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runtime: decouple stack bounds and stack allocation size

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Currently the runtime assumes that the allocation for the stack is
exactly [stack.lo, stack.hi). We're about to steal a small part of
this allocation for per-stack GC metadata. To prepare for this, this
commit adds a field to the G for the allocated size of the stack.
With this change, stack.lo and stack.hi continue to act as the true
bounds on the stack, but are no longer also used as the bounds on the
stack allocation.

(I also tried this the other way around, where stack.lo and stack.hi
remained the allocation bounds and I introduced a new top of stack.
However, there are far more places that assume stack.hi is the true
top of the stack than there are places that assume it's the top of the
allocation.)

Change-Id: Ifa9d956753be53d286d09cbc73d47fb34a18c0c6
Reviewed-on: https://go-review.googlesource.com/10312
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Austin Clements 2015-05-20 15:29:53 -04:00
parent c02b8911d8
commit e610c25df0
3 changed files with 20 additions and 11 deletions
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1
src/runtime/runtime2.go
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@ -216,6 +216,7 @@ type g struct {
_panic *_panic // innermost panic - offset known to liblink
_defer *_defer // innermost defer
stackAlloc uintptr // stack allocation is [stack.lo,stack.lo+stackAlloc)
sched gobuf
syscallsp uintptr // if status==Gsyscall, syscallsp = sched.sp to use during gc
syscallpc uintptr // if status==Gsyscall, syscallpc = sched.pc to use during gc