cmd/compile: fails to run on some ARMv7 processors

[aka-mj]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
go version go1.6 linux/amd64

2. What operating system and processor architecture are you using (go env)?
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/mjohn/workspace/gopath"
GORACE=""
GOROOT="/home/mjohn/software/go"
GOTOOLDIR="/home/mjohn/software/go/pkg/tool/linux_amd64"
GO15VENDOREXPERIMENT="1"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
CXX="g++"
CGO_ENABLED="1"

3. What did you do?
(Use play.golang.org to provide a runnable example, if possible.)
I am cross-compiling for ARMv7. I have a simple hello world program.

package main

import "fmt"

func main() {
    fmt.Println("Hello, tester")
}

I built Go to cross-compile.
GOARCH=arm GOARM=7 GOOS=linux ./make.bash

Then compiled the code.
GOARCH=arm GOARM=7 GOOS=linux go build hello.go

The resulting executable runs on one ARMv7 board but fails on another with a different ARMv7 processor.

Processor where code runs:
Freescale i.MX53

$ cat /proc/cpuinfo
Processor       : ARMv7 Processor rev 5 (v7l)
BogoMIPS        : 799.53
Features        : swp half thumb fastmult vfp edsp neon vfpv3
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x2
CPU part        : 0xc08
CPU revision    : 5

Processor where code does not run:
Ti am3352

$ cat /proc/cpuinfo
Processor       : ARMv7 Processor rev 2 (v7l)
BogoMIPS        : 797.80
Features        : swp half thumb fastmult vfp edsp thumbee neon vfpv3 tls
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x3
CPU part        : 0xc08
CPU revision    : 2

4. What did you expect to see?
./hello
Hello, tester

5. What did you see instead?
./hello
Illegal instruction

[ianlancetaylor]

Can you find out what the illegal instruction is? It should work to run something like

gdb ./hello
r
x/i $pc

[aka-mj]

Sure, see below:

(gdb) r
Starting program: /root/hello
Cannot access memory at address 0x0
Cannot access memory at address 0x0

Program received signal SIGILL, Illegal instruction.
0x00067620 in ?? ()
(gdb) x/i $pc
=> 0x67620:     mcr2    4, 7, r8, cr2, cr0, {7}

[mwhudson]

My understand and experiments both suggest that we don't generate the mcr2 instruction. (I tried this:

(master)mwhudson@aeglos:go$ GOARCH=arm GOARM=7 GOOS=linux go build /opt/opensource/go-test-cases/hello.go 
(master)mwhudson@aeglos:go$ objdump -d trivial | grep -i mcr

so maybe somehow that's executing data that is not intended to be code?

[davecheney]

I know it's not directly helpful to the problem at hand, but

I built Go to cross-compile.
GOARCH=arm GOARM=7 GOOS=linux ./make.bash

This is not necessary since Go 1.5, and in fact could be considered to be the wrong thing to do. To cross compile all that is necessary is GOOS=NNN GOARCH=YYY go build $PKG

[minux]

Could you please make the original hello executable available somewhere? I'd like to take a look. Thanks.

[aka-mj]

@minux Sure, you can get it here

[minux]

It seems the binary is completely corrupted.

Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] go.buildid NULL 00000000 000000 000000 00 0 0 0
[ 1] o.buildid PROGBITS 00011000 001000 0abf84 00 AX 0 0 4
[ 2] b PROGBITS 000bd000 0ad000 04bc90 00 A 0 0 8
[ 3] b PROGBITS 00108c90 0f8c90 001028 00 A 0 0 4
[ 4] bbrev PROGBITS 00109cb8 0f9cb8 000000 00 A 0 0 1
[ 5] ug_aranges PROGBITS 00109cb8 0f9cb8 03e40e 00 A 0 0 8
[ 6] STRTAB 00000000 1380c8 00012a 00 0 0 1
[ 7] did PROGBITS 00149000 139000 001740 00 WA 0 0 8
[ 8] a PROGBITS 0014a740 13a740 001230 00 WA 0 0 8
[ 9] ata NOBITS 0014b970 13b970 00d62c 00 WA 0 0 8
[10] typelink NOBITS 00158fa0 148fa0 004720 00 WA 0 0 8
[11] gosymtab NOTE 00010fc8 000fc8 000038 00 A 0 0 4
[12] .debug_frame SYMTAB 00000000 13c000 00a630 10 13 136 4
[13] rame STRTAB 00000000 146630 00ead0 00 0 0 1
[14] bug_info PROGBITS 00000000 155100 0000ff 00 0 0 1
[15] pubnames PROGBITS 00000000 1551ff 0108e8 00 0 0 1
[16] oc PROGBITS 00000000 165ae7 00de84 00 0 0 1
[17] info PROGBITS 00000000 17396b 03a022 00 0 0 1
[18] PROGBITS 00000000 1ad98d 01144a 00 0 0 1
[19] ug_gdb_scripts PROGBITS 00000000 1bedd7 0064cc 00 0 0 1
[20] g_line PROGBITS 00000000 1c52a3 000020 00 0 0 1
[21] PROGBITS 00000000 1c52c3 000034 00 0 0 1

Symbol table '.debug_frame' contains 2659 entries:
Num: Value Size Type Bind Vis Ndx Name
0: b8000000 4252 NOTYPE LOCAL DEFAULT 256
1: 3c000000 4194 NOTYPE LOCAL DEFAULT 256
2: 34000000 4114 NOTYPE LOCAL DEFAULT 256
3: 48000000 3637 NOTYPE LOCAL DEFAULT 256
4: 2c000000 4203 NOTYPE LOCAL DEFAULT 256
5: 60000000 0xcc001068 FUNC LOCAL DEFAULT 256

6760c: dae04bb0 ble ff87a4d4 <(null)+0x387a405>
67610: 00eaffff strdeq pc, [sl], #255 ; 0xff ;

67614: 04e59d00 strbteq r9, [r5], #3328 ; 0xd00
67618: 04e28d10 strbteq r8, [r2], #3344 ; 0xd10
6761c: 00e59f40 rsceq r9, r5, r0, asr #30
67620: fee284f0 mcr2 4, 7, r8, cr2, cr0, {7}
67624: 2ceaffff stclcs 15, cr15, [sl], #1020 ; 0x3fc
67628: 03000676 movweq r0, #1654 ; 0x676

[aka-mj]

I removed Go from my system, and preformed a fresh install. This time I took @davecheney advice and did not define GOARCH or GOARM on the install, only while building the executable.

$ ./make.bash
....
$ GOARCH=arm GOARM=7 go build hello.go

This produces the expected result on the target when ran.