From 47db69e20ed66fb62b01affd83d829654b829893 Mon Sep 17 00:00:00 2001
From: Matt Madison <matt@madison.systems>
Date: Mon, 19 Feb 2018 08:50:59 -0800
Subject: [PATCH] cmd/go: make content-based hash generation less pedantic

Go 1.10's build tool now uses content-based hashes to
determine when something should be built or re-built.
This same mechanism is used to maintain a built-artifact
cache for speeding up builds.

However, the hashes it generates include information that
doesn't work well with OE, nor with using a shared runtime
library.

First, it embeds path names to source files, unless
building within GOROOT.  This prevents the building
of a package in GOPATH for later staging into GOROOT.

This patch adds support for the environment variable
GOPATH_OMIT_IN_ACTIONID.  If present, path name
embedding is disabled.

Second, if cgo is enabled, the build ID for cgo-related
packages will include the current value of the environment
variables for invoking the compiler (CC, CXX, FC) and
any CGO_xxFLAGS variables.  Only if the settings used
during a compilation exactly match, character for character,
the values used for compiling runtime/cgo or any other
cgo-enabled package being imported, will the tool
decide that the imported package is up-to-date.

This is done to help ensure correctness, but is overly
simplistic and effectively prevents the reuse of built
artifacts that use cgo (or shared runtime, which includes
runtime/cgo).

This patch filters out all compiler flags except those
beginning with '-m'.  The default behavior can be restored
by setting the CGO_PEDANTIC environment variable.

Upstream-Status: Inappropriate [OE specific]

Signed-off-by: Matt Madison <matt@madison.systems>

---
 src/cmd/go/internal/envcmd/env.go |  2 +-
 src/cmd/go/internal/work/exec.go  | 63 ++++++++++++++++++++++---------
 2 files changed, 46 insertions(+), 19 deletions(-)

diff --git a/src/cmd/go/internal/envcmd/env.go b/src/cmd/go/internal/envcmd/env.go
index cedbfbf..5763a0d 100644
--- a/src/cmd/go/internal/envcmd/env.go
+++ b/src/cmd/go/internal/envcmd/env.go
@@ -128,7 +128,7 @@ func ExtraEnvVars() []cfg.EnvVar {
 func ExtraEnvVarsCostly() []cfg.EnvVar {
 	var b work.Builder
 	b.Init()
-	cppflags, cflags, cxxflags, fflags, ldflags, err := b.CFlags(&load.Package{})
+	cppflags, cflags, cxxflags, fflags, ldflags, err := b.CFlags(&load.Package{}, false)
 	if err != nil {
 		// Should not happen - b.CFlags was given an empty package.
 		fmt.Fprintf(os.Stderr, "go: invalid cflags: %v\n", err)
diff --git a/src/cmd/go/internal/work/exec.go b/src/cmd/go/internal/work/exec.go
index 12e1527..e41bfac 100644
--- a/src/cmd/go/internal/work/exec.go
+++ b/src/cmd/go/internal/work/exec.go
@@ -174,6 +174,8 @@ func (b *Builder) Do(root *Action) {
 	wg.Wait()
 }
 
+var omitGopath = os.Getenv("GOPATH_OMIT_IN_ACTIONID") != ""
+
 // buildActionID computes the action ID for a build action.
 func (b *Builder) buildActionID(a *Action) cache.ActionID {
 	p := a.Package
@@ -190,7 +192,7 @@ func (b *Builder) buildActionID(a *Action) cache.ActionID {
 	// but it does not hide the exact value of $GOPATH.
 	// Include the full dir in that case.
 	// Assume b.WorkDir is being trimmed properly.
-	if !p.Goroot && !strings.HasPrefix(p.Dir, b.WorkDir) {
+	if !p.Goroot && !omitGopath && !strings.HasPrefix(p.Dir, b.WorkDir) {
 		fmt.Fprintf(h, "dir %s\n", p.Dir)
 	}
 	fmt.Fprintf(h, "goos %s goarch %s\n", cfg.Goos, cfg.Goarch)
@@ -201,13 +203,13 @@ func (b *Builder) buildActionID(a *Action) cache.ActionID {
 	}
 	if len(p.CgoFiles)+len(p.SwigFiles) > 0 {
 		fmt.Fprintf(h, "cgo %q\n", b.toolID("cgo"))
-		cppflags, cflags, cxxflags, fflags, ldflags, _ := b.CFlags(p)
-		fmt.Fprintf(h, "CC=%q %q %q %q\n", b.ccExe(), cppflags, cflags, ldflags)
+		cppflags, cflags, cxxflags, fflags, ldflags, _ := b.CFlags(p, true)
+		fmt.Fprintf(h, "CC=%q %q %q %q\n", b.ccExe(true), cppflags, cflags, ldflags)
 		if len(p.CXXFiles)+len(p.SwigFiles) > 0 {
-			fmt.Fprintf(h, "CXX=%q %q\n", b.cxxExe(), cxxflags)
+			fmt.Fprintf(h, "CXX=%q %q\n", b.cxxExe(true), cxxflags)
 		}
 		if len(p.FFiles) > 0 {
-			fmt.Fprintf(h, "FC=%q %q\n", b.fcExe(), fflags)
+			fmt.Fprintf(h, "FC=%q %q\n", b.fcExe(true), fflags)
 		}
 		// TODO(rsc): Should we include the SWIG version or Fortran/GCC/G++/Objective-C compiler versions?
 	}
@@ -2096,33 +2098,33 @@ var (
 // gccCmd returns a gcc command line prefix
 // defaultCC is defined in zdefaultcc.go, written by cmd/dist.
 func (b *Builder) GccCmd(incdir, workdir string) []string {
-	return b.compilerCmd(b.ccExe(), incdir, workdir)
+	return b.compilerCmd(b.ccExe(false), incdir, workdir)
 }
 
 // gxxCmd returns a g++ command line prefix
 // defaultCXX is defined in zdefaultcc.go, written by cmd/dist.
 func (b *Builder) GxxCmd(incdir, workdir string) []string {
-	return b.compilerCmd(b.cxxExe(), incdir, workdir)
+	return b.compilerCmd(b.cxxExe(false), incdir, workdir)
 }
 
 // gfortranCmd returns a gfortran command line prefix.
 func (b *Builder) gfortranCmd(incdir, workdir string) []string {
-	return b.compilerCmd(b.fcExe(), incdir, workdir)
+	return b.compilerCmd(b.fcExe(false), incdir, workdir)
 }
 
 // ccExe returns the CC compiler setting without all the extra flags we add implicitly.
-func (b *Builder) ccExe() []string {
-	return b.compilerExe(origCC, cfg.DefaultCC(cfg.Goos, cfg.Goarch))
+func (b *Builder) ccExe(filtered bool) []string {
+	return b.compilerExe(origCC, cfg.DefaultCC(cfg.Goos, cfg.Goarch), filtered)
 }
 
 // cxxExe returns the CXX compiler setting without all the extra flags we add implicitly.
-func (b *Builder) cxxExe() []string {
-	return b.compilerExe(origCXX, cfg.DefaultCXX(cfg.Goos, cfg.Goarch))
+func (b *Builder) cxxExe(filtered bool) []string {
+	return b.compilerExe(origCXX, cfg.DefaultCXX(cfg.Goos, cfg.Goarch), filtered)
 }
 
 // fcExe returns the FC compiler setting without all the extra flags we add implicitly.
-func (b *Builder) fcExe() []string {
-	return b.compilerExe(os.Getenv("FC"), "gfortran")
+func (b *Builder) fcExe(filtered bool) []string {
+	return b.compilerExe(os.Getenv("FC"), "gfortran", filtered)
 }
 
 // compilerExe returns the compiler to use given an
@@ -2131,11 +2133,14 @@ func (b *Builder) fcExe() []string {
 // of the compiler but can have additional arguments if they
 // were present in the environment value.
 // For example if CC="gcc -DGOPHER" then the result is ["gcc", "-DGOPHER"].
-func (b *Builder) compilerExe(envValue string, def string) []string {
+func (b *Builder) compilerExe(envValue string, def string, filtered bool) []string {
 	compiler := strings.Fields(envValue)
 	if len(compiler) == 0 {
 		compiler = []string{def}
 	}
+	if filtered {
+		return append(compiler[0:1], filterCompilerFlags(compiler[1:])...)
+	}
 	return compiler
 }
 
@@ -2285,8 +2290,23 @@ func envList(key, def string) []string {
 	return strings.Fields(v)
 }
 
+var filterFlags = os.Getenv("CGO_PEDANTIC") == ""
+
+func filterCompilerFlags(flags []string) []string {
+	var newflags []string
+	if !filterFlags {
+		return flags
+	}
+	for _, flag := range flags {
+		if strings.HasPrefix(flag, "-m") {
+			newflags = append(newflags, flag)
+		}
+	}
+	return newflags
+}
+
 // CFlags returns the flags to use when invoking the C, C++ or Fortran compilers, or cgo.
-func (b *Builder) CFlags(p *load.Package) (cppflags, cflags, cxxflags, fflags, ldflags []string, err error) {
+func (b *Builder) CFlags(p *load.Package, filtered bool) (cppflags, cflags, cxxflags, fflags, ldflags []string, err error) {
 	defaults := "-g -O2"
 
 	if cppflags, err = buildFlags("CPPFLAGS", "", p.CgoCPPFLAGS, checkCompilerFlags); err != nil {
@@ -2304,6 +2324,13 @@ func (b *Builder) CFlags(p *load.Package) (cppflags, cflags, cxxflags, fflags, l
 	if ldflags, err = buildFlags("LDFLAGS", defaults, p.CgoLDFLAGS, checkLinkerFlags); err != nil {
 		return
 	}
+	if filtered {
+		cppflags = filterCompilerFlags(cppflags)
+		cflags = filterCompilerFlags(cflags)
+		cxxflags = filterCompilerFlags(cxxflags)
+		fflags = filterCompilerFlags(fflags)
+		ldflags = filterCompilerFlags(ldflags)
+	}
 
 	return
 }
@@ -2319,7 +2346,7 @@ var cgoRe = regexp.MustCompile(`[/\\:]`)
 
 func (b *Builder) cgo(a *Action, cgoExe, objdir string, pcCFLAGS, pcLDFLAGS, cgofiles, gccfiles, gxxfiles, mfiles, ffiles []string) (outGo, outObj []string, err error) {
 	p := a.Package
-	cgoCPPFLAGS, cgoCFLAGS, cgoCXXFLAGS, cgoFFLAGS, cgoLDFLAGS, err := b.CFlags(p)
+	cgoCPPFLAGS, cgoCFLAGS, cgoCXXFLAGS, cgoFFLAGS, cgoLDFLAGS, err := b.CFlags(p, false)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -2679,7 +2706,7 @@ func (b *Builder) swigIntSize(objdir string) (intsize string, err error) {
 
 // Run SWIG on one SWIG input file.
 func (b *Builder) swigOne(a *Action, p *load.Package, file, objdir string, pcCFLAGS []string, cxx bool, intgosize string) (outGo, outC string, err error) {
-	cgoCPPFLAGS, cgoCFLAGS, cgoCXXFLAGS, _, _, err := b.CFlags(p)
+	cgoCPPFLAGS, cgoCFLAGS, cgoCXXFLAGS, _, _, err := b.CFlags(p, false)
 	if err != nil {
 		return "", "", err
 	}