libc/src/setjmp/x86_64/setjmp.cpp

   1 //===-- Implementation of setjmp ------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/__support/common.h"
  10 #include "src/setjmp/setjmp_impl.h"
  11
  12 #if !defined(LIBC_TARGET_ARCH_IS_X86_64)
  13 #error "Invalid file include"
  14 #endif
  15
  16 namespace __llvm_libc {
  17
  18 LLVM_LIBC_FUNCTION(int, setjmp, (__jmp_buf * buf)) {
  19   register __UINT64_TYPE__ rbx __asm__("rbx");
  20   register __UINT64_TYPE__ r12 __asm__("r12");
  21   register __UINT64_TYPE__ r13 __asm__("r13");
  22   register __UINT64_TYPE__ r14 __asm__("r14");
  23   register __UINT64_TYPE__ r15 __asm__("r15");
  24
  25   // We want to store the register values as is. So, we will suppress the
  26   // compiler warnings about the uninitialized variables declared above.
  27 #pragma GCC diagnostic push
  28 #pragma GCC diagnostic ignored "-Wuninitialized"
  29   LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->rbx) : "r"(rbx) :);
  30   LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->r12) : "r"(r12) :);
  31   LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->r13) : "r"(r13) :);
  32   LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->r14) : "r"(r14) :);
  33   LIBC_INLINE_ASM("mov %1, %0\n\t" : "=m"(buf->r15) : "r"(r15) :);
  34 #pragma GCC diagnostic pop
  35
  36   // We want the rbp of the caller, which is what __builtin_frame_address(1)
  37   // should return. But, compilers generate a warning that calling
  38   // __builtin_frame_address with non-zero argument is unsafe. So, we use
  39   // the knowledge of the x86_64 ABI to fetch the callers rbp. As per the ABI,
  40   // the rbp of the caller is pushed on to the stack and then new top is saved
  41   // in this function's rbp. So, we fetch it from location at which this
  42   // functions's rbp is pointing.
  43   buf->rbp = *reinterpret_cast<__UINTPTR_TYPE__ *>(__builtin_frame_address(0));
  44
  45   // The callers stack address is exactly 2 pointer widths ahead of the current
  46   // frame pointer - between the current frame pointer and the rsp of the caller
  47   // are the return address (pushed by the x86_64 call instruction) and the
  48   // previous stack pointer as required by the x86_64 ABI.
  49   // The stack pointer is ahead because the stack grows down on x86_64.
  50   buf->rsp = reinterpret_cast<__UINTPTR_TYPE__>(__builtin_frame_address(0)) +
  51              sizeof(__UINTPTR_TYPE__) * 2;
  52   buf->rip = reinterpret_cast<__UINTPTR_TYPE__>(__builtin_return_address(0));
  53   return 0;
  54 }
  55
  56 } // namespace __llvm_libc