[libc-commits] [libc] [libc] fortify jmp buffer for x86-64 (PR #112769)

[Nick Desaulniers via libc-commits]

================
@@ -11,32 +11,82 @@
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
 
+#if LIBC_COPT_SETJMP_FORTIFICATION
+#include "src/setjmp/checksum.h"
+#endif
+
 #if !defined(LIBC_TARGET_ARCH_IS_X86_64)
 #error "Invalid file include"
 #endif
 
 namespace LIBC_NAMESPACE_DECL {
 
-[[gnu::naked]]
-LLVM_LIBC_FUNCTION(void, longjmp, (jmp_buf, int)) {
-  asm(R"(
-      cmpl $0x1, %%esi
-      adcl $0x0, %%esi
-      movq %%rsi, %%rax
-
-      movq %c[rbx](%%rdi), %%rbx
-      movq %c[rbp](%%rdi), %%rbp
-      movq %c[r12](%%rdi), %%r12
-      movq %c[r13](%%rdi), %%r13
-      movq %c[r14](%%rdi), %%r14
-      movq %c[r15](%%rdi), %%r15
-      movq %c[rsp](%%rdi), %%rsp
-      jmpq *%c[rip](%%rdi)
-      )" ::[rbx] "i"(offsetof(__jmp_buf, rbx)),
-      [rbp] "i"(offsetof(__jmp_buf, rbp)), [r12] "i"(offsetof(__jmp_buf, r12)),
-      [r13] "i"(offsetof(__jmp_buf, r13)), [r14] "i"(offsetof(__jmp_buf, r14)),
-      [r15] "i"(offsetof(__jmp_buf, r15)), [rsp] "i"(offsetof(__jmp_buf, rsp)),
-      [rip] "i"(offsetof(__jmp_buf, rip)));
+#define CALCULATE_RETURN_VALUE()                                               \
+  "cmpl $0x1, %%esi\n\t"                                                       \
+  "adcl $0x0, %%esi\n\t"                                                       \
+  "movq %%rsi, %%rax\n\t"
+
+#if LIBC_COPT_SETJMP_FORTIFICATION
+#include "src/setjmp/x86_64/checksum.def"
+
+// clang-format off
+#define RESTORE_REG(DST)                                                       \
+  "movq %c[" #DST "](%%rdi), %%rax\n\t"                                        \
+  "movq %%rax, %%" #DST "\n\t"                                                 \
+  "xor %[mask], %%" #DST "\n\t"                                                \
+  ACCUMULATE_CHECKSUM()
+
+#define RESTORE_RIP()                                                          \
+  "movq %c[rip](%%rdi), %%rax\n\t"                                             \
+  "xor %%rax, %[mask]\n\t"                                                     \
+  ACCUMULATE_CHECKSUM()                                                        \
+  "cmp %c[__chksum](%%rdi), %%rdx\n\t"                                         \
----------------
nickdesaulniers wrote:

why `%%rdx`? Is there a symbolic name we should be using instead?

https://github.com/llvm/llvm-project/pull/112769