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-rw-r--r--src/pkg/runtime/stack.h113
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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 and on
- // Plan 9 because they do not use a separate stack.
-#ifdef GOOS_windows
- StackSystem = 512 * sizeof(uintptr),
-#else
-#ifdef GOOS_plan9
- // The size of the note handler frame varies among architectures,
- // but 512 bytes should be enough for every implementation.
- StackSystem = 512,
-#else
- StackSystem = 0,
-#endif // Plan 9
-#endif // Windows
-
- // The amount of extra stack to allocate beyond the size
- // needed for the single frame that triggered the split.
- StackExtra = 2048,
-
- // 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 = 8192,
- StackSystemRounded = StackSystem + (-StackSystem & (StackMin-1)),
- FixedStack = StackMin + StackSystemRounded,
-
- // Functions that need frames bigger than this use an extra
- // instruction to do the stack split check, to avoid overflow
- // in case SP - framesize wraps below zero.
- // This value can be no bigger than the size of the unmapped
- // space at zero.
- 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,
-
- // The assumed size of the top-of-stack data block.
- // The actual size can be smaller than this but cannot be larger.
- // Checked in proc.c's runtime.malg.
- StackTop = 88,
-};
-
-// Goroutine preemption request.
-// Stored into g->stackguard0 to cause split stack check failure.
-// Must be greater than any real sp.
-// 0xfffffade in hex.
-#define StackPreempt ((uint64)-1314)