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cmd/link/internal/ld: fix sort comparison

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Strictly speaking, the sort comparison was inconsistent
(and therefore invalid) for the sort-by-name case, if you had

	a size 0
	b size 1
	c size 0
	zerobase

That would result in the inconsistent comparison ordering:

	a < b (by name)
	b < c (by name)
	c < zerobase (by zerobase rule)
	zerobase < b (by zerobase rule)

This can't happen today because we only disable size-based
sort in a segment that has no zerobase symbol, but it's
confusing to reason through that, so clean up the code anyway.

Passes golang.org/x/tools/cmd/toolstash/buildall.

Change-Id: I21e4159cdedd2053952ba960530d1b0f28c6fb24
Reviewed-on: https://go-review.googlesource.com/c/go/+/625615
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Russ Cox 2024-10-30 19:23:47 -04:00
parent 7fff741016
commit 72801623cb
1 changed files with 12 additions and 11 deletions
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23
src/cmd/link/internal/ld/data.go
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@ -2240,12 +2240,12 @@ func (state *dodataState) dodataSect(ctxt *Link, symn sym.SymKind, syms []loader
// from input files. Both are type sym.SELFGOT, so in that case
// we skip size comparison and do the name comparison instead
// (conveniently, .got sorts before .toc).
checkSize := symn != sym.SELFGOT
sortBySize := symn != sym.SELFGOT
for k, s := range syms {
ss := ldr.SymSize(s)
sl[k] = symNameSize{sz: ss, sym: s}
if !checkSize {
if !sortBySize {
sl[k].name = ldr.SymName(s)
}
ds := int64(len(ldr.Data(s)))
@ -2286,15 +2286,16 @@ func (state *dodataState) dodataSect(ctxt *Link, symn sym.SymKind, syms []loader
return true
case sj == head, si == tail:
return false
// put zerobase right after all the zero-sized symbols,
// so zero-sized symbols have the same address as zerobase.
case si == zerobase:
return jsz != 0 // zerobase < nonzero-sized
case sj == zerobase:
return isz == 0 // 0-sized < zerobase
}
if checkSize {
if isz != jsz {
if sortBySize {
switch {
// put zerobase right after all the zero-sized symbols,
// so zero-sized symbols have the same address as zerobase.
case si == zerobase:
return jsz != 0 // zerobase < nonzero-sized, zerobase > zero-sized
case sj == zerobase:
return isz == 0 // 0-sized < zerobase, nonzero-sized > zerobase
case isz != jsz:
return isz < jsz
}
} else {
@ -2304,7 +2305,7 @@ func (state *dodataState) dodataSect(ctxt *Link, symn sym.SymKind, syms []loader
return iname < jname
}
}
return si < sj
return si < sj // break ties by symbol number
})
} else {
// PCLNTAB was built internally, and already has the proper order.