[libc][arm] implement setjmp/longjmp

Note: our baremetal arm configuration compiles this as
`--target=arm-none-eabi`, so this code is built in -marm mode. It could be
smaller with `--target=armv7-none-eabi -mthumb`. The assembler is valid ARMv5,
or THUMB2, but not THUMB(1). Unclear yet if we need to support THUMB(1); may
depend on whether downstream users are using llvm-libc's cmake.

Author: nickdesaulniers

libc/config/baremetal/arm/entrypoints.txt

@@ -26,6 +26,10 @@ set(TARGET_LIBC_ENTRYPOINTS
     # errno.h entrypoints
     libc.src.errno.errno
 
+    # setjmp.h entrypoints
+    libc.src.setjmp.longjmp
+    libc.src.setjmp.setjmp
+
     # string.h entrypoints
     libc.src.string.bcmp
     libc.src.string.bcopy

libc/config/baremetal/arm/headers.txt

@@ -1,13 +1,14 @@
 set(TARGET_PUBLIC_HEADERS
     libc.include.assert
     libc.include.ctype
-    libc.include.fenv
     libc.include.errno
+    libc.include.fenv
     libc.include.float
-    libc.include.stdint
     libc.include.inttypes
     libc.include.math
+    libc.include.setjmp
     libc.include.stdfix
+    libc.include.stdint
     libc.include.stdio
     libc.include.stdlib
     libc.include.string

libc/config/linux/arm/entrypoints.txt

@@ -20,6 +20,10 @@ set(TARGET_LIBC_ENTRYPOINTS
     # errno.h entrypoints
     libc.src.errno.errno
 
+    # setjmp.h entrypoints
+    libc.src.setjmp.longjmp
+    libc.src.setjmp.setjmp
+
     # string.h entrypoints
     libc.src.string.bcmp
     libc.src.string.bcopy

libc/config/linux/arm/headers.txt

@@ -1,19 +1,20 @@
 set(TARGET_PUBLIC_HEADERS
     libc.include.ctype
-    libc.include.fenv
     libc.include.errno
+    libc.include.fenv
     libc.include.float
-    libc.include.stdint
     libc.include.inttypes
     libc.include.math
-    libc.include.stdckdint
+    libc.include.search
+    libc.include.setjmp
     libc.include.stdbit
+    libc.include.stdckdint
+    libc.include.stdint
     libc.include.stdlib
     libc.include.string
     libc.include.strings
-    libc.include.search
-    libc.include.wchar
     libc.include.uchar
+    libc.include.wchar
 
     # Disabled due to epoll_wait syscalls not being available on this platform.
     # libc.include.sys_epoll

libc/include/llvm-libc-types/jmp_buf.h

@@ -32,6 +32,9 @@ typedef struct {
 #elif defined(__riscv_float_abi_single)
 #error "__jmp_buf not available for your target architecture."
 #endif
+#elif defined(__arm__)
+  // r4, r5, r6, r7, r8, r9, r10, r11, r12, lr
+  long opaque [10];
 #else
 #error "__jmp_buf not available for your target architecture."
 #endif

libc/include/setjmp.h.def

@@ -10,6 +10,7 @@
 #define LLVM_LIBC_SETJMP_H
 
 #include "__llvm-libc-common.h"
+#include "llvm-libc-types/jmp_buf.h"
 
 %%public_api()
 

libc/src/setjmp/arm/CMakeLists.txt

@@ -0,0 +1,19 @@
+add_entrypoint_object(
+  setjmp
+  SRCS
+    setjmp.cpp
+  HDRS
+    ../setjmp_impl.h
+  DEPENDS
+    libc.include.setjmp
+)
+
+add_entrypoint_object(
+  longjmp
+  SRCS
+    longjmp.cpp
+  HDRS
+    ../longjmp.h
+  DEPENDS
+    libc.include.setjmp
+)

libc/src/setjmp/arm/longjmp.cpp

@@ -0,0 +1,31 @@
+
+//===-- Implementation of longjmp -----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/setjmp/longjmp.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/properties/architectures.h"
+
+#if !defined(LIBC_TARGET_ARCH_IS_ARM)
+#error "Invalid file include"
+#endif
+
+namespace LIBC_NAMESPACE {
+
+[[gnu::naked]]
+LLVM_LIBC_FUNCTION(void, longjmp, (__jmp_buf * buf, int val)) {
+  asm("ldm.w r0!, {r4, r5, r6, r7, r8, r9, r10, r11, r12, lr}\n\t"
+      "mov sp, r12\n\t"
+      "movs r0, r1\n\t"
+      "it eq\n\t"
+      "moveq r0, 1\n\t"
+      "bx lr"
+  );
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/setjmp/arm/setjmp.cpp

@@ -0,0 +1,27 @@
+//===-- Implementation of setjmp ------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/common.h"
+#include "src/setjmp/setjmp_impl.h"
+
+#if !defined(LIBC_TARGET_ARCH_IS_ARM)
+#error "Invalid file include"
+#endif
+
+namespace LIBC_NAMESPACE {
+
+[[gnu::naked]]
+LLVM_LIBC_FUNCTION(int, setjmp, (__jmp_buf * buf)) {
+  asm("mov r12, sp\n\t"
+      "stm.w r0!, {r4, r5, r6, r7, r8, r9, r10, r11, r12, lr}\n\t"
+      "mov.w r0, 0\n\t"
+      "bx lr\n\t"
+  );
+}
+
+} // namespace LIBC_NAMESPACE