cmd/go: dylib built as buildmode=c-shared causes 'overlapping segments' after codesign by Xcode on OS X

[albertjin]

Go 1.5.1 on OS X 10.10.5 with Xcode 7

1. Save test code as dy.go

   package main
   
   import "C"
   
   import (
      "fmt"
   )
   
   //export PrintHello
   func PrintHello() {
       fmt.Println("hello")
   }
   
   func main() {
   }

2. Build

   go build -v -o dy.dylib -buildmode=c-shared dy.go
   

3. Use it in an Xcode app project

   Add dy.dylib to an Xcode app project for linking and setup the project in TARGETS > [targetname] > Build Phases
   
   Notice that the option Code Sign on Copy is selected, otherwise the whole bundle cannot pass code sign. In the screenshot, the text for Run Script is

   install_name_tool -change dy.dylib @loader_path/../Frameworks/dy.dylib "$TARGET_BUILD_DIR/$TARGET_NAME.app/Contents/MacOS/$PRODUCT_NAME"
   

4. Build the Xcode project successfully and run it
   Here is the error,

   dyld: Library not loaded: @loader_path/../Frameworks/dy.dylib
    Referenced from: /Users/albert/Library/Developer/Xcode/DerivedData/qr-cavcmuynmurgdxafrfnfvdoaxezo/Build/Products/Debug/qr.app/Contents/MacOS/qr
   Reason: no suitable image found.  Did find:
   /Users/albert/Library/Developer/Xcode/DerivedData/qr-cavcmuynmurgdxafrfnfvdoaxezo/Build/Products/Debug/qr.app/Contents/MacOS/../Frameworks/dy.dylib: overlapping segments
   /Users/albert/Library/Developer/Xcode/DerivedData/qr-cavcmuynmurgdxafrfnfvdoaxezo/Build/Products/Debug/qr.app/Contents/MacOS/../Frameworks/dy.dylib: overlapping segments
   

[rakyll]

/cc @crawshaw

[rsc]

Does anyone know any more about what is going wrong here?

[glycerine]

just a guess, the -o dy.dylib looks suspicious, as I expect a .so as output.

http://stackoverflow.com/questions/2339679/what-are-the-differences-between-so-and-dylib-on-osx

"The Mach-O object file format used by Mac OS X for executables and libraries distinguishes between shared libraries and dynamically loaded modules. Use otool -hv some_file to see the filetype of some_file."

[Qix-]

Sooooo this is a huge 👎 on Go's part. How do you create a .dylib? This seems like a glaring feature hole.

[glycerine]

@qix, the shared library build modes are a "still being implemented" feature (especially on OSX) -- only some of the new buildmodes that Ian defined in the spec are implemented, and support across platforms is still quite limited.

You can help by playing with the feature and reporting rough edges in your specific cases.

[Qix-]

@glycerine such as on linux, writing to a .so produces an ar archive?... Haha

[sctb]

Is this still an issue? Using go 1.6.1 under 10.11.4, I'm able to produce a dylib, codesign it, then use install_name_tool to change one of the referenced libraries:

$ go build -v -o dy.dylib -buildmode=c-shared dy.go

$ codesign --display dy.dylib 
dy.dylib: code object is not signed at all

$ codesign -s - dy.dylib 

$ codesign --display --verbose=4 dy.dylib 
Executable=/Users/sctb/Documents/go/src/scratch/dy.dylib
Identifier=dy-555549440baae12e4a2736199fdd79b6c9919bc0
Format=Mach-O thin (x86_64)
CodeDirectory v=20100 size=17564 flags=0x2(adhoc) hashes=542+4 location=embedded
Hash type=sha256 size=32
CandidateCDHash sha1=6dcc99af796f36291ca08bf4d6696db6a1c6fc1a
CandidateCDHash sha256=72f971707b73f738838dd586fb2bf905581723b2
Hash choices=sha1,sha256
CDHash=72f971707b73f738838dd586fb2bf905581723b2
Signature=adhoc
Info.plist=not bound
TeamIdentifier=not set
Sealed Resources=none
Internal requirements count=0 size=12

$ file dy.dylib 
dy.dylib: Mach-O 64-bit dynamically linked shared library x86_64

$ otool -L dy.dylib 
dy.dylib:
    dy.dylib (compatibility version 0.0.0, current version 0.0.0)
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)

$ install_name_tool -change /usr/lib/libSystem.B.dylib /bar/system.dylib dy.dylib

$ otool -L dy.dylib
dy.dylib:
    dy.dylib (compatibility version 0.0.0, current version 0.0.0)
    /bar/system.dylib (compatibility version 1.0.0, current version 1226.10.1)

[lunixbochs]

This doesn't seem to work under Go 1.8 on OS X 10.12 Sierra.