[libc][AArch64] Add an AArch64 setjmp/longjmp.

libc/config/config.json

@@ -82,5 +82,11 @@
       "value": "LIBC_QSORT_QUICK_SORT",
       "doc": "Configures sorting algorithm for qsort and qsort_r. Values accepted are LIBC_QSORT_QUICK_SORT, LIBC_QSORT_HEAP_SORT."
     }
+  },
+  "setjmp": {
+    "LIBC_CONF_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER": {
+      "value": true,
+      "doc": "Make setjmp save the value of x18, and longjmp restore it. The AArch64 ABI delegates this register to platform ABIs, which can choose whether to make it caller-saved."
+    }
   }
 }

libc/config/linux/aarch64/entrypoints.txt

@@ -722,6 +722,10 @@ if(LLVM_LIBC_FULL_BUILD)
     # sched.h entrypoints
     libc.src.sched.__sched_getcpucount
 
+    # setjmp.h entrypoints
+    libc.src.setjmp.longjmp
+    libc.src.setjmp.setjmp
+
     # stdio.h entrypoints
     libc.src.stdio.clearerr
     libc.src.stdio.clearerr_unlocked

libc/docs/configure.rst

@@ -47,6 +47,8 @@ to learn about the defaults for your platform and target.
 * **"scanf" options**
     - ``LIBC_CONF_SCANF_DISABLE_FLOAT``: Disable parsing floating point values in scanf and friends.
     - ``LIBC_CONF_SCANF_DISABLE_INDEX_MODE``: Disable index mode in the scanf format string.
+* **"setjmp" options**
+    - ``LIBC_CONF_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER``: Make setjmp save the value of x18, and longjmp restore it. The AArch64 ABI delegates this register to platform ABIs, which can choose whether to make it caller-saved.
 * **"string" options**
     - ``LIBC_CONF_MEMSET_X86_USE_SOFTWARE_PREFETCHING``: Inserts prefetch for write instructions (PREFETCHW) for memset on x86 to recover performance when hardware prefetcher is disabled.
     - ``LIBC_CONF_STRING_UNSAFE_WIDE_READ``: Read more than a byte at a time to perform byte-string operations like strlen.

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

@@ -35,6 +35,11 @@ typedef struct {
 #elif defined(__arm__)
   // r4, r5, r6, r7, r8, r9, r10, r11, r12, lr
   long opaque[10];
+#elif defined(__aarch64__)
+  long opaque[14]; // x19-x29, lr, sp, optional x18
+#if __ARM_FP
+  long fopaque[8]; // d8-d15
+#endif
 #else
 #error "__jmp_buf not available for your target architecture."
 #endif

libc/src/setjmp/aarch64/CMakeLists.txt

@@ -0,0 +1,28 @@
+if(LIBC_CONF_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER)
+  list(APPEND setjmp_config_options "-DLIBC_COPT_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER")
+endif()
+if(setjmp_config_options)
+  list(PREPEND setjmp_config_options "COMPILE_OPTIONS")
+endif()
+
+add_entrypoint_object(
+  setjmp
+  SRCS
+    setjmp.cpp
+  HDRS
+    ../setjmp_impl.h
+  DEPENDS
+    libc.include.setjmp
+  ${setjmp_config_options}
+)
+
+add_entrypoint_object(
+  longjmp
+  SRCS
+    longjmp.cpp
+  HDRS
+    ../longjmp.h
+  DEPENDS
+    libc.include.setjmp
+  ${setjmp_config_options}
+)

libc/src/setjmp/aarch64/longjmp.cpp

@@ -0,0 +1,90 @@
+//===-- Implementation of longjmp for AArch64 -----------------------------===//
+//
+// 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/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+// TODO: if MTE stack tagging is in use (-fsanitize=memtag-stack), we need to
+// iterate over the region between the old and new values of sp, using STG or
+// ST2G instructions to clear the memory tags on the invalidated region of the
+// stack. But this requires a means of finding out that we're in that mode, and
+// as far as I can see there isn't currently a predefined macro for that.
+//
+// (__ARM_FEATURE_MEMORY_TAGGING only indicates whether the target architecture
+// supports the MTE instructions, not whether the compiler is configured to use
+// them.)
+
+[[gnu::naked]] LLVM_LIBC_FUNCTION(void, longjmp, (__jmp_buf * buf, int val)) {
+  // If BTI branch protection is in use, the compiler will automatically insert
+  // a BTI here, so we don't need to make any extra effort to do so.
+
+  // If PAC branch protection is in use, there's no need to sign the return
+  // address at the start of longjmp, because we're not going to use it anyway!
+
+  asm(
+      // Reload the callee-saved GPRs, including fp and lr.
+      R"(
+        ldp x19, x20, [x0,  #0*16]
+        ldp x21, x22, [x0,  #1*16]
+        ldp x23, x24, [x0,  #2*16]
+        ldp x25, x26, [x0,  #3*16]
+        ldp x27, x28, [x0,  #4*16]
+        ldp x29, x30, [x0,  #5*16]
+      )"
+
+#if LIBC_COPT_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER
+      // Reload the stack pointer, and the platform register x18.
+      R"(
+        ldp x2,  x18, [x0,  #6*16]
+        mov sp, x2
+      )"
+#else
+      // Reload just the stack pointer.
+      R"(
+        ldr x2,       [x0,  #6*16]
+        mov sp, x2
+      )"
+#endif
+
+#if __ARM_FP
+      // Reload the callee-saved FP registers.
+      R"(
+        ldp d8,  d9,  [x0,  #7*16]
+        ldp d10, d11, [x0,  #8*16]
+        ldp d12, d13, [x0,  #9*16]
+        ldp d14, d15, [x0, #10*16]
+      )"
+#endif
+
+      // Calculate the return value.
+      R"(
+        cmp w1, #0
+        cinc w0, w1, eq
+      )"
+
+#if __ARM_FEATURE_PAC_DEFAULT & 1
+      // Authenticate the return address using the PAC A key.
+      R"(
+        autiasp
+      )"
+#elif __ARM_FEATURE_PAC_DEFAULT & 2
+      // Authenticate the return address using the PAC B key.
+      R"(
+        autibsp
+      )"
+#endif
+
+      R"(
+        ret
+      )");
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/setjmp/aarch64/setjmp.cpp

@@ -0,0 +1,93 @@
+//===-- Implementation of setjmp for AArch64 ------------------------------===//
+//
+// 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/__support/macros/config.h"
+#include "src/setjmp/setjmp_impl.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+[[gnu::naked]] LLVM_LIBC_FUNCTION(int, setjmp, (__jmp_buf * buf)) {
+  // If BTI branch protection is in use, the compiler will automatically insert
+  // a BTI here, so we don't need to make any extra effort to do so.
+
+  asm(
+#if __ARM_FEATURE_PAC_DEFAULT & 1
+      // Sign the return address using the PAC A key.
+      R"(
+        paciasp
+      )"
+#elif __ARM_FEATURE_PAC_DEFAULT & 2
+      // Sign the return address using the PAC B key.
+      R"(
+        pacibsp
+      )"
+#endif
+
+      // Store all the callee-saved GPRs, including fp (x29) and also lr (x30).
+      // Of course lr isn't normally callee-saved (the call instruction itself
+      // can't help clobbering it), but we certainly need to save it for this
+      // purpose.
+      R"(
+        stp x19, x20, [x0,  #0*16]
+        stp x21, x22, [x0,  #1*16]
+        stp x23, x24, [x0,  #2*16]
+        stp x25, x26, [x0,  #3*16]
+        stp x27, x28, [x0,  #4*16]
+        stp x29, x30, [x0,  #5*16]
+      )"
+
+#if LIBC_COPT_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER
+      // Store the stack pointer, and the platform register x18.
+      R"(
+        add x1, sp, #0
+        stp x1, x18,  [x0,  #6*16]
+      )"
+#else
+      // Store just the stack pointer.
+      R"(
+        add x1, sp, #0
+        str x1,       [x0,  #6*16]
+      )"
+#endif
+
+#if __ARM_FP
+      // Store the callee-saved FP registers. AAPCS64 only requires the low 64
+      // bits of v8-v15 to be preserved, i.e. each of d8,...,d15.
+      R"(
+        stp d8,  d9,  [x0,  #7*16]
+        stp d10, d11, [x0,  #8*16]
+        stp d12, d13, [x0,  #9*16]
+        stp d14, d15, [x0, #10*16]
+      )"
+#endif
+
+      // Set up return value of zero.
+      R"(
+        mov x0, #0
+      )"
+
+#if (__ARM_FEATURE_PAC_DEFAULT & 7) == 5
+      // Authenticate the return address using the PAC A key, since the
+      // compilation options ask for PAC protection even on leaf functions.
+      R"(
+        autiasp
+      )"
+#elif (__ARM_FEATURE_PAC_DEFAULT & 7) == 6
+      // Same, but using the PAC B key.
+      R"(
+        autibsp
+      )"
+#endif
+
+      R"(
+        ret
+      )");
+}
+
+} // namespace LIBC_NAMESPACE_DECL