread_state, &state_count);
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: thread_get_state failed: %d\n", ret);
-		abort();
-	}
-
-	// Bounce call to sigpanic through asm that makes it look like
-	// we call sigpanic directly from the faulting code.
-#ifdef __arm64__
-	thread_state.ts_64.__x[1] = thread_state.ts_64.__lr;
-	thread_state.ts_64.__x[2] = thread_state.ts_64.__pc;
-	thread_state.ts_64.__pc = x_cgo_panicmem;
-#else
-	thread_state.ts_32.__r[1] = thread_state.ts_32.__lr;
-	thread_state.ts_32.__r[2] = thread_state.ts_32.__pc;
-	thread_state.ts_32.__pc = x_cgo_panicmem;
-#endif
-
-	if (0) {
-		// Useful debugging logic when panicmem is broken.
-		//
-		// Sends the first SIGSEGV and lets lldb catch the
-		// second one, avoiding a loop that locks up iOS
-		// devices requiring a hard reboot.
-		fprintf(stderr, "runtime/cgo: caught exc_bad_access\n");
-		fprintf(stderr, "__lr = %llx\n", thread_state.ts_64.__lr);
-		fprintf(stderr, "__pc = %llx\n", thread_state.ts_64.__pc);
-		static int pass1 = 0;
-		if (pass1) {
-			return KERN_FAILURE;
-		}
-		pass1 = 1;
-	}
-
-	ret = thread_set_state(thread, ARM_UNIFIED_THREAD_STATE, (thread_state_t)&thread_state, state_count);
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: thread_set_state failed: %d\n", ret);
-		abort();
-	}
-
-	return KERN_SUCCESS;
-}
-
-void
-darwin_arm_init_thread_exception_port()
-{
-	// Called by each new OS thread to bind its EXC_BAD_ACCESS exception
-	// to mach_exception_handler_port_set.
-	int ret;
-	mach_port_t port = MACH_PORT_NULL;
-
-	ret = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &port);
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: mach_port_allocate failed: %d\n", ret);
-		abort();
-	}
-	ret = mach_port_insert_right(
-		mach_task_self(),
-		port,
-		port,
-		MACH_MSG_TYPE_MAKE_SEND);
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: mach_port_insert_right failed: %d\n", ret);
-		abort();
-	}
-
-	ret = thread_set_exception_ports(
-		mach_thread_self(),
-		EXC_MASK_BAD_ACCESS,
-		port,
-		EXCEPTION_DEFAULT,
-		THREAD_STATE_NONE);
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: thread_set_exception_ports failed: %d\n", ret);
-		abort();
-	}
-
-	ret = pthread_mutex_lock(&mach_exception_handler_port_set_mu);
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: pthread_mutex_lock failed: %d\n", ret);
-		abort();
-	}
-	ret = mach_port_move_member(
-		mach_task_self(),
-		port,
-		mach_exception_handler_port_set);
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: mach_port_move_member failed: %d\n", ret);
-		abort();
-	}
-	ret = pthread_mutex_unlock(&mach_exception_handler_port_set_mu);
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: pthread_mutex_unlock failed: %d\n", ret);
-		abort();
-	}
-}
-
-static void*
-mach_exception_handler(void *port)
-{
-	// Calls catch_exception_raise.
-	extern boolean_t exc_server();
-	mach_msg_server(exc_server, 2048, (mach_port_t)(uintptr_t)port, 0);
-	abort(); // never returns
-}
-
-void
-darwin_arm_init_mach_exception_handler()
-{
-	pthread_mutex_init(&mach_exception_handler_port_set_mu, NULL);
-
-	// Called once per process to initialize a mach port server, listening
-	// for EXC_BAD_ACCESS thread exceptions.
-	int ret;
-	pthread_t thr = NULL;
-	pthread_attr_t attr;
-	sigset_t ign, oset;
-
-	ret = mach_port_allocate(
-		mach_task_self(),
-		MACH_PORT_RIGHT_PORT_SET,
-		&mach_exception_handler_port_set);
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: mach_port_allocate failed for port_set: %d\n", ret);
-		abort();
-	}
-
-	// Block all signals to the exception handler thread
-	sigfillset(&ign);
-	pthread_sigmask(SIG_SETMASK, &ign, &oset);
-
-	// Start a thread to handle exceptions.
-	uintptr_t port_set = (uintptr_t)mach_exception_handler_port_set;
-	pthread_attr_init(&attr);
-	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
-	ret = _cgo_try_pthread_create(&thr, &attr, mach_exception_handler, (void*)port_set);
-
-	pthread_sigmask(SIG_SETMASK, &oset, nil);
-
-	if (ret) {
-		fprintf(stderr, "runtime/cgo: pthread_create failed: %d\n", ret);
-		abort();
-	}
-	pthread_attr_destroy(&attr);
-}
diff --git a/src/runtime/cgo/gcc_signal_ios_nolldb.c b/src/runtime/cgo/gcc_signal_ios_nolldb.c
deleted file mode 100644
index 9ddc37a013..0000000000
--- a/src/runtime/cgo/gcc_signal_ios_nolldb.c
+++ /dev/null
@@ -1,10 +0,0 @@
-// Copyright 2015 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//go:build !lldb && ios && arm64
-
-#include <stdint.h>
-
-void darwin_arm_init_thread_exception_port() {}
-void darwin_arm_init_mach_exception_handler() {}
diff --git a/src/runtime/cgo/libcgo.h b/src/runtime/cgo/libcgo.h
index ae0542df36..24475b7c43 100644
--- a/src/runtime/cgo/libcgo.h
+++ b/src/runtime/cgo/libcgo.h
@@ -86,16 +86,6 @@ void crosscall1(void (*fn)(void), void (*setg_gcc)(void*), void *g);
 void fatalf(const char* format, ...) __attribute__ ((noreturn));
 
 /*
- * Registers the current mach thread port for EXC_BAD_ACCESS processing.
- */
-void darwin_arm_init_thread_exception_port(void);
-
-/*
- * Starts a mach message server processing EXC_BAD_ACCESS.
- */
-void darwin_arm_init_mach_exception_handler(void);
-
-/*
  * The cgo traceback callback. See runtime.SetCgoTraceback.
  */
 struct cgoTracebackArg {
diff --git a/src/runtime/cgo/signal_ios_arm64.go b/src/runtime/cgo/signal_ios_arm64.go
deleted file mode 100644
index 3425c448c4..0000000000
--- a/src/runtime/cgo/signal_ios_arm64.go
+++ /dev/null
@@ -1,10 +0,0 @@
-// Copyright 2015 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package cgo
-
-import _ "unsafe"
-
-//go:cgo_export_static xx_cgo_panicmem xx_cgo_panicmem
-func xx_cgo_panicmem()
diff --git a/src/runtime/cgo/signal_ios_arm64.s b/src/runtime/cgo/signal_ios_arm64.s
deleted file mode 100644
index 1ae00d13f3..0000000000
--- a/src/runtime/cgo/signal_ios_arm64.s
+++ /dev/null
@@ -1,56 +0,0 @@
-// Copyright 2015 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include "textflag.h"
-
-// xx_cgo_panicmem is the entrypoint for SIGSEGV as intercepted via a
-// mach thread port as EXC_BAD_ACCESS. As the segfault may have happened
-// in C code, we first need to load_g then call xx_cgo_panicmem.
-//
-//	R1 - LR at moment of fault
-//	R2 - PC at moment of fault
-TEXT xx_cgo_panicmem(SB),NOSPLIT|NOFRAME,$0
-	// If in external C code, we need to load the g register.
-	BL  runtime·load_g(SB)
-	CMP $0, g
-	BNE ongothread
-
-	// On a foreign thread.
-	// TODO(crawshaw): call badsignal
-	MOVD.W $0, -16(RSP)
-	MOVW $139, R1
-	MOVW R1, 8(RSP)
-	B    runtime·exit(SB)
-
-ongothread:
-	// Trigger a SIGSEGV panic.
-	//
-	// The goal is to arrange the stack so it looks like the runtime
-	// function sigpanic was called from the PC that faulted. It has
-	// to be sigpanic, as the stack unwinding code in traceback.go
-	// looks explicitly for it.
-	//
-	// To do this we call into runtime·setsigsegv, which sets the
-	// appropriate state inside the g object. We give it the faulting
-	// PC on the stack, then put it in the LR before calling sigpanic.
-
-	// Build a 32-byte stack frame for us for this call.
-	// Saved LR (none available) is at the bottom,
-	// then the PC argument for setsigsegv,
-	// then a copy of the LR for us to restore.
-	MOVD.W $0, -32(RSP)
-	MOVD R1, 8(RSP)
-	MOVD R2, 16(RSP)
-	BL runtime·setsigsegv(SB)
-	MOVD 8(RSP), R1
-	MOVD 16(RSP), R2
-
-	// Build a 16-byte stack frame for the simulated
-	// call to sigpanic, by taking 16 bytes away from the
-	// 32-byte stack frame above.
-	// The saved LR in this frame is the LR at time of fault,
-	// and the LR on entry to sigpanic is the PC at time of fault.
-	MOVD.W R1, 16(RSP)
-	MOVD R2, R30
-	B runtime·sigpanic(SB)