debug/macho: Invalid index reference in macho file Dysyms.IndirectSyms

[gcmurphy]

I may be misunderstanding the expected usage of debug/macho but I'm encountering the following and it doesn't seem correct to me.

The godoc for the macho package has this definition:

 type Dysymtab struct {
        LoadBytes
        DysymtabCmd
        IndirectSyms []uint32 // indices into Symtab.Syms
}

So I would expect given the c program:

#include <stdio.h>
int main(void){
    puts("Hello World");
}

/*
$ gcc foo.c -o foo
$ gcc -v
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
Target: x86_64-apple-darwin14.1.0
Thread model: posix
*/

And reading the symbols using the following go code:

package main

import (
    "debug/macho"
    "fmt"
    "os"
)

func main(){

    for _, path := range os.Args[1:] {

        file, err := macho.Open(path)
        if err != nil {
            fmt.Printf("error: could not open macho file: %v - %v\n", path, err)
            os.Exit(1)
        }
        defer file.Close()

        fmt.Printf("Dysymtab for %v\n", path)
        for _, index := range file.Dysymtab.IndirectSyms {
            if index < uint32(len(file.Symtab.Syms)) {
                fmt.Println(file.Symtab.Syms[index].Name)
            } else {
                fmt.Printf("wtf? >>>>>> %v, max = %v\n", index, len(file.Symtab.Syms))
            }
        }

    }
}

To not see this in the output:

$ go run testcase.go a.out  | grep wtf
wtf? >>>>>> 1073741824, max = 4

This looks suspect to me. Although I may be using the library incorrectly.

[gcmurphy]

Sorry the version of go I'm using is -

$ go version
go version go1.4.1 darwin/amd64

[minux]

I don't think there is anything wrong. run "otool -Iv a.out" and note that there is an absolute symbol. $ otool -Iv a.out a.out: Indirect symbols for (__TEXT,__stubs) 1 entries address index name 0x0000000100000f44 2 _puts Indirect symbols for (__DATA,__nl_symbol_ptr) 2 entries address index name 0x0000000100001000 3 dyld_stub_binder 0x0000000100001008 ABSOLUTE Indirect symbols for (__DATA,__la_symbol_ptr) 1 entries address index name 0x0000000100001010 2 _puts $ go run issue10178.go a.out Dysymtab for a.out _puts dyld_stub_binder wtf? >>>>>> 1073741824, max = 4 _puts

[minux]

Just FYI, in /usr/include/mach-o/loader.h, we have

#define INDIRECT_SYMBOL_ABS     0x40000000

And sure enough 0x40000000 == 1073741824.

[gcmurphy]

Thanks.