Get setcontext() and getcontext() working on Aarch64

This change also adds the missing code for getting and restoring the
thread's signal mask, since that's explicitly listed by the man page

libc/calls/calls.mk

@@ -211,6 +211,12 @@ o/$(MODE)/libc/calls/pledge-linux.o: private		\
 			-Os				\
 			-fPIC
 
+# these assembly files are safe to build on aarch64
+o/$(MODE)/libc/calls/getcontext.o: libc/calls/getcontext.S
+	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) -c $<
+o/$(MODE)/libc/calls/setcontext2.o: libc/calls/setcontext2.S
+	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) -c $<
+
 LIBC_CALLS_LIBS = $(foreach x,$(LIBC_CALLS_ARTIFACTS),$($(x)))
 LIBC_CALLS_SRCS = $(foreach x,$(LIBC_CALLS_ARTIFACTS),$($(x)_SRCS))
 LIBC_CALLS_HDRS = $(foreach x,$(LIBC_CALLS_ARTIFACTS),$($(x)_HDRS))

libc/calls/getcontext.S

@@ -22,6 +22,8 @@
 //
 //	@see	setcontext()
 getcontext:
+#ifdef __x86_64__
+
 	pushf
 	pop	176(%rdi)
 	movaps	%xmm0,480(%rdi)
@@ -61,12 +63,39 @@ getcontext:
 	mov	%rax,160(%rdi)
 	mov	(%rsp),%rax
 	mov	%rax,168(%rdi)
-	xor	%eax,%eax
+	jmp	__getcontext
-	ret
+
+#elif defined(__aarch64__)
+
+	stp	x0,x1,[x0,184]
+	stp	x2,x3,[x0,200]
+	stp	x4,x5,[x0,216]
+	stp	x6,x7,[x0,232]
+	stp	x8,x9,[x0,248]
+	stp	x10,x11,[x0,264]
+	stp	x12,x13,[x0,280]
+	stp	x14,x15,[x0,296]
+	stp	x16,x17,[x0,312]
+	stp	x18,x19,[x0,328]
+	stp	x20,x21,[x0,344]
+	stp	x22,x23,[x0,360]
+	stp	x24,x25,[x0,376]
+	stp	x26,x27,[x0,392]
+	stp	x28,x29,[x0,408]
+	str	x30,[x0,424]
+	mov	x1,sp
+	str	x1,[x0,432]		// sp = caller's sp
+	str	x30,[x0,440]		// pc = caller's pc
+	b	__getcontext
+
+#else
+#error "unsupported architecture"
+#endif
 	.endfn	getcontext,globl
 
 	.end
 ////////////////////////////////////////////////////////////////////////////////
+
 noasan noubsan dontinstrument int getcontext(ucontext_t *uc) {
   asm volatile("movaps\t%%xmm0,%0" : /* no outputs */ : "m"(uc->__fpustate.xmm[0]));
   asm volatile("movaps\t%%xmm1,%0" : /* no outputs */ : "m"(uc->__fpustate.xmm[1]));
@@ -112,3 +141,11 @@ noasan noubsan dontinstrument int getcontext(ucontext_t *uc) {
                : "rax");
   return 0;
 }
+
+noasan noubsan dontinstrument int getcontext(ucontext_t *uc) {
+  asm volatile("stp\tx0,x1,%0" : "=m"(uc->uc_mcontext.regs[0]));
+  asm volatile("stp\tx2,x3,%0" : "=m"(uc->uc_mcontext.regs[2]));
+  asm volatile("mov\tx1,sp\n\tstr\tx1,%0" : "=m"(uc->uc_mcontext.sp));
+  asm volatile("str\tx30,%0" : "=m"(uc->uc_mcontext.pc));
+  return 0;
+}

libc/calls/getcontext2.c

@@ -0,0 +1,34 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/struct/sigset.h"
+#include "libc/calls/struct/ucontext.internal.h"
+#include "libc/calls/ucontext.h"
+#include "libc/runtime/stack.h"
+#include "libc/sysv/consts/sig.h"
+#include "libc/sysv/consts/ss.h"
+
+// this is tail called by the getcontext() implementation
+int __getcontext(ucontext_t *uc) {
+  uc->uc_flags = 0;
+  uc->uc_link = 0;
+  uc->uc_stack.ss_sp = (void *)uc->uc_mcontext.SP;
+  uc->uc_stack.ss_flags = SS_ONSTACK;
+  uc->uc_stack.ss_size = uc->uc_mcontext.SP - GetStackAddr();
+  return sigprocmask(SIG_SETMASK, 0, &uc->uc_sigmask);
+}

libc/calls/setcontext.c

@@ -0,0 +1,41 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/struct/sigset.h"
+#include "libc/calls/struct/ucontext.internal.h"
+#include "libc/calls/ucontext.h"
+#include "libc/sysv/consts/sig.h"
+#include "libc/sysv/consts/ss.h"
+
+int __setcontext(const ucontext_t *, uintptr_t);
+
+/**
+ * Sets machine context.
+ *
+ * @see getcontext()
+ */
+int setcontext(const ucontext_t *uc) {
+  uintptr_t sp;
+  if (sigprocmask(SIG_SETMASK, &uc->uc_sigmask, 0)) return -1;
+  if (uc->uc_stack.ss_flags & (SS_DISABLE | SS_ONSTACK)) {
+    sp = uc->uc_mcontext.SP;
+  } else {
+    sp = (uintptr_t)uc->uc_stack.ss_sp & -16;
+  }
+  return __setcontext(uc, sp);
+}

libc/calls/setcontext2.S

@@ -18,10 +18,10 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/macros.internal.h"
 
-//	Sets machine state.
+//	tailed called by setcontext() implementation
-//
+__setcontext:
-//	@see	getcontext()
+#ifdef __x86_64__
-setcontext:
+
 	mov	224(%rdi),%rax
 	test	%rax,%rax
 	je	1f
@@ -43,6 +43,7 @@ setcontext:
 	movaps	400(%rax),%xmm15
 1:	push	176(%rdi)
 	popf
+	mov	%rsi,%rsp
 	mov	40(%rdi),%r8
 	mov	48(%rdi),%r9
 	mov	56(%rdi),%r10
@@ -57,16 +58,41 @@ setcontext:
 	mov	136(%rdi),%rdx
 	mov	144(%rdi),%rax
 	mov	152(%rdi),%rcx
-	mov	160(%rdi),%rsp
 	xor	%rax,%rax
 	push	168(%rdi)
 	mov	104(%rdi),%rdi
 	ret
-	.endfn	setcontext,globl
+
+#elif defined(__aarch64__)
+
+	mov	sp,x1			// sp = second argument
+	ldr	x30,[x0,440]		// return address <- pc
+	ldp	x28,x29,[x0,408]	// x0 and x30 discarded
+	ldp	x26,x27,[x0,392]
+	ldp	x24,x25,[x0,376]
+	ldp	x22,x23,[x0,360]
+	ldp	x20,x21,[x0,344]
+	ldp	x18,x19,[x0,328]
+	ldp	x16,x17,[x0,312]
+	ldp	x14,x15,[x0,296]
+	ldp	x12,x13,[x0,280]
+	ldp	x10,x11,[x0,264]
+	ldp	x8,x9,[x0,248]
+	ldp	x6,x7,[x0,232]
+	ldp	x4,x5,[x0,216]
+	ldp	x2,x3,[x0,200]
+	ldr	x1,[x0,192]
+	mov	w0,0
+	ret
+
+#else
+#error "unsupported architecture"
+#endif
+	.endfn	__setcontext,globl
 
 	.end
 ////////////////////////////////////////////////////////////////////////////////
-noasan noubsan int setcontext(const ucontext_t *uc) {
+noasan noubsan int __setcontext(const ucontext_t *uc) {
   if (uc->uc_mcontext.fpregs) {
     asm volatile("movaps\t%0,%%xmm0" : /* no outputs */ : "m"(uc->uc_mcontext.fpregs->xmm[0]));
     asm volatile("movaps\t%0,%%xmm1" : /* no outputs */ : "m"(uc->uc_mcontext.fpregs->xmm[1]));

libc/calls/struct/ucontext.internal.h

@@ -5,6 +5,14 @@
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
 
+#ifdef __x86_64__
+#define SP rsp
+#elif defined(__aarch64__)
+#define SP sp
+#else
+#error "unsupported architecture"
+#endif
+
 void _ntcontext2linux(struct ucontext *, const struct NtContext *) _Hide;
 void _ntlinux2context(struct NtContext *, const ucontext_t *) _Hide;
 

test/libc/calls/getcontext_test.c

@@ -17,13 +17,13 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
+#include "libc/calls/struct/sigset.h"
 #include "libc/calls/ucontext.h"
 #include "libc/runtime/runtime.h"
+#include "libc/sysv/consts/sig.h"
 #include "libc/testlib/ezbench.h"
 #include "libc/testlib/testlib.h"
 
-#ifdef __x86_64__
-
 int x;
 bool ok1;
 bool ok2;
@@ -51,6 +51,25 @@ TEST(getcontext, test) {
   ASSERT_TRUE(ok2);
 }
 
+TEST(getcontext, canReadAndWriteSignalMask) {
+  sigset_t ss, old;
+  volatile int n = 0;
+  sigemptyset(&ss);
+  sigaddset(&ss, SIGUSR1);
+  sigprocmask(SIG_SETMASK, &ss, &old);
+  ASSERT_EQ(0, getcontext(&context));
+  if (!n) {
+    n = 1;
+    ASSERT_TRUE(sigismember(&context.uc_sigmask, SIGUSR1));
+    sigaddset(&context.uc_sigmask, SIGUSR2);
+    setcontext(&context);
+    abort();
+  }
+  sigprocmask(SIG_SETMASK, 0, &ss);
+  ASSERT_TRUE(sigismember(&ss, SIGUSR2));
+  sigprocmask(SIG_SETMASK, &old, 0);
+}
+
 void SetGetContext(void) {
   static int a;
   a = 0;
@@ -64,5 +83,3 @@ void SetGetContext(void) {
 BENCH(getcontext, bench) {
   EZBENCH2("get/setcontext", donothing, SetGetContext());
 }
-
-#endif /* __x86_64__ */