[libc][i386] setjmp/longjmp

[nickdesaulniers]

Link: #93709

[llvmbot]

@llvm/pr-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

Changes

Link: #93709

---

Full diff: https://github.com/llvm/llvm-project/pull/112437.diff

4 Files Affected:

• (modified) libc/include/llvm-libc-types/jmp_buf.h (+7)
• (modified) libc/src/setjmp/longjmp.h (+1)
• (modified) libc/src/setjmp/x86_64/longjmp.cpp (+31-2)
• (modified) libc/src/setjmp/x86_64/setjmp.cpp (+30-1)

diff --git a/libc/include/llvm-libc-types/jmp_buf.h b/libc/include/llvm-libc-types/jmp_buf.h
index 60e033c6c65a95..f246e6491cf554 100644
--- a/libc/include/llvm-libc-types/jmp_buf.h
+++ b/libc/include/llvm-libc-types/jmp_buf.h
@@ -19,6 +19,13 @@ typedef struct {
   __UINT64_TYPE__ r15;
   __UINTPTR_TYPE__ rsp;
   __UINTPTR_TYPE__ rip;
+#elif defined(__i386__)
+  long ebx;
+  long esi;
+  long edi;
+  long ebp;
+  long esp;
+  long eip;
 #elif defined(__riscv)
   /* Program counter.  */
   long int __pc;
diff --git a/libc/src/setjmp/longjmp.h b/libc/src/setjmp/longjmp.h
index 7cb12b3392ae16..e8d6985f44ee4d 100644
--- a/libc/src/setjmp/longjmp.h
+++ b/libc/src/setjmp/longjmp.h
@@ -14,6 +14,7 @@
 
 namespace LIBC_NAMESPACE_DECL {
 
+[[noreturn]]
 void longjmp(jmp_buf buf, int val);
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/setjmp/x86_64/longjmp.cpp b/libc/src/setjmp/x86_64/longjmp.cpp
index d4b55565cb2187..f27e5f055d6f99 100644
--- a/libc/src/setjmp/x86_64/longjmp.cpp
+++ b/libc/src/setjmp/x86_64/longjmp.cpp
@@ -6,16 +6,44 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "src/setjmp/longjmp.h"
+#include "include/llvm-libc-macros/offsetof-macro.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
+#include "src/setjmp/longjmp.h"
 
-#if !defined(LIBC_TARGET_ARCH_IS_X86_64)
+#if !defined(LIBC_TARGET_ARCH_IS_X86)
 #error "Invalid file include"
 #endif
 
 namespace LIBC_NAMESPACE_DECL {
 
+#ifdef __i386__
+[[noreturn]]
+LLVM_LIBC_FUNCTION(void, longjmp, (jmp_buf, int val)) {
+  asm(R"(
+      mov 4(%%esp), %%edx
+
+      mov %c[ebx](%%edx), %%ebx
+      mov %c[esi](%%edx), %%esi
+      mov %c[edi](%%edx), %%edi
+      mov %c[ebp](%%edx), %%ebp
+      mov %c[esp](%%edx), %%esp
+
+      jmp *%c[eip](%%edx)
+      )"
+      ::
+      [ebx] "i"(offsetof(__jmp_buf, ebx)),
+      [esi] "i"(offsetof(__jmp_buf, esi)),
+      [edi] "i"(offsetof(__jmp_buf, edi)),
+      [ebp] "i"(offsetof(__jmp_buf, ebp)),
+      [esp] "i"(offsetof(__jmp_buf, esp)),
+      [eip] "i"(offsetof(__jmp_buf, eip)),
+      [val] "a"(val == 0 ? 1 : val) :
+      "edx");
+  __builtin_unreachable();
+}
+#else
+[[noreturn]]
 LLVM_LIBC_FUNCTION(void, longjmp, (jmp_buf buf, int val)) {
   register __UINT64_TYPE__ rbx __asm__("rbx");
   register __UINT64_TYPE__ rbp __asm__("rbp");
@@ -41,5 +69,6 @@ LLVM_LIBC_FUNCTION(void, longjmp, (jmp_buf buf, int val)) {
   LIBC_INLINE_ASM("mov %1, %0\n\t" : "=r"(rsp) : "m"(buf->rsp) :);
   LIBC_INLINE_ASM("jmp *%0\n\t" : : "m"(buf->rip));
 }
+#endif
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/setjmp/x86_64/setjmp.cpp b/libc/src/setjmp/x86_64/setjmp.cpp
index f6e82642edd7da..90532c5654b33b 100644
--- a/libc/src/setjmp/x86_64/setjmp.cpp
+++ b/libc/src/setjmp/x86_64/setjmp.cpp
@@ -11,12 +11,40 @@
 #include "src/__support/macros/config.h"
 #include "src/setjmp/setjmp_impl.h"
 
-#if !defined(LIBC_TARGET_ARCH_IS_X86_64)
+#if !defined(LIBC_TARGET_ARCH_IS_X86)
 #error "Invalid file include"
 #endif
 
 namespace LIBC_NAMESPACE_DECL {
 
+#ifdef __i386__
+[[gnu::naked]]
+LLVM_LIBC_FUNCTION(int, setjmp, (jmp_buf buf)) {
+  asm(R"(
+      mov 4(%%esp), %%eax
+
+      mov %%ebx, %c[ebx](%%eax)
+      mov %%esi, %c[esi](%%eax)
+      mov %%edi, %c[edi](%%eax)
+      mov %%ebp, %c[ebp](%%eax)
+
+      lea 4(%%esp), %%ecx
+      mov %%ecx, %c[esp](%%eax)
+
+      mov (%%esp), %%ecx
+      mov %%ecx, %c[eip](%%eax)
+
+      xorl %%eax, %%eax
+      retl)" ::
+      [ebx] "i"(offsetof(__jmp_buf, ebx)),
+      [esi] "i"(offsetof(__jmp_buf, esi)),
+      [edi] "i"(offsetof(__jmp_buf, edi)),
+      [ebp] "i"(offsetof(__jmp_buf, ebp)),
+      [esp] "i"(offsetof(__jmp_buf, esp)),
+      [eip] "i"(offsetof(__jmp_buf, eip))
+      : "eax", "ecx");
+}
+#else
 [[gnu::naked]]
 LLVM_LIBC_FUNCTION(int, setjmp, (jmp_buf buf)) {
   asm(R"(
@@ -41,5 +69,6 @@ LLVM_LIBC_FUNCTION(int, setjmp, (jmp_buf buf)) {
       [rip] "i"(offsetof(__jmp_buf, rip))
       : "rax");
 }
+#endif
 
 } // namespace LIBC_NAMESPACE_DECL

[github-actions]

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

[nickdesaulniers]

I'll land #112443 first, then revisit this in that style.

[nickdesaulniers]

ok, I've converted longjmp to be a naked fn using offsetof. I'll send a patch to fix up x86_64 in a distinct PR. Ready for rereview.