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cmd/cgo: enable reproducible builds when LTO is enabled #53528

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49 changes: 49 additions & 0 deletions src/cmd/go/internal/work/exec.go
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
package work

import (
"bufio"
"bytes"
"context"
"crypto/sha256"
Expand Down Expand Up @@ -2508,6 +2509,38 @@ func (b *Builder) gfortran(a *Action, p *load.Package, workdir, out string, flag
return b.ccompile(a, p, out, flags, ffile, b.gfortranCmd(p.Dir, workdir))
}

// bareLineSymbols returns any C #line macros inserted by cmd/cgo with just a name and no path.
func bareLineSymbols(file string) ([][]byte, error) {
var symbols [][]byte
f, err := os.Open(file)
if err != nil {
return nil, err
}
defer f.Close()
bufr := bufio.NewReader(f)
for {
line, _, err := bufr.ReadLine()
if err == io.EOF {
break
} else if err != nil {
return nil, fmt.Errorf("failed to read line macros from cgo2.c file: %v", err)
}
if !bytes.HasPrefix(line, []byte("#line")) {
continue
}
s := bytes.Split(line, []byte(` `))
if len(s) != 3 {
continue
}
symbol := bytes.Trim(s[2], `"`)
if !bytes.HasPrefix(symbol, []byte("cgo")) {
continue
}
symbols = append(symbols, symbol)
}
return symbols, nil
}

// ccompile runs the given C or C++ compiler and creates an object from a single source file.
func (b *Builder) ccompile(a *Action, p *load.Package, outfile string, flags []string, file string, compiler []string) error {
file = mkAbs(p.Dir, file)
Expand Down Expand Up @@ -2548,6 +2581,22 @@ func (b *Builder) ccompile(a *Action, p *load.Package, outfile string, flags []s
if p, ok := a.nonGoOverlay[overlayPath]; ok {
overlayPath = p
}

// GCC embeds the working directory to bare symbols in line macros
// when LTO is used on cgo2.c files.
// See go.dev/issue/53528
if strings.HasSuffix(file, "cgo2.c") && !cfg.BuildN {
lineSymbols, err := bareLineSymbols(overlayPath)
if err != nil {
return err
}
// The complexity of checking for duplicate symbols isn't worth it
// as duplicate prefix-maps doesn't affect the output.
for _, line := range lineSymbols {
flags = append(flags, fmt.Sprintf("-fdebug-prefix-map=%s=/tmp/go-build/%s", line, line))
}
}

output, err := b.runOut(a, filepath.Dir(overlayPath), b.cCompilerEnv(), compiler, flags, "-o", outfile, "-c", filepath.Base(overlayPath))
if len(output) > 0 {
// On FreeBSD 11, when we pass -g to clang 3.8 it
Expand Down
33 changes: 33 additions & 0 deletions src/cmd/go/testdata/script/build_issue413974.txt
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
# Regression test for https://go.dev/issue/53528:
# cgo build should reproduce binaries with LTO enable

[!cgo] skip
[short] skip 'links cgo binaries'

env GOFLAGS=-ldflags=-linkmode=external
env CGO_CFLAGS=-flto

go build -o main.exe
mv main.exe main1.exe

env GOCACHE=$WORK${/}gocache
mkdir $GOCACHE
go build -o main.exe
mv main.exe main2.exe

cmp -q main2.exe main1.exe

-- go.mod --
module main

go 1.18
-- main.go --
package main

import "C"

var _ C.int

func main() {
println("Hello World")
}

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