From 24e9707cbfa6b1ed6abdd4b11f9ddaf3aac5ad88 Mon Sep 17 00:00:00 2001
From: Ian Lance Taylor <iant@golang.org>
Date: Tue, 25 May 2021 16:31:41 -0700
Subject: [PATCH] cmd/link, cmd/cgo: support -flto in CFLAGS
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>
---
diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index ae61725..a73e998 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -1638,6 +1638,8 @@
c = append(c, "-maix64")
c = append(c, "-mcmodel=large")
}
+ // disable LTO so we get an object whose symbols we can read
+ c = append(c, "-fno-lto")
c = append(c, "-") //read input from standard input
return c
}
diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 8c31d5b..94152f4 100644
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -168,8 +168,18 @@
if *gccgo {
fmt.Fprintf(fc, "extern byte *%s;\n", n.C)
} else {
- fmt.Fprintf(fm, "extern char %s[];\n", n.C)
- fmt.Fprintf(fm, "void *_cgohack_%s = %s;\n\n", n.C, n.C)
+ // Force a reference to all symbols so that
+ // the external linker will add DT_NEEDED
+ // entries as needed on ELF systems.
+ // Treat function variables differently
+ // to avoid type confict errors from LTO
+ // (Link Time Optimization).
+ if n.Kind == "fpvar" {
+ fmt.Fprintf(fm, "extern void %s();\n", n.C)
+ } else {
+ fmt.Fprintf(fm, "extern char %s[];\n", n.C)
+ fmt.Fprintf(fm, "void *_cgohack_%s = %s;\n\n", n.C, n.C)
+ }
fmt.Fprintf(fgo2, "//go:linkname __cgo_%s %s\n", n.C, n.C)
fmt.Fprintf(fgo2, "//go:cgo_import_static %s\n", n.C)
fmt.Fprintf(fgo2, "var __cgo_%s byte\n", n.C)
@@ -1042,7 +1052,7 @@
fmt.Fprintf(fgo2, "//go:cgo_export_static _cgoexp%s_%s\n", cPrefix, exp.ExpName)
fmt.Fprintf(fgo2, "func _cgoexp%s_%s(a *%s) {\n", cPrefix, exp.ExpName, gotype)
- fmt.Fprintf(fm, "int _cgoexp%s_%s;\n", cPrefix, exp.ExpName)
+ fmt.Fprintf(fm, "void _cgoexp%s_%s(void* p){}\n", cPrefix, exp.ExpName)
if gccResult != "void" {
// Write results back to frame.
diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go
index 50bf80b..bc49c6d 100644
--- a/src/cmd/dist/test.go
+++ b/src/cmd/dist/test.go
@@ -722,14 +722,29 @@
},
})
if t.hasCxx() {
- t.tests = append(t.tests, distTest{
- name: "swig_callback",
- heading: "../misc/swig/callback",
- fn: func(dt *distTest) error {
- t.addCmd(dt, "misc/swig/callback", t.goTest())
- return nil
+ t.tests = append(t.tests,
+ distTest{
+ name: "swig_callback",
+ heading: "../misc/swig/callback",
+ fn: func(dt *distTest) error {
+ t.addCmd(dt, "misc/swig/callback", t.goTest())
+ return nil
+ },
},
- })
+ distTest{
+ name: "swig_callback_lto",
+ heading: "../misc/swig/callback",
+ fn: func(dt *distTest) error {
+ cmd := t.addCmd(dt, "misc/swig/callback", t.goTest())
+ cmd.Env = append(os.Environ(),
+ "CGO_CFLAGS=-flto",
+ "CGO_CXXFLAGS=-flto",
+ "CGO_LDFLAGS=-flto",
+ )
+ return nil
+ },
+ },
+ )
}
}
}
diff --git a/src/cmd/go/testdata/script/cgo_lto2_issue43830.txt b/src/cmd/go/testdata/script/cgo_lto2_issue43830.txt
new file mode 100644
index 0000000..e2483ba
--- /dev/null
+++ b/src/cmd/go/testdata/script/cgo_lto2_issue43830.txt
@@ -0,0 +1,33 @@
+# tests golang.org/issue/43830
+
+[!cgo] skip 'skipping test without cgo'
+[openbsd] env CC='clang'
+[openbsd] [!exec:clang] skip 'skipping test without clang present'
+[!openbsd] env CC='gcc'
+[!openbsd] [!exec:gcc] skip 'skipping test without gcc present'
+
+env CGO_CFLAGS='-Wno-ignored-optimization-argument -flto -ffat-lto-objects'
+
+go build main.go
+
+-- main.go --
+
+package main
+
+import "fmt"
+
+// #include "hello.h"
+import "C"
+
+func main() {
+ hello := C.hello
+ fmt.Printf("%v\n", hello)
+}
+
+-- hello.h --
+
+#include <stdio.h>
+
+void hello(void) {
+ printf("hello\n");
+}
diff --git a/src/cmd/go/testdata/script/cgo_lto_issue43830.txt b/src/cmd/go/testdata/script/cgo_lto_issue43830.txt
new file mode 100644
index 0000000..06ab2f3
--- /dev/null
+++ b/src/cmd/go/testdata/script/cgo_lto_issue43830.txt
@@ -0,0 +1,39 @@
+# tests golang.org/issue/43830
+
+[!cgo] skip 'skipping test without cgo'
+[openbsd] env CC='clang'
+[openbsd] [!exec:clang] skip 'skipping test without clang present'
+[!openbsd] env CC='gcc'
+[!openbsd] [!exec:gcc] skip 'skipping test without gcc present'
+
+env CGO_CFLAGS='-Wno-ignored-optimization-argument -flto -ffat-lto-objects'
+
+go build main.go add.go
+
+-- main.go --
+
+package main
+
+/*
+int c_add(int a, int b) {
+ return myadd(a, b);
+}
+*/
+import "C"
+
+func main() {
+ println(C.c_add(1, 2))
+}
+
+-- add.go --
+
+package main
+
+import "C"
+
+/* test */
+
+//export myadd
+func myadd(a C.int, b C.int) C.int {
+ return a + b
+}
diff --git a/src/cmd/link/internal/ld/ar.go b/src/cmd/link/internal/ld/ar.go
index 22f53a4..23915f9 100644
--- a/src/cmd/link/internal/ld/ar.go
+++ b/src/cmd/link/internal/ld/ar.go
@@ -124,6 +124,10 @@
libgcc := sym.Library{Pkg: "libgcc"}
h := ldobj(ctxt, f, &libgcc, l, pname, name)
+ if h.ld == nil {
+ Errorf(nil, "%s unrecognized object file at offset %d", name, off)
+ continue
+ }
f.MustSeek(h.off, 0)
h.ld(ctxt, f, h.pkg, h.length, h.pn)
}
diff --git a/src/cmd/link/internal/ld/config.go b/src/cmd/link/internal/ld/config.go
index ae0d752..20f1d0b 100644
--- a/src/cmd/link/internal/ld/config.go
+++ b/src/cmd/link/internal/ld/config.go
@@ -241,6 +241,10 @@
return true, "dynamically linking with a shared library"
}
+ if unknownObjFormat {
+ return true, "some input objects have an unrecognized file format"
+ }
+
return false, ""
}
@@ -248,7 +252,7 @@
//
// It is called after flags are processed and inputs are processed,
// so the ctxt.LinkMode variable has an initial value from the -linkmode
-// flag and the iscgo externalobj variables are set.
+// flag and the iscgo, externalobj, and unknownObjFormat variables are set.
func determineLinkMode(ctxt *Link) {
extNeeded, extReason := mustLinkExternal(ctxt)
via := ""
diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index e8f001b..644faeb 100644
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -343,10 +343,16 @@
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 @@
}
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 @@
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 {