cmd/compile: add -dolinkobj flag

When set to false, the -dolinkobj flag instructs the compiler
not to generate or emit linker information.

This is handy when you need the compiler's export data,
e.g. for use with go/importer,
but you want to avoid the cost of full compilation.

This must be used with care, since the resulting
files are unusable for linking.

This CL interacts with #18369,
where adding gcflags and ldflags to buildid has been mooted.
On the one hand, adding gcflags would make safe use of this
flag easier, since if the full object files were needed,
a simple 'go install' would fix it.
On the other hand, this would mean that
'go install -gcflags=-dolinkobj=false' would rebuild the object files,
although any existing object files would probably suffice.

Change-Id: I8dc75ab5a40095c785c1a4d2260aeb63c4d10f73
Reviewed-on: https://go-review.googlesource.com/37384
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index 9e5d1843d0fd68bd8c16398cd104745a499474ff..95c1124f9e0bc4d13e70e51a7fc4439485dec0f6 100644 (file)
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -118,6 +118,7 @@ var pragcgobuf string
 
 var outfile string
 var linkobj string
+var dolinkobj bool
 
 var bout *bio.Writer
 

diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
index d1dbe45c71acbc3bc8a6a305052848e5f5927ff8..2b1ae860d69cf343382ce32e2bd0f2cd825292a1 100644 (file)
--- a/src/cmd/compile/internal/gc/main.go
+++ b/src/cmd/compile/internal/gc/main.go
@@ -181,6 +181,7 @@ func Main() {
        obj.Flagcount("live", "debug liveness analysis", &debuglive)
        obj.Flagcount("m", "print optimization decisions", &Debug['m'])
        flag.BoolVar(&flag_msan, "msan", false, "build code compatible with C/C++ memory sanitizer")
+       flag.BoolVar(&dolinkobj, "dolinkobj", true, "generate linker-specific objects; if false, some invalid code may compile")
        flag.BoolVar(&nolocalimports, "nolocalimports", false, "reject local (relative) imports")
        flag.StringVar(&outfile, "o", "", "write output to `file`")
        flag.StringVar(&myimportpath, "p", "", "set expected package import `path`")
@@ -450,38 +451,40 @@ func Main() {
        timings.Start("fe", "escapes")
        escapes(xtop)
 
-       // Phase 7: Transform closure bodies to properly reference captured variables.
-       // This needs to happen before walk, because closures must be transformed
-       // before walk reaches a call of a closure.
-       timings.Start("fe", "xclosures")
-       for _, n := range xtop {
-               if n.Op == ODCLFUNC && n.Func.Closure != nil {
-                       Curfn = n
-                       transformclosure(n)
+       if dolinkobj {
+               // Phase 7: Transform closure bodies to properly reference captured variables.
+               // This needs to happen before walk, because closures must be transformed
+               // before walk reaches a call of a closure.
+               timings.Start("fe", "xclosures")
+               for _, n := range xtop {
+                       if n.Op == ODCLFUNC && n.Func.Closure != nil {
+                               Curfn = n
+                               transformclosure(n)
+                       }
                }
-       }
 
-       Curfn = nil
+               Curfn = nil
 
-       // Phase 8: Compile top level functions.
-       // Don't use range--walk can add functions to xtop.
-       timings.Start("be", "compilefuncs")
-       fcount = 0
-       for i := 0; i < len(xtop); i++ {
-               n := xtop[i]
-               if n.Op == ODCLFUNC {
-                       funccompile(n)
-                       fcount++
+               // Phase 8: Compile top level functions.
+               // Don't use range--walk can add functions to xtop.
+               timings.Start("be", "compilefuncs")
+               fcount = 0
+               for i := 0; i < len(xtop); i++ {
+                       n := xtop[i]
+                       if n.Op == ODCLFUNC {
+                               funccompile(n)
+                               fcount++
+                       }
                }
-       }
-       timings.AddEvent(fcount, "funcs")
+               timings.AddEvent(fcount, "funcs")
 
-       if nsavederrors+nerrors == 0 {
-               fninit(xtop)
-       }
+               if nsavederrors+nerrors == 0 {
+                       fninit(xtop)
+               }
 
-       if compiling_runtime {
-               checknowritebarrierrec()
+               if compiling_runtime {
+                       checknowritebarrierrec()
+               }
        }
 
        // Phase 9: Check external declarations.

diff --git a/src/cmd/compile/internal/gc/obj.go b/src/cmd/compile/internal/gc/obj.go
index 6d5f2aa208d229d92dd41f0f4e75432330653c90..bec5d89d758e7119e363bc286840e78319f37129 100644 (file)
--- a/src/cmd/compile/internal/gc/obj.go
+++ b/src/cmd/compile/internal/gc/obj.go
@@ -41,12 +41,16 @@ const (
 )
 
 func dumpobj() {
+       if !dolinkobj {
+               dumpobj1(outfile, modeCompilerObj)
+               return
+       }
        if linkobj == "" {
                dumpobj1(outfile, modeCompilerObj|modeLinkerObj)
-       } else {
-               dumpobj1(outfile, modeCompilerObj)
-               dumpobj1(linkobj, modeLinkerObj)
+               return
        }
+       dumpobj1(outfile, modeCompilerObj)
+       dumpobj1(linkobj, modeLinkerObj)
 }
 
 func dumpobj1(outfile string, mode int) {