Bring back the old implementation of setjmp() for aarch64.

It looks like we can't really do without these functions. There are too
many ports that for some reason want to make use of them. As Clang
doesn't implement these functions only for AArch64, let that one use the
original version written in assembly.

src/common/assembly.h

@@ -5,16 +5,28 @@
 #ifndef COMMON_ASSEMBLY_H
 #define COMMON_ASSEMBLY_H
 
-#if defined(__arm__)
+#if defined(__aarch64__)
 
 #define ENTRY(name) \
   .text;            \
   .align 2;         \
   .global name;     \
   name:
-#define ALTENTRY ENTRY
+
+#define END(name) .size name, .- name
+
+#elif defined(__arm__)
+
+#define ENTRY(name) \
+  .text;            \
+  .align 2;         \
+  .global name;     \
+  name:
+
 #define END(name) .size name, .- name
 
 #endif
 
+#define ALTENTRY ENTRY
+
 #endif

src/include/setjmp.h

@@ -26,14 +26,29 @@
 #ifndef _SETJMP_H_
 #define _SETJMP_H_
 
-#include <_/cdefs.h>
+#include <_/types.h>
 
-struct __jmp_buf {
+#ifdef __aarch64__
+
+// The compiler doesn't support __builtin_longjmp() and __builtin_setjmp().
+// Implement longjmp() and setjmp() as C library functions. These are
+// less efficient.
+
+typedef __uint64_t jmp_buf[21];
+
+__BEGIN_DECLS
+int setjmp(jmp_buf) __extname("__setjmp");
+__END_DECLS
+
+#else
+
+// The compiler supports __builtin_longjmp() and __builtin_setjmp().
+// Implement longjmp() and setjmp() on top of these intrinsics.
+
+typedef struct __jmp_buf {
   int __val;
   void *__ptr[5];
-};
-typedef struct __jmp_buf jmp_buf[1];
-typedef jmp_buf sigjmp_buf;
+} jmp_buf[1];
 
 #define setjmp(env)                  \
   ({                                 \
@@ -42,6 +57,10 @@ typedef jmp_buf sigjmp_buf;
     __builtin_setjmp(__env->__ptr);  \
     __env->__val;                    \
   })
+
+#endif
+
+typedef jmp_buf sigjmp_buf;
 #define sigsetjmp(env, savemask) setjmp(env)
 
 __BEGIN_DECLS

src/libc/setjmp/longjmp.c

@@ -4,8 +4,7 @@
 
 #include <setjmp.h>
 
-// Clang doesn't provide setjmp()/longjmp() support on some architectures.
-#if !defined(__aarch64__) && !defined(__riscv)
+#ifndef __aarch64__
 
 void longjmp(jmp_buf env, int val) {
   env->__val = val == 0 ? 1 : val;

src/libc/setjmp/longjmp_fallback.S

@@ -0,0 +1,41 @@
+// Copyright (c) 2015-2017 Nuxi, https://nuxi.nl/
+//
+// SPDX-License-Identifier: BSD-2-Clause
+
+#include <common/assembly.h>
+
+#ifdef __aarch64__
+
+ENTRY(longjmp)
+ALTENTRY(siglongjmp)
+  // Restore callee-saved registers.
+  ldp x19, x20, [x0, #0]
+  ldp x21, x22, [x0, #16]
+  ldp x23, x24, [x0, #32]
+  ldp x25, x26, [x0, #48]
+  ldp x27, x28, [x0, #64]
+
+  // Restore frame pointer and link register.
+  ldp x29, x30, [x0, #80]
+
+  // Restore stack pointer.
+  ldr x2, [x0, #96]
+  mov sp, x2
+
+  // Restore VFP registers.
+  ldp d8, d9, [x0, #104]
+  ldp d10, d11, [x0, #120]
+  ldp d12, d13, [x0, #136]
+  ldp d14, d15, [x0, #152]
+
+  // Return the second parameter of longjmp(), ensuring that we never
+  // return zero.
+  mov x0, x1
+  cbnz x0, 1f
+  mov x0, #1
+1:
+  br x30
+END(longjmp)
+END(siglongjmp)
+
+#endif

src/libc/setjmp/setjmp_fallback.S

@@ -0,0 +1,35 @@
+// Copyright (c) 2015-2017 Nuxi, https://nuxi.nl/
+//
+// SPDX-License-Identifier: BSD-2-Clause
+
+#include <common/assembly.h>
+
+#ifdef __aarch64__
+
+ENTRY(__setjmp)
+  // Save callee-saved registers.
+  stp x19, x20, [x0, #0]
+  stp x21, x22, [x0, #16]
+  stp x23, x24, [x0, #32]
+  stp x25, x26, [x0, #48]
+  stp x27, x28, [x0, #64]
+
+  // Save frame pointer and link register.
+  stp x29, x30, [x0, #80]
+
+  // Save stack pointer.
+  mov x1, sp
+  str x1, [x0, #96]
+
+  // Save VFP registers.
+  stp d8, d9, [x0, #104]
+  stp d10, d11, [x0, #120]
+  stp d12, d13, [x0, #136]
+  stp d14, d15, [x0, #152]
+
+  // Return zero for a direct invocation.
+  mov x0, #0
+  ret
+END(setjmp)
+
+#endif

src/libc/setjmp/setjmp_longjmp_test.c

@@ -5,13 +5,8 @@
 #include <setjmp.h>
 #include <testing.h>
 
-// Clang doesn't provide setjmp()/longjmp() support on some architectures.
-#if !defined(__aarch64__) && !defined(__riscv)
-
 TEST(setjmp_longjmp, example) {
   jmp_buf jmp;
   while (setjmp(jmp) != 123)
     longjmp(jmp, 123);
 }
-
-#endif

src/libc/setjmp/sigsetjmp_siglongjmp_test.c

@@ -5,13 +5,8 @@
 #include <setjmp.h>
 #include <testing.h>
 
-// Clang doesn't provide setjmp()/longjmp() support on some architectures.
-#if !defined(__aarch64__) && !defined(__riscv)
-
 TEST(sigsetjmp_siglongjmp, example) {
   sigjmp_buf jmp;
   while (sigsetjmp(jmp, 0) != 123)
     siglongjmp(jmp, 123);
 }
-
-#endif