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[dev.link] cmd/link: handle multiple levels of overwrite

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Revamp the way that symbol overwrites are handled to deal with symbols
that are overwritten more than once (such as "_cgo_mmap"). The
scenario here is that a symbol can be overwritten twice, once during
preload, and then again when host objects are read during internal
linking. This can result in a situation where we have two entries in
the overwrite map, from X -> Y and then from Y -> Z. Rather than
search the overwrite map when adding new entries, add a helper routine
for querying the map that catches this situation and fixes it up.

Also with this patch is a couple of tweaks to the loader.Dump method
to insure that it can dump the entire global index space without
crashing due to odd overwrites (as in the scenario above).

Change-Id: Ib6c8a0e03e92fc2b57318001711b501eeaf12249
Reviewed-on: https://go-review.googlesource.com/c/go/+/212098
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
This commit is contained in:
Than McIntosh 2019-12-18 15:14:46 -05:00
parent 49e94f19f0
commit db48d45838
2 changed files with 81 additions and 17 deletions
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4
src/cmd/link/internal/loader/symbolbuilder.go
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@ -41,9 +41,7 @@ func (l *Loader) MakeSymbolUpdater(symIdx Sym) (*SymbolBuilder, Sym) {
if symIdx == 0 {
panic("can't update the null symbol")
}
if ov, ok := l.overwrite[symIdx]; ok {
symIdx = ov
}
symIdx = l.getOverwrite(symIdx)
if !l.IsExternal(symIdx) {
// Create a clone with the same name/version/kind etc.
symIdx = l.cloneToExternal(symIdx)