cmd/go, runtime/cgo: rewrite darwin/arm panicmem setup to avoid init function

Init functions are problematic because we want cmd/link to be
able to insert an import of runtime/cgo for external linking.
For all the other systems that just means putting runtime/cgo into
the binary. The linker is not set up to generate calls to init functions,
and luckily this one can be avoided entirely.

This means people don't have to import _ "runtime/cgo" in their
iOS programs anymore. The linker's default import is now enough.

This CL also adjusts cmd/go to record the linker's default import,
now that the explicit import is gone.

Change-Id: I81d23476663e03664f90d531c24db2e4f2e6c66b
Reviewed-on: https://go-review.googlesource.com/68490
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/cmd/go/internal/cfg/cfg.go b/src/cmd/go/internal/cfg/cfg.go
index b50074f0af38da63949eaf1577c5761f315bd976..0d8e264eb754cbd046c68ad89d46accc0a5b4f02 100644 (file)
--- a/src/cmd/go/internal/cfg/cfg.go
+++ b/src/cmd/go/internal/cfg/cfg.go
@@ -131,7 +131,24 @@ func isGOROOT(path string) bool {
 
 // ExternalLinkingForced reports whether external linking is being
 // forced even for programs that do not use cgo.
-func ExternalLinkingForced() bool {
+func ExternalLinkingForced(inGoroot bool) bool {
+       // Some targets must use external linking even inside GOROOT.
+       switch BuildContext.GOOS {
+       case "android":
+               return true
+       case "darwin":
+               switch BuildContext.GOARCH {
+               case "arm", "arm64":
+                       return true
+               }
+       }
+
+       // Otherwise we disable forcing of external linking for GOROOT binaries.
+       // This is primarily for cgo, so we will be able to relax this soon.
+       if inGoroot {
+               return false
+       }
+
        if !BuildContext.CgoEnabled {
                return false
        }
@@ -151,5 +168,6 @@ func ExternalLinkingForced() bool {
                        linkmodeExternal = true
                }
        }
+
        return BuildBuildmode == "c-shared" || BuildBuildmode == "plugin" || pieCgo || BuildLinkshared || linkmodeExternal
 }

diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index 63e58c6247b72355404a3b30a74e76dd0c7bec9e..dace766aed894e66f2cd3bb2e0f146864ca6f514 100644 (file)
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -946,7 +946,7 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
                importPaths = append(importPaths, "syscall")
        }
 
-       if p.Name == "main" && !p.Goroot && cfg.ExternalLinkingForced() {
+       if p.Name == "main" && cfg.ExternalLinkingForced(p.Goroot) {
                importPaths = append(importPaths, "runtime/cgo")
        }
 

diff --git a/src/cmd/go/internal/test/test.go b/src/cmd/go/internal/test/test.go
index bdedd256511a7f775fd337363e6599f86e340e33..c3810feb0d1b19586511ae66524e51eee5a1774e 100644 (file)
--- a/src/cmd/go/internal/test/test.go
+++ b/src/cmd/go/internal/test/test.go
@@ -815,16 +815,10 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
                },
        }
 
-       // The generated main also imports testing, regexp, os, and maybe runtime/cgo.
+       // The generated main also imports testing, regexp, and os.
        stk.Push("testmain")
-       forceCgo := false
-       if cfg.BuildContext.GOOS == "darwin" {
-               if cfg.BuildContext.GOARCH == "arm" || cfg.BuildContext.GOARCH == "arm64" {
-                       forceCgo = true
-               }
-       }
        deps := testMainDeps
-       if cfg.ExternalLinkingForced() || forceCgo {
+       if cfg.ExternalLinkingForced(pmain.Goroot) {
                deps = str.StringList(deps, "runtime/cgo")
        }
        for _, dep := range deps {
@@ -889,8 +883,6 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
                recompileForTest(pmain, p, ptest)
        }
 
-       t.NeedCgo = forceCgo
-
        for _, cp := range pmain.Internal.Imports {
                if len(cp.Internal.CoverVars) > 0 {
                        t.Cover = append(t.Cover, coverInfo{cp, cp.Internal.CoverVars})
@@ -1319,7 +1311,6 @@ type testFuncs struct {
        NeedTest    bool
        ImportXtest bool
        NeedXtest   bool
-       NeedCgo     bool
        Cover       []coverInfo
 }
 
@@ -1448,10 +1439,6 @@ import (
 {{range $i, $p := .Cover}}
        _cover{{$i}} {{$p.Package.ImportPath | printf "%q"}}
 {{end}}
-
-{{if .NeedCgo}}
-       _ "runtime/cgo"
-{{end}}
 )
 
 var tests = []testing.InternalTest{

diff --git a/src/runtime/cgo/gcc_signal2_darwin_armx.c b/src/runtime/cgo/gcc_signal2_darwin_armx.c
new file mode 100644 (file)
index 0000000..6da623b
--- /dev/null
+++ b/src/runtime/cgo/gcc_signal2_darwin_armx.c
@@ -0,0 +1,13 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build lldb
+// +build darwin
+// +build arm arm64
+
+// Used by gcc_signal_darwin_armx.c when doing the test build during cgo.
+// We hope that for real binaries the definition provided by Go will take precedence
+// and the linker will drop this .o file altogether, which is why this definition
+// is all by itself in its own file.
+void xx_cgo_panicmem(void) {}

diff --git a/src/runtime/cgo/gcc_signal_darwin_armx.c b/src/runtime/cgo/gcc_signal_darwin_armx.c
index a2d520bce8f9d57677bf3dcfeaa85bd588c0da0d..3ab1d8b0d6f75f7a8dc0620aa3f6fefb30ad0e15 100644 (file)
--- a/src/runtime/cgo/gcc_signal_darwin_armx.c
+++ b/src/runtime/cgo/gcc_signal_darwin_armx.c
@@ -39,7 +39,8 @@
 #include "libcgo.h"
 #include "libcgo_unix.h"
 
-uintptr_t x_cgo_panicmem;
+void xx_cgo_panicmem(void);
+uintptr_t x_cgo_panicmem = (uintptr_t)xx_cgo_panicmem;
 
 static pthread_mutex_t mach_exception_handler_port_set_mu;
 static mach_port_t mach_exception_handler_port_set = MACH_PORT_NULL;

diff --git a/src/runtime/cgo/gcc_signal_darwin_lldb.c b/src/runtime/cgo/gcc_signal_darwin_lldb.c
index 12cc388400fe3bfb1f5b5eb4442f07dd31dc7170..54d91f6390975b8ea7020d8b6c495234f13b01c9 100644 (file)
--- a/src/runtime/cgo/gcc_signal_darwin_lldb.c
+++ b/src/runtime/cgo/gcc_signal_darwin_lldb.c
@@ -8,7 +8,5 @@
 
 #include <stdint.h>
 
-uintptr_t x_cgo_panicmem;
-
 void darwin_arm_init_thread_exception_port() {}
 void darwin_arm_init_mach_exception_handler() {}

diff --git a/src/runtime/cgo/signal_darwin_armx.go b/src/runtime/cgo/signal_darwin_armx.go
index 9f6741eb08581976b4ebfb0315476c8a6223340a..e1d9e54c462f1b46cd8cd08f76034cbbd4238a61 100644 (file)
--- a/src/runtime/cgo/signal_darwin_armx.go
+++ b/src/runtime/cgo/signal_darwin_armx.go
@@ -7,29 +7,7 @@
 
 package cgo
 
-import "unsafe"
-
-//go:cgo_import_static x_cgo_panicmem
-//go:linkname x_cgo_panicmem x_cgo_panicmem
-var x_cgo_panicmem uintptr
-
-// use a pointer to avoid relocation of external symbol in __TEXT
-// make linker happy
-var _cgo_panicmem = &x_cgo_panicmem
-
-// TODO(crawshaw): move this into x_cgo_init, it will not run until
-// runtime has finished loading, which may be after its use.
-func init() {
-       *_cgo_panicmem = funcPC(panicmem)
-}
-
-func funcPC(f interface{}) uintptr {
-       var ptrSize = unsafe.Sizeof(uintptr(0))
-       return **(**uintptr)(add(unsafe.Pointer(&f), ptrSize))
-}
-
-func add(p unsafe.Pointer, x uintptr) unsafe.Pointer {
-       return unsafe.Pointer(uintptr(p) + x)
-}
+import _ "unsafe"
 
+//go:cgo_export_static panicmem xx_cgo_panicmem
 func panicmem()