[libc] fix -Wmissing-attributes in setjmp

[nickdesaulniers]

Fixes:

llvm-project/libc/src/setjmp/x86_64/setjmp.cpp:21:25: error: ‘int
__llvm_libc_19_0_0_git::setjmp(__jmp_buf*)’ specifies less restrictive
attribute than its target ‘int
__llvm_libc_19_0_0_git::__setjmp_impl__(__jmp_buf*)’: ‘nothrow’
[-Werror=missing-attributes]
   21 | LLVM_LIBC_FUNCTION(int, setjmp, (__jmp_buf * buf)) {
      |                         ^~~~~~

observed in the GCC build by manually expanding LLVM_LIBC_FUNCTION to add
gnu::nothrow to the alias.

We probably need to revisit adding nothrow throughout our declarations, so
there is probably a better way to clean this up in the future.

Link: #88054

[llvmbot]

@llvm/pr-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

Changes

Fixes:

llvm-project/libc/src/setjmp/x86_64/setjmp.cpp:21:25: error: ‘int
__llvm_libc_19_0_0_git::setjmp(__jmp_buf*)’ specifies less restrictive
attribute than its target ‘int
__llvm_libc_19_0_0_git::__setjmp_impl__(__jmp_buf*)’: ‘nothrow’
[-Werror=missing-attributes]
   21 | LLVM_LIBC_FUNCTION(int, setjmp, (__jmp_buf * buf)) {
      |                         ^~~~~~

observed in the GCC build by manually expanding LLVM_LIBC_FUNCTION to add
gnu::nothrow to the alias.

We probably need to revisit adding nothrow throughout our declarations, so
there is probably a better way to clean this up in the future.

Link: #88054

---

Full diff: https://github.com/llvm/llvm-project/pull/112415.diff

2 Files Affected:

• (modified) libc/src/setjmp/setjmp_impl.h (+1)
• (modified) libc/src/setjmp/x86_64/setjmp.cpp (+7-2)

diff --git a/libc/src/setjmp/setjmp_impl.h b/libc/src/setjmp/setjmp_impl.h
index 4175a7397ae187..a9f330d4722e10 100644
--- a/libc/src/setjmp/setjmp_impl.h
+++ b/libc/src/setjmp/setjmp_impl.h
@@ -16,6 +16,7 @@
 
 namespace LIBC_NAMESPACE_DECL {
 
+[[gnu::nothrow]]
 int setjmp(jmp_buf buf);
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/setjmp/x86_64/setjmp.cpp b/libc/src/setjmp/x86_64/setjmp.cpp
index c9ca578fb1e6db..7854132a83583c 100644
--- a/libc/src/setjmp/x86_64/setjmp.cpp
+++ b/libc/src/setjmp/x86_64/setjmp.cpp
@@ -17,8 +17,13 @@
 
 namespace LIBC_NAMESPACE_DECL {
 
-[[gnu::naked]]
-LLVM_LIBC_FUNCTION(int, setjmp, (__jmp_buf * buf)) {
+LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::setjmp) __setjmp_impl__ __asm__("setjmp");
+
+decltype(LIBC_NAMESPACE::setjmp) setjmp [[gnu::alias("setjmp"), gnu::nothrow]];
+
+[[gnu::naked, gnu::nothrow]]
+int __setjmp_impl__ (__jmp_buf *buf) {
+
   asm(R"(
       mov %%rbx, %c[rbx](%%rdi)
       mov %%rbp, %c[rbp](%%rdi)

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[nickdesaulniers]

It seems that naked functions are implicitly nothrow in GCC: https://godbolt.org/z/3Yv1ae5rv