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Update DeallocationStack for Windows context switch #15032

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Merged
straight-shoota merged 1 commit into from
Sep 26, 2024
Merged

Update DeallocationStack for Windows context switch #15032

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17 changes: 11 additions & 6 deletions src/fiber/context/x86_64-microsoft.cr
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Original file line number Diff line number Diff line change
Expand Up @@ -4,19 +4,20 @@ class Fiber
# :nodoc:
def makecontext(stack_ptr, fiber_main) : Nil
# A great explanation on stack contexts for win32:
# https://cfsamson.gitbook.io/green-threads-explained-in-200-lines-of-rust/supporting-windows
# https://web.archive.org/web/20220527113808/https://cfsamson.gitbook.io/green-threads-explained-in-200-lines-of-rust/supporting-windows

# 8 registers + 2 qwords for NT_TIB + 1 parameter + 10 128bit XMM registers
@context.stack_top = (stack_ptr - (11 + 10*2)).as(Void*)
# 8 registers + 3 qwords for NT_TIB + 1 parameter + 10 128bit XMM registers
@context.stack_top = (stack_ptr - (12 + 10*2)).as(Void*)
@context.resumable = 1

stack_ptr[0] = fiber_main.pointer # %rbx: Initial `resume` will `ret` to this address
stack_ptr[-1] = self.as(Void*) # %rcx: puts `self` as first argument for `fiber_main`

# The following two values are stored in the Thread Information Block (NT_TIB)
# The following three values are stored in the Thread Information Block (NT_TIB)
# and are used by Windows to track the current stack limits
stack_ptr[-2] = @stack # %gs:0x10: Stack Limit
stack_ptr[-3] = @stack_bottom # %gs:0x08: Stack Base
stack_ptr[-2] = @stack # %gs:0x1478: Win32 DeallocationStack
stack_ptr[-3] = @stack # %gs:0x10: Stack Limit
stack_ptr[-4] = @stack_bottom # %gs:0x08: Stack Base
end

# :nodoc:
Expand All @@ -27,6 +28,7 @@ class Fiber
# %rcx , %rdx
asm("
pushq %rcx
pushq %gs:0x1478 // Thread Information Block: Win32 DeallocationStack
pushq %gs:0x10 // Thread Information Block: Stack Limit
pushq %gs:0x08 // Thread Information Block: Stack Base
pushq %rdi // push 1st argument (because of initial resume)
Expand Down Expand Up @@ -73,13 +75,15 @@ class Fiber
popq %rdi // pop 1st argument (for initial resume)
popq %gs:0x08
popq %gs:0x10
popq %gs:0x1478
popq %rcx
")
{% else %}
# On LLVM < 9.0 using the previous code emits some additional
# instructions that breaks the context switching.
asm("
pushq %rcx
pushq %gs:0x1478 // Thread Information Block: Win32 DeallocationStack
pushq %gs:0x10 // Thread Information Block: Stack Limit
pushq %gs:0x08 // Thread Information Block: Stack Base
pushq %rdi // push 1st argument (because of initial resume)
Expand Down Expand Up @@ -126,6 +130,7 @@ class Fiber
popq %rdi // pop 1st argument (for initial resume)
popq %gs:0x08
popq %gs:0x10
popq %gs:0x1478
popq %rcx
" :: "r"(current_context), "r"(new_context))
{% end %}
Expand Down