src/libcompiler_builtins/src/x86.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(windows, target_env = "gnu", not(feature = "mangled-names")))]
  12 #[naked]
  13 #[no_mangle]
  14 pub unsafe fn ___chkstk_ms() {
  15     asm!("
  16         push   %ecx
  17         push   %eax
  18         cmp    $$0x1000,%eax
  19         lea    12(%esp),%ecx
  20         jb     1f
  21     2:
  22         sub    $$0x1000,%ecx
  23         test   %ecx,(%ecx)
  24         sub    $$0x1000,%eax
  25         cmp    $$0x1000,%eax
  26         ja     2b
  27     1:
  28         sub    %eax,%ecx
  29         test   %ecx,(%ecx)
  30         pop    %eax
  31         pop    %ecx
  32         ret" ::: "memory" : "volatile");
  33     intrinsics::unreachable();
  34 }
  35
  36 // FIXME: __alloca should be an alias to __chkstk
  37 #[cfg(all(windows, target_env = "gnu", not(feature = "mangled-names")))]
  38 #[naked]
  39 #[no_mangle]
  40 pub unsafe fn __alloca() {
  41     asm!("jmp ___chkstk   // Jump to ___chkstk since fallthrough may be unreliable"
  42          ::: "memory" : "volatile");
  43     intrinsics::unreachable();
  44 }
  45
  46 #[cfg(all(windows, target_env = "gnu", not(feature = "mangled-names")))]
  47 #[naked]
  48 #[no_mangle]
  49 pub unsafe fn ___chkstk() {
  50     asm!("
  51         push   %ecx
  52         cmp    $$0x1000,%eax
  53         lea    8(%esp),%ecx     // esp before calling this routine -> ecx
  54         jb     1f
  55     2:
  56         sub    $$0x1000,%ecx
  57         test   %ecx,(%ecx)
  58         sub    $$0x1000,%eax
  59         cmp    $$0x1000,%eax
  60         ja     2b
  61     1:
  62         sub    %eax,%ecx
  63         test   %ecx,(%ecx)
  64
  65         lea    4(%esp),%eax     // load pointer to the return address into eax
  66         mov    %ecx,%esp        // install the new top of stack pointer into esp
  67         mov    -4(%eax),%ecx    // restore ecx
  68         push   (%eax)           // push return address onto the stack
  69         sub    %esp,%eax        // restore the original value in eax
  70         ret" ::: "memory" : "volatile");
  71     intrinsics::unreachable();
  72 }