[libc-commits] [libc] [libc][setjmp][x86] implement setjmp in terms of out of line asm (PR #88157)

[James Y Knight via libc-commits]

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@@ -0,0 +1,50 @@
+//===-- Implementation of setjmp --------------------------------*- ASM -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#define paste(ns) _ZN22 ## ns ## 6setjmpEP9__jmp_buf
+#define expand(x) paste(x)
+#define LIBC_NAMESPACE_setjump expand(LIBC_NAMESPACE)
+// aka _ZN22__llvm_libc_19_0_0_git6setjmpEP9__jmp_buf
+// aka __llvm_libc_19_0_0_git::setjmp(__jmp_buf*)
+
+// Brittle! Changing the layout of __jmp_buf will break this!
+#define RBX_OFFSET 0
+#define RBP_OFFSET 8
+#define R12_OFFSET 16
+#define R13_OFFSET 24
+#define R14_OFFSET 32
+#define R15_OFFSET 40
+#define RSP_OFFSET 48
+#define RIP_OFFSET 56
+
+.global setjump
+.global LIBC_NAMESPACE_setjump
+
+.type setjump, @function
+.type LIBC_NAMESPACE_setjump, @function
+
+setjump:
+LIBC_NAMESPACE_setjump:
+
+  mov %rbx, RBX_OFFSET(%rdi)
+  mov %rbp, RBP_OFFSET(%rdi)
+  mov %r12, R12_OFFSET(%rdi)
+  mov %r13, R13_OFFSET(%rdi)
+  mov %r14, R14_OFFSET(%rdi)
+  mov %r15, R15_OFFSET(%rdi)
+  lea 8(%rsp), %rax
+  mov %rax, RSP_OFFSET(%rdi)
+  mov (%rsp), %rax
+  mov %rax, RIP_OFFSET(%rdi)
+  xor %eax, %eax
+  ret
+
+.size setjump, . - setjump
+.size LIBC_NAMESPACE_setjump, . - LIBC_NAMESPACE_setjump
+
+.section .note.GNU-stack, "", @progbits
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jyknight wrote:

Should use `NO_EXEC_STACK_DIRECTIVE` macro (as e.g. defined in compiler-rt's assembly.h file) instead of hard-coding, since GNU-stack isn't used/useful on all platforms.

https://github.com/llvm/llvm-project/pull/88157