vendor/compiler_builtins/src/x86_64.rs

   1 #![allow(unused_imports)]
   2
   3 use core::intrinsics;
   4
   5 // NOTE These functions are implemented using assembly because they using a custom
   6 // calling convention which can't be implemented using a normal Rust function
   7
   8 // NOTE These functions are never mangled as they are not tested against compiler-rt
   9 // and mangling ___chkstk would break the `jmp ___chkstk` instruction in __alloca
  10
  11 #[cfg(all(
  12     windows,
  13     target_env = "gnu",
  14     not(feature = "no-asm"),
  15     not(feature = "mangled-names")
  16 ))]
  17 #[naked]
  18 #[no_mangle]
  19 pub unsafe fn ___chkstk_ms() {
  20     llvm_asm!("
  21         push   %rcx
  22         push   %rax
  23         cmp    $$0x1000,%rax
  24         lea    24(%rsp),%rcx
  25         jb     1f
  26     2:
  27         sub    $$0x1000,%rcx
  28         test   %rcx,(%rcx)
  29         sub    $$0x1000,%rax
  30         cmp    $$0x1000,%rax
  31         ja     2b
  32     1:
  33         sub    %rax,%rcx
  34         test   %rcx,(%rcx)
  35         pop    %rax
  36         pop    %rcx
  37         ret" ::: "memory" : "volatile");
  38     intrinsics::unreachable();
  39 }
  40
  41 #[cfg(all(
  42     windows,
  43     target_env = "gnu",
  44     not(feature = "no-asm"),
  45     not(feature = "mangled-names")
  46 ))]
  47 #[naked]
  48 #[no_mangle]
  49 pub unsafe fn __alloca() {
  50     llvm_asm!("mov    %rcx,%rax  // x64 _alloca is a normal function with parameter in rcx
  51           jmp    ___chkstk  // Jump to ___chkstk since fallthrough may be unreliable"
  52          ::: "memory" : "volatile");
  53     intrinsics::unreachable();
  54 }
  55
  56 #[cfg(all(
  57     windows,
  58     target_env = "gnu",
  59     not(feature = "no-asm"),
  60     not(feature = "mangled-names")
  61 ))]
  62 #[naked]
  63 #[no_mangle]
  64 pub unsafe fn ___chkstk() {
  65     llvm_asm!(
  66         "
  67         push   %rcx
  68         cmp    $$0x1000,%rax
  69         lea    16(%rsp),%rcx  // rsp before calling this routine -> rcx
  70         jb     1f
  71     2:
  72         sub    $$0x1000,%rcx
  73         test   %rcx,(%rcx)
  74         sub    $$0x1000,%rax
  75         cmp    $$0x1000,%rax
  76         ja     2b
  77     1:
  78         sub    %rax,%rcx
  79         test   %rcx,(%rcx)
  80
  81         lea    8(%rsp),%rax   // load pointer to the return address into rax
  82         mov    %rcx,%rsp      // install the new top of stack pointer into rsp
  83         mov    -8(%rax),%rcx  // restore rcx
  84         push   (%rax)         // push return address onto the stack
  85         sub    %rsp,%rax      // restore the original value in rax
  86         ret"
  87         ::: "memory" : "volatile"
  88     );
  89     intrinsics::unreachable();
  90 }
  91
  92 // HACK(https://github.com/rust-lang/rust/issues/62785): x86_64-unknown-uefi needs special LLVM
  93 // support unless we emit the _fltused
  94 #[no_mangle]
  95 #[used]
  96 #[cfg(target_os = "uefi")]
  97 static _fltused: i32 = 0;