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runtime: steal space for stack barrier tracking from stack

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The stack barrier code will need a bookkeeping structure to keep track
of the overwritten return PCs. This commit introduces and allocates
this structure, but does not yet use the structure.

We don't want to allocate space for this structure during garbage
collection, so this commit allocates it along with the allocation of
the corresponding stack. However, we can't do a regular allocation in
newstack because mallocgc may itself grow the stack (which would lead
to a recursive allocation). Hence, this commit makes the bookkeeping
structure part of the stack allocation itself by stealing the
necessary space from the top of the stack allocation. Since the size
of this bookkeeping structure is logarithmic in the size of the stack,
this has minimal impact on stack behavior.

Change-Id: Ia14408be06aafa9ca4867f4e70bddb3fe0e96665
Reviewed-on: https://go-review.googlesource.com/10313
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Austin Clements 2015-05-20 16:16:04 -04:00
parent e610c25df0
commit 3f6e69aca5
5 changed files with 65 additions and 6 deletions
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6
src/runtime/proc1.go
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@ -2157,7 +2157,7 @@ func malg(stacksize int32) *g {
if stacksize >= 0 {
stacksize = round2(_StackSystem + stacksize)
systemstack(func() {
newg.stack = stackalloc(uint32(stacksize))
newg.stack, newg.stkbar = stackalloc(uint32(stacksize))
})
newg.stackguard0 = newg.stack.lo + _StackGuard
newg.stackguard1 = ^uintptr(0)
@ -2285,6 +2285,8 @@ func gfput(_p_ *p, gp *g) {
gp.stack.lo = 0
gp.stack.hi = 0
gp.stackguard0 = 0
gp.stkbar = nil
gp.stkbarPos = 0
}
gp.schedlink.set(_p_.gfree)
@ -2328,7 +2330,7 @@ retry:
if gp.stack.lo == 0 {
// Stack was deallocated in gfput. Allocate a new one.
systemstack(func() {
gp.stack = stackalloc(_FixedStack)
gp.stack, gp.stkbar = stackalloc(_FixedStack)
})
gp.stackguard0 = gp.stack.lo + _StackGuard
gp.stackAlloc = _FixedStack