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cmd/{compile,link}: fix bug in map.zero handling

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In CL 326211 a change was made to switch "go.map.zero" symbols from
non-pkg DUPOK symbols to hashed symbols. The intent of this change was
ensure that in cases where there are multiple competing go.map.zero
symbols feeding into a link, the largest map.zero symbol is selected.
The change was buggy, however, and resulted in duplicate symbols in
the final binary (see bug cited below for details). This duplication
was relatively benign for linux/ELF, but causes duplicate definition
errors on Windows.

This patch switches "go.map.zero" symbols back from hashed symbols to
non-pkg DUPOK symbols, and updates the relevant code in the loader to
ensure that we do the right thing when there are multiple competing
DUPOK symbols with different sizes.

Fixes #47185.

Change-Id: I8aeb910c65827f5380144d07646006ba553c9251
Reviewed-on: https://go-review.googlesource.com/c/go/+/334930
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Than McIntosh 2021-07-15 16:29:36 -04:00
parent a66190ecee
commit 49402bee36
5 changed files with 121 additions and 1 deletions
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9
src/cmd/link/internal/loader/loader.go
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@ -459,6 +459,15 @@ func (st *loadState) addSym(name string, ver int, r *oReader, li uint32, kind in
if l.flags&FlagStrictDups != 0 {
l.checkdup(name, r, li, oldi)
}
// Fix for issue #47185 -- given two dupok symbols with
// different sizes, favor symbol with larger size. See
// also issue #46653.
szdup := l.SymSize(oldi)
sz := int64(r.Sym(li).Siz())
if szdup < sz {
// new symbol overwrites old symbol.
l.objSyms[oldi] = objSym{r.objidx, li}
}
return oldi
}
oldr, oldli := l.toLocal(oldi)