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-rw-r--r--src/pkg/runtime/stack.h96
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diff --git a/src/pkg/runtime/stack.h b/src/pkg/runtime/stack.h
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-// Copyright 2011 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-/*
-Stack layout parameters.
-Included both by runtime (compiled via 6c) and linkers (compiled via gcc).
-
-The per-goroutine g->stackguard is set to point StackGuard bytes
-above the bottom of the stack. Each function compares its stack
-pointer against g->stackguard to check for overflow. To cut one
-instruction from the check sequence for functions with tiny frames,
-the stack is allowed to protrude StackSmall bytes below the stack
-guard. Functions with large frames don't bother with the check and
-always call morestack. The sequences are (for amd64, others are
-similar):
-
- guard = g->stackguard
- frame = function's stack frame size
- argsize = size of function arguments (call + return)
-
- stack frame size <= StackSmall:
- CMPQ guard, SP
- JHI 3(PC)
- MOVQ m->morearg, $(argsize << 32)
- CALL morestack(SB)
-
- stack frame size > StackSmall but < StackBig
- LEAQ (frame-StackSmall)(SP), R0
- CMPQ guard, R0
- JHI 3(PC)
- MOVQ m->morearg, $(argsize << 32)
- CALL morestack(SB)
-
- stack frame size >= StackBig:
- MOVQ m->morearg, $((argsize << 32) | frame)
- CALL morestack(SB)
-
-The bottom StackGuard - StackSmall bytes are important: there has
-to be enough room to execute functions that refuse to check for
-stack overflow, either because they need to be adjacent to the
-actual caller's frame (deferproc) or because they handle the imminent
-stack overflow (morestack).
-
-For example, deferproc might call malloc, which does one of the
-above checks (without allocating a full frame), which might trigger
-a call to morestack. This sequence needs to fit in the bottom
-section of the stack. On amd64, morestack's frame is 40 bytes, and
-deferproc's frame is 56 bytes. That fits well within the
-StackGuard - StackSmall = 128 bytes at the bottom.
-The linkers explore all possible call traces involving non-splitting
-functions to make sure that this limit cannot be violated.
- */
-
-enum {
- // StackSystem is a number of additional bytes to add
- // to each stack below the usual guard area for OS-specific
- // purposes like signal handling. Used on Windows because
- // it does not use a separate stack.
-#ifdef __WINDOWS__
- StackSystem = 2048,
-#else
- StackSystem = 0,
-#endif
-
- // The amount of extra stack to allocate beyond the size
- // needed for the single frame that triggered the split.
- StackExtra = 1024,
-
- // The minimum stack segment size to allocate.
- // If the amount needed for the splitting frame + StackExtra
- // is less than this number, the stack will have this size instead.
- StackMin = 4096,
-
- // Functions that need frames bigger than this call morestack
- // unconditionally. That is, on entry to a function it is assumed
- // that the amount of space available in the current stack segment
- // couldn't possibly be bigger than StackBig. If stack segments
- // do run with more space than StackBig, the space may not be
- // used efficiently. As a result, StackBig should not be significantly
- // smaller than StackMin or StackExtra.
- StackBig = 4096,
-
- // The stack guard is a pointer this many bytes above the
- // bottom of the stack.
- StackGuard = 256 + StackSystem,
-
- // After a stack split check the SP is allowed to be this
- // many bytes below the stack guard. This saves an instruction
- // in the checking sequence for tiny frames.
- StackSmall = 128,
-
- // The maximum number of bytes that a chain of NOSPLIT
- // functions can use.
- StackLimit = StackGuard - StackSystem - StackSmall,
-};