[libc] implement sigsetjmp for thumb/thumb2/armv7-a (#138147)

libc/config/linux/arm/entrypoints.txt

diff --git a/libc/config/linux/arm/entrypoints.txt b/libc/config/linux/arm/entrypoints.txt
index 1161ae2..fa62f4d 100644
--- a/libc/config/linux/arm/entrypoints.txt
+++ b/libc/config/linux/arm/entrypoints.txt
@@ -201,6 +201,8 @@
     # setjmp.h entrypoints
     libc.src.setjmp.longjmp
     libc.src.setjmp.setjmp
+    libc.src.setjmp.siglongjmp
+    libc.src.setjmp.sigsetjmp
   )
 endif()
 

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

diff --git a/libc/include/llvm-libc-types/jmp_buf.h b/libc/include/llvm-libc-types/jmp_buf.h
index 2fec35d..8a7d283 100644
--- a/libc/include/llvm-libc-types/jmp_buf.h
+++ b/libc/include/llvm-libc-types/jmp_buf.h
@@ -13,7 +13,7 @@
 // Issue: https://github.com/llvm/llvm-project/issues/136358
 #if defined(__linux__)
 #if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) ||        \
-    defined(__riscv)
+    defined(__arm__) || defined(__riscv)
 #define __LIBC_HAS_SIGJMP_BUF
 #endif
 #endif

libc/src/setjmp/arm/CMakeLists.txt

diff --git a/libc/src/setjmp/arm/CMakeLists.txt b/libc/src/setjmp/arm/CMakeLists.txt
index 55c80b0..77f8471 100644
--- a/libc/src/setjmp/arm/CMakeLists.txt
+++ b/libc/src/setjmp/arm/CMakeLists.txt
@@ -8,6 +8,22 @@
     libc.hdr.types.jmp_buf
 )
 
+if (TARGET libc.src.setjmp.sigsetjmp_epilogue)
+  add_entrypoint_object(
+    sigsetjmp
+    SRCS
+      sigsetjmp.cpp
+    HDRS
+      ../sigsetjmp.h
+    DEPENDS
+      libc.hdr.types.jmp_buf
+      libc.hdr.types.sigset_t
+      libc.hdr.offsetof_macros
+      libc.src.setjmp.sigsetjmp_epilogue
+      libc.src.setjmp.setjmp
+  )
+endif()
+
 add_entrypoint_object(
   longjmp
   SRCS

libc/src/setjmp/arm/sigsetjmp.cpp

diff --git a/libc/src/setjmp/arm/sigsetjmp.cpp b/libc/src/setjmp/arm/sigsetjmp.cpp
new file mode 100644
index 0000000..41c86bd
--- /dev/null
+++ b/libc/src/setjmp/arm/sigsetjmp.cpp
@@ -0,0 +1,65 @@
+//===-- Implementation of sigsetjmp ---------------------------------------===//
+//
+// 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/sigsetjmp.h"
+#include "hdr/offsetof_macros.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/setjmp/setjmp_impl.h"
+#include "src/setjmp/sigsetjmp_epilogue.h"
+
+namespace LIBC_NAMESPACE_DECL {
+[[gnu::naked]]
+LLVM_LIBC_FUNCTION(int, sigsetjmp, (sigjmp_buf buf)) {
+#if defined(__thumb__) && __ARM_ARCH_ISA_THUMB == 1
+  // Thumb1 does not support the high registers > r7 in stmia, so move them
+  // into lower GPRs first.
+  asm(R"(
+      tst r1, r1
+      bne .Ldosave
+      b %c[setjmp]
+.Ldosave:
+      str r4, [r0, #%c[extra]]
+      mov r4, lr
+      str r4, [r0, #%c[retaddr]]
+      mov r4, r0
+      bl %c[setjmp]
+      mov r1, r0
+      mov r0, r4
+      ldr r4, [r0, #%c[retaddr]]
+      mov lr, r4
+      ldr r4, [r0, #%c[extra]]
+      b %c[epilogue]
+  )" ::[retaddr] "i"(offsetof(__jmp_buf, sig_retaddr)),
+      [extra] "i"(offsetof(__jmp_buf, sig_extra)), [setjmp] "i"(setjmp),
+      [epilogue] "i"(sigsetjmp_epilogue)
+      : "r0", "r1", "r4");
+#else
+  // Some thumb2 linkers do not support conditional branch to PLT.
+  // We branch to local labels instead.
+  asm(R"(
+      tst r1, r1
+      bne .Ldosave
+      b %c[setjmp]
+.Ldosave:
+      str r4, [r0, #%c[extra]]
+      str lr, [r0, #%c[retaddr]]
+      mov r4, r0
+      bl %c[setjmp]
+      mov r1, r0
+      mov r0, r4
+      ldr lr, [r0, #%c[retaddr]]
+      ldr r4, [r0, #%c[extra]]
+      b %c[epilogue]
+  )" ::[retaddr] "i"(offsetof(__jmp_buf, sig_retaddr)),
+      [extra] "i"(offsetof(__jmp_buf, sig_extra)), [setjmp] "X"(setjmp),
+      [epilogue] "X"(sigsetjmp_epilogue)
+      : "r0", "r1", "r4");
+#endif
+}
+} // namespace LIBC_NAMESPACE_DECL