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cmd/link, cmd/cgo: support -flto in CFLAGS

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The linker now accepts unrecognized object files in external linking mode.
These objects will simply be passed to the external linker.
This permits using -flto which can generate pure byte code objects,
whose symbol table the linker does not know how to read.

The cgo tool now passes -fno-lto when generating objects whose symbols
it needs to read. The cgo tool now emits matching types in different
objects, so that the lto linker does not report a mismatch.

This is based on https://golang.org/cl/293290 by Derek Parker.

For #43505
Fixes #43830
Fixes #46295

Change-Id: I6787de213417466784ddef5af8899e453b4ae1ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/322614
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
This commit is contained in:
Ian Lance Taylor 2021-05-25 16:31:41 -07:00
parent 272552275f
commit 24e9707cbf
8 changed files with 140 additions and 15 deletions
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26
src/cmd/link/internal/ld/lib.go
View file

@ -343,10 +343,16 @@ var (
const pkgdef = "__.PKGDEF"
var (
// Set if we see an object compiled by the host compiler that is not
// from a package that is known to support internal linking mode.
// externalobj is set to true if we see an object compiled by
// the host compiler that is not from a package that is known
// to support internal linking mode.
externalobj = false
theline string
// unknownObjFormat is set to true if we see an object whose
// format we don't recognize.
unknownObjFormat = false
theline string
)
func Lflag(ctxt *Link, arg string) {
@ -1065,6 +1071,10 @@ func hostobjs(ctxt *Link) {
}
f.MustSeek(h.off, 0)
if h.ld == nil {
Errorf(nil, "%s: unrecognized object file format", h.pn)
continue
}
h.ld(ctxt, f, h.pkg, h.length, h.pn)
f.Close()
}
@ -1855,6 +1865,14 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
return ldhostobj(ldxcoff, ctxt.HeadType, f, pkg, length, pn, file)
}
if c1 != 'g' || c2 != 'o' || c3 != ' ' || c4 != 'o' {
// An unrecognized object is just passed to the external linker.
// If we try to read symbols from this object, we will
// report an error at that time.
unknownObjFormat = true
return ldhostobj(nil, ctxt.HeadType, f, pkg, length, pn, file)
}
/* check the header */
line, err := f.ReadString('\n')
if err != nil {
@ -1874,7 +1892,7 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
return nil
}
Errorf(nil, "%s: not an object file: @%d %02x%02x%02x%02x", pn, start, c1, c2, c3, c4)
Errorf(nil, "%s: not an object file: @%d %q", pn, start, line)
return nil
}