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

[James Y Knight via libc-commits]

================
@@ -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:
----------------
jyknight wrote:

Does this public symbol need to be conditioned on `LIBC_COPT_PUBLIC_PACKAGING`?

Maybe something like:
```
#ifdef LIBC_COPT_PUBLIC_PACKAGING
#define LIBC_ASM_PUBLIC_ALIAS(alias, orig) \
  .globl  alias \
  .type   alias, at function \
  .set alias, orig
#else
#define LIBC_ASM_PUBLIC_ALIAS(alias, orig)
#endif

LIBC_ASM_PUBLIC_ALIAS(setjmp, LIBC_NAMESPACE_setjmp)
```
(Note: in the above `.size` isn't needed, as it gets copied over automatically)

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