[libc][RISCV] Add naked attribute to setjmp/longjmp (#100036)

We want to avoid any possibility that the compiler will insert a prologue/epilogue violating the calling contracts for these special functions, potentially clobbering registers that must be preserved. To do that they should be marked naked, as is already the case on ARM. See #87837 for further context.
llvm · Jul 23, 2024 · 05b586b · 05b586b
1 parent 5fc9502
commit 05b586b
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diff --git a/libc/src/setjmp/riscv/longjmp.cpp b/libc/src/setjmp/riscv/longjmp.cpp
@@ -30,6 +30,7 @@
 
 namespace LIBC_NAMESPACE_DECL {
 
+[[gnu::naked]]
 LLVM_LIBC_FUNCTION(void, longjmp, (__jmp_buf * buf, int val)) {
   LOAD(ra, buf->__pc);
   LOAD(s0, buf->__regs[0]);

diff --git a/libc/src/setjmp/riscv/setjmp.cpp b/libc/src/setjmp/riscv/setjmp.cpp
@@ -29,6 +29,7 @@
 
 namespace LIBC_NAMESPACE_DECL {
 
+[[gnu::naked]]
 LLVM_LIBC_FUNCTION(int, setjmp, (__jmp_buf * buf)) {
   STORE(ra, buf->__pc);
   STORE(s0, buf->__regs[0]);