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cmd/link: only include the version info and export data in ABI hash

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Previously the "ABI hash" for a package (used to determine if a loaded shared
library has the ABI expected by its loader) was the hash of the entire
__.PKGDEF file. But that means it depends on the build ID generated by the go
tool for the package, which means that if a file is added (even a .c or .h
file!) to the package, the ABI changes, perhaps uncessarily.

Fixes #19920

Change-Id: If919481e1a03afb350c8a9c7a0666bb90ee90270
Reviewed-on: https://go-review.googlesource.com/40401
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Michael Hudson-Doyle 2017-04-12 16:08:46 +12:00
parent 94b6011c78
commit 533ed967c6
2 changed files with 37 additions and 4 deletions
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29
src/cmd/link/internal/ld/lib.go
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@ -720,10 +720,35 @@ func genhash(ctxt *Link, lib *Library) {
}
h := sha1.New()
if _, err := io.CopyN(h, f, atolwhex(arhdr.size)); err != nil {
Errorf(nil, "bad read of %s for hash generation: %v", lib.File, err)
// To compute the hash of a package, we hash the first line of
// __.PKGDEF (which contains the toolchain version and any
// GOEXPERIMENT flags) and the export data (which is between
// the first two occurences of "\n$$").
pkgDefBytes := make([]byte, atolwhex(arhdr.size))
_, err = io.ReadFull(f, pkgDefBytes)
if err != nil {
Errorf(nil, "%s: error reading package data: %v", lib.File, err)
return
}
firstEOL := bytes.Index(pkgDefBytes, []byte("\n"))
if firstEOL < 0 {
Errorf(nil, "cannot parse package data of %s for hash generation, no newline found", lib.File)
return
}
firstDoubleDollar := bytes.Index(pkgDefBytes, []byte("\n$$"))
if firstDoubleDollar < 0 {
Errorf(nil, "cannot parse package data of %s for hash generation, no \\n$$ found", lib.File)
return
}
secondDoubleDollar := bytes.Index(pkgDefBytes[firstDoubleDollar+1:], []byte("\n$$"))
if secondDoubleDollar < 0 {
Errorf(nil, "cannot parse package data of %s for hash generation, only one \\n$$ found", lib.File)
return
}
h.Write(pkgDefBytes[0:firstEOL])
h.Write(pkgDefBytes[firstDoubleDollar : firstDoubleDollar+secondDoubleDollar])
lib.hash = hex.EncodeToString(h.Sum(nil))
}