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cmd/link: fix nosplit stack overflow checks

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The nosplit stack overflow checks were confused about morestack.
The comment about not having correct SP information at the call
to morestack was true, but that was a real bug, not something to
work around. I fixed that problem in CL 12144. With that fixed,
no need to special-case morestack in the way done here.

This cleanup and simplification of the code was the first step
to fixing a bug that happened when I started working on the
arm64 frame size adjustments, but the cleanup was sufficient
to make the bug go away.

For #9880.

Change-Id: I16b69a5c16b6b8cb4090295d3029c42d606e3b9b
Reviewed-on: https://go-review.googlesource.com/12846
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Russ Cox 2015-07-29 15:07:35 -04:00
parent 421220571d
commit 767e065809
1 changed files with 12 additions and 35 deletions
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47
src/cmd/link/internal/ld/lib.go
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@ -1465,10 +1465,7 @@ type Chain struct {
limit int // limit on entry to sym
}
var (
morestack *LSym
newstack *LSym
)
var morestack *LSym
// TODO: Record enough information in new object files to
// allow stack checks here.
@ -1488,7 +1485,6 @@ func dostkcheck() {
var ch Chain
morestack = Linklookup(Ctxt, "runtime.morestack", 0)
newstack = Linklookup(Ctxt, "runtime.newstack", 0)
// Every splitting function ensures that there are at least StackLimit
// bytes available below SP when the splitting prologue finishes.
@ -1533,7 +1529,8 @@ func stkcheck(up *Chain, depth int) int {
// Don't duplicate work: only need to consider each
// function at top of safe zone once.
if limit == obj.StackLimit-callsize() {
top := limit == obj.StackLimit-callsize()
if top {
if s.Stkcheck != 0 {
return 0
}
@ -1571,39 +1568,21 @@ func stkcheck(up *Chain, depth int) int {
var ch Chain
ch.up = up
// Check for a call to morestack anywhere and treat it
// as occurring at function entry.
// The decision about whether to call morestack occurs
// in the prolog, but the call site is near the end
// of the function on some architectures.
// This is needed because the stack check is flow-insensitive,
// so it incorrectly thinks the call to morestack happens wherever it shows up.
// This check will be wrong if there are any hand-inserted calls to morestack.
// There are not any now, nor should there ever be.
for _, r := range s.R {
if r.Sym == nil || !strings.HasPrefix(r.Sym.Name, "runtime.morestack") {
continue
}
// Ignore non-calls to morestack, such as the jump to morestack
// found in the implementation of morestack_noctxt.
switch r.Type {
default:
continue
case obj.R_CALL, obj.R_CALLARM, obj.R_CALLARM64, obj.R_CALLPOWER:
}
if s.Nosplit == 0 {
// Ensure we have enough stack to call morestack.
ch.limit = limit - callsize()
ch.sym = r.Sym
ch.sym = morestack
if stkcheck(&ch, depth+1) < 0 {
return -1
}
// Bump up the limit.
if !top {
return 0
}
// Raise limit to allow frame.
limit = int(obj.StackLimit + s.Locals)
if haslinkregister() {
limit += Thearch.Regsize
}
break // there can be only one
}
// Walk through sp adjustments in function, consuming relocs.
@ -1628,11 +1607,6 @@ func stkcheck(up *Chain, depth int) int {
switch r.Type {
// Direct call.
case obj.R_CALL, obj.R_CALLARM, obj.R_CALLARM64, obj.R_CALLPOWER:
// We handled calls to morestack already.
if strings.HasPrefix(r.Sym.Name, "runtime.morestack") {
continue
}
ch.limit = int(int32(limit) - pcsp.value - int32(callsize()))
ch.sym = r.Sym
if stkcheck(&ch, depth+1) < 0 {
@ -1670,6 +1644,9 @@ func stkprint(ch *Chain, limit int) {
if ch.sym != nil {
name = ch.sym.Name
if ch.sym.Nosplit != 0 {
name += " (nosplit)"
}
} else {
name = "function pointer"
}