[Qemu-devel] [Bug 1839325] [NEW] Go programs crash on qemu-sh4 due to issues with atomics

[Qemu-devel] [Bug 1839325] [NEW] Go programs crash on qemu-sh4 due to issues with atomics

[John Paul Adrian Glaubitz]

Public bug reported:

After #1738545 [1] was fixed, Go applications work fine on qemu-arm but
still crash on qemu-sh4. From the backtrace, it looks like an issue with
the atomics in qemu-sh4:

(sid-sh4-sbuild)root@epyc:/# cat hello.go
package main

import "fmt"

func main() {
      fmt.Println("hello world")
}

(sid-sh4-sbuild)root@epyc:/# gccgo-9 hello.go -o hello
(sid-sh4-sbuild)root@epyc:/# ./hello 
panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
fatal error: panic on system stack
panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
fatal error: panic on system stack

runtime stack:
runtime..z2finternal..z2fatomic.Load64
        ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
runtime_mstart
        ../../../src/libgo/runtime/proc.c:596

goroutine 1 [running]:
        goroutine running on other thread; stack unavailable

runtime stack:
runtime..z2finternal..z2fatomic.Load64
        ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
runtime_mstart
        ../../../src/libgo/runtime/proc.c:596
(sid-sh4-sbuild)root@epyc:/#

The same sample Go program runs fine on my SH7785LCR SH4 evaluation
board:

root@tirpitz:~> uname -a
Linux tirpitz 3.16.7-ckt7 #8 PREEMPT Fri Oct 21 18:47:41 CEST 2016 sh4a GNU/Linux
root@tirpitz:~> cat hello.go
package main

import "fmt"

func main() {
      fmt.Println("hello world")
}

root@tirpitz:~> gccgo-9 hello.go -o hello
root@tirpitz:~> ./hello 
hello world
root@tirpitz:~>

Please note: In order to be able to reproduce this, one also needs to
revert commit 61dedf2af7 [2], otherwise the Go application crashes
differently:

(sid-sh4-sbuild)root@epyc:/# ./hello        
Unhandled trap: 0x180
pc=0x7e5f7f9e sr=0x00000000 pr=0x7ee3d582 fpscr=0x00080004
spc=0x00000000 ssr=0x00000000 gbr=0x7e590480 vbr=0x00000000
sgr=0x00000000 dbr=0x00000000 delayed_pc=0x7e5f7f60 fpul=0x00034f3b
r0=0x008007d4 r1=0x00000000 r2=0xfffe0b2a r3=0x00000002
r4=0x008006e4 r5=0x00872000 r6=0x00200000 r7=0x00000000
r8=0x7f7bca7c r9=0x7fffebd4 r10=0x00800480 r11=0x7f7bc0f0
r12=0x7f7a3fa4 r13=0x008004c0 r14=0x7f7b2238 r15=0x7fffebd0
r16=0x00000000 r17=0x00000000 r18=0x00000000 r19=0x00000000
r20=0x00000000 r21=0x00000000 r22=0x00000000 r23=0x00000000
(sid-sh4-sbuild)root@epyc:/#

> [1] https://bugs.launchpad.net/bugs/1738545
> [2] https://bugs.launchpad.net/bugs/1796520

** Affects: qemu
     Importance: Undecided
         Status: New

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1839325

Title:
  Go programs crash on qemu-sh4 due to issues with atomics

Status in QEMU:
  New

Bug description:
  After #1738545 [1] was fixed, Go applications work fine on qemu-arm
  but still crash on qemu-sh4. From the backtrace, it looks like an
  issue with the atomics in qemu-sh4:

  (sid-sh4-sbuild)root@epyc:/# cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  (sid-sh4-sbuild)root@epyc:/# gccgo-9 hello.go -o hello
  (sid-sh4-sbuild)root@epyc:/# ./hello 
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596

  goroutine 1 [running]:
          goroutine running on other thread; stack unavailable

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596
  (sid-sh4-sbuild)root@epyc:/#

  The same sample Go program runs fine on my SH7785LCR SH4 evaluation
  board:

  root@tirpitz:~> uname -a
  Linux tirpitz 3.16.7-ckt7 #8 PREEMPT Fri Oct 21 18:47:41 CEST 2016 sh4a GNU/Linux
  root@tirpitz:~> cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  root@tirpitz:~> gccgo-9 hello.go -o hello
  root@tirpitz:~> ./hello 
  hello world
  root@tirpitz:~>

  Please note: In order to be able to reproduce this, one also needs to
  revert commit 61dedf2af7 [2], otherwise the Go application crashes
  differently:

  (sid-sh4-sbuild)root@epyc:/# ./hello        
  Unhandled trap: 0x180
  pc=0x7e5f7f9e sr=0x00000000 pr=0x7ee3d582 fpscr=0x00080004
  spc=0x00000000 ssr=0x00000000 gbr=0x7e590480 vbr=0x00000000
  sgr=0x00000000 dbr=0x00000000 delayed_pc=0x7e5f7f60 fpul=0x00034f3b
  r0=0x008007d4 r1=0x00000000 r2=0xfffe0b2a r3=0x00000002
  r4=0x008006e4 r5=0x00872000 r6=0x00200000 r7=0x00000000
  r8=0x7f7bca7c r9=0x7fffebd4 r10=0x00800480 r11=0x7f7bc0f0
  r12=0x7f7a3fa4 r13=0x008004c0 r14=0x7f7b2238 r15=0x7fffebd0
  r16=0x00000000 r17=0x00000000 r18=0x00000000 r19=0x00000000
  r20=0x00000000 r21=0x00000000 r22=0x00000000 r23=0x00000000
  (sid-sh4-sbuild)root@epyc:/#

  > [1] https://bugs.launchpad.net/bugs/1738545
  > [2] https://bugs.launchpad.net/bugs/1796520

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1839325/+subscriptions

[Qemu-devel] [Bug 1839325] Re: Go programs crash on qemu-sh4 due to issues with atomics

[Peter Maydell]

The immediate cause of the crash here is that the runtime invokes the
Load64() function on a pointer that isn't 8-aligned, which triggers a
hand-coded check-and-panic in the libgo code. I haven't yet tracked down
where that pointer came from.

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1839325

Title:
  Go programs crash on qemu-sh4 due to issues with atomics

Status in QEMU:
  New

Bug description:
  After #1738545 [1] was fixed, Go applications work fine on qemu-arm
  but still crash on qemu-sh4. From the backtrace, it looks like an
  issue with the atomics in qemu-sh4:

  (sid-sh4-sbuild)root@epyc:/# cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  (sid-sh4-sbuild)root@epyc:/# gccgo-9 hello.go -o hello
  (sid-sh4-sbuild)root@epyc:/# ./hello 
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596

  goroutine 1 [running]:
          goroutine running on other thread; stack unavailable

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596
  (sid-sh4-sbuild)root@epyc:/#

  The same sample Go program runs fine on my SH7785LCR SH4 evaluation
  board:

  root@tirpitz:~> uname -a
  Linux tirpitz 3.16.7-ckt7 #8 PREEMPT Fri Oct 21 18:47:41 CEST 2016 sh4a GNU/Linux
  root@tirpitz:~> cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  root@tirpitz:~> gccgo-9 hello.go -o hello
  root@tirpitz:~> ./hello 
  hello world
  root@tirpitz:~>

  Please note: In order to be able to reproduce this, one also needs to
  revert commit 61dedf2af7 [2], otherwise the Go application crashes
  differently:

  (sid-sh4-sbuild)root@epyc:/# ./hello        
  Unhandled trap: 0x180
  pc=0x7e5f7f9e sr=0x00000000 pr=0x7ee3d582 fpscr=0x00080004
  spc=0x00000000 ssr=0x00000000 gbr=0x7e590480 vbr=0x00000000
  sgr=0x00000000 dbr=0x00000000 delayed_pc=0x7e5f7f60 fpul=0x00034f3b
  r0=0x008007d4 r1=0x00000000 r2=0xfffe0b2a r3=0x00000002
  r4=0x008006e4 r5=0x00872000 r6=0x00200000 r7=0x00000000
  r8=0x7f7bca7c r9=0x7fffebd4 r10=0x00800480 r11=0x7f7bc0f0
  r12=0x7f7a3fa4 r13=0x008004c0 r14=0x7f7b2238 r15=0x7fffebd0
  r16=0x00000000 r17=0x00000000 r18=0x00000000 r19=0x00000000
  r20=0x00000000 r21=0x00000000 r22=0x00000000 r23=0x00000000
  (sid-sh4-sbuild)root@epyc:/#

  > [1] https://bugs.launchpad.net/bugs/1738545
  > [2] https://bugs.launchpad.net/bugs/1796520

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1839325/+subscriptions

[Qemu-devel] [Bug 1839325] Re: Go programs crash on qemu-sh4 due to issues with atomics

[Peter Maydell]

The non-8-aligned pointer is the runtime.work.empty field. The
compilation that I have of this binary has put the 'runtime.work' struct
at 0x6bfadc, which is only 4-aligned, and this won't work as the lfstack
fields it starts with are supposed to be 8-aligned. So it looks to me
like the compiler has miscompiled the binary somehow, and QEMU's actual
execution of it is OK.

I don't know if this is a general bug in the sh4 gccgo support (in which
case we must be succeeding on the real hardware by accident, probably by
finishing fast enough that the gc never kicks in), or if QEMU is mis-
executing the compiler somehow and a build done on the real hardware
puts the work struct at an 8-aligned address.

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1839325

Title:
  Go programs crash on qemu-sh4 due to issues with atomics

Status in QEMU:
  New

Bug description:
  After #1738545 [1] was fixed, Go applications work fine on qemu-arm
  but still crash on qemu-sh4. From the backtrace, it looks like an
  issue with the atomics in qemu-sh4:

  (sid-sh4-sbuild)root@epyc:/# cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  (sid-sh4-sbuild)root@epyc:/# gccgo-9 hello.go -o hello
  (sid-sh4-sbuild)root@epyc:/# ./hello 
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596

  goroutine 1 [running]:
          goroutine running on other thread; stack unavailable

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596
  (sid-sh4-sbuild)root@epyc:/#

  The same sample Go program runs fine on my SH7785LCR SH4 evaluation
  board:

  root@tirpitz:~> uname -a
  Linux tirpitz 3.16.7-ckt7 #8 PREEMPT Fri Oct 21 18:47:41 CEST 2016 sh4a GNU/Linux
  root@tirpitz:~> cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  root@tirpitz:~> gccgo-9 hello.go -o hello
  root@tirpitz:~> ./hello 
  hello world
  root@tirpitz:~>

  Please note: In order to be able to reproduce this, one also needs to
  revert commit 61dedf2af7 [2], otherwise the Go application crashes
  differently:

  (sid-sh4-sbuild)root@epyc:/# ./hello        
  Unhandled trap: 0x180
  pc=0x7e5f7f9e sr=0x00000000 pr=0x7ee3d582 fpscr=0x00080004
  spc=0x00000000 ssr=0x00000000 gbr=0x7e590480 vbr=0x00000000
  sgr=0x00000000 dbr=0x00000000 delayed_pc=0x7e5f7f60 fpul=0x00034f3b
  r0=0x008007d4 r1=0x00000000 r2=0xfffe0b2a r3=0x00000002
  r4=0x008006e4 r5=0x00872000 r6=0x00200000 r7=0x00000000
  r8=0x7f7bca7c r9=0x7fffebd4 r10=0x00800480 r11=0x7f7bc0f0
  r12=0x7f7a3fa4 r13=0x008004c0 r14=0x7f7b2238 r15=0x7fffebd0
  r16=0x00000000 r17=0x00000000 r18=0x00000000 r19=0x00000000
  r20=0x00000000 r21=0x00000000 r22=0x00000000 r23=0x00000000
  (sid-sh4-sbuild)root@epyc:/#

  > [1] https://bugs.launchpad.net/bugs/1738545
  > [2] https://bugs.launchpad.net/bugs/1796520

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1839325/+subscriptions

[Qemu-devel] [Bug 1839325] Re: Go programs crash on qemu-sh4 due to issues with atomics

[Peter Maydell]

I just did an objdump -x of the /usr/lib/sh4-linux-gnu/libgo.so.14,
which will be the shipped version from the Debian package, and in the
section header it has:

 24 .bss          000191f8  00fe74ec  00fe74ec  00fd74ec  2**2
                  ALLOC

and in the symbol table it has:

00ff98f4 l     O .bss   00000104              runtime.work

So the compiler has put the 'runtime.work' struct at a non-multiple-of-8
offset into the bss, and it's given the BSS alignment requirements that
are only 4-aligned, not 8-aligned. That means it's random luck whether
the struct gets 8-aligned or not.

This looks to me like it's a bug in the sh4 gccgo --
https://go101.org/article/memory-layout.html says that the first word in
a struct or variable is supposed to be guaranteed to be 8-aligned, so
the compiler needs to align things more strictly than it is currently
doing.

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1839325

Title:
  Go programs crash on qemu-sh4 due to issues with atomics

Status in QEMU:
  New

Bug description:
  After #1738545 [1] was fixed, Go applications work fine on qemu-arm
  but still crash on qemu-sh4. From the backtrace, it looks like an
  issue with the atomics in qemu-sh4:

  (sid-sh4-sbuild)root@epyc:/# cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  (sid-sh4-sbuild)root@epyc:/# gccgo-9 hello.go -o hello
  (sid-sh4-sbuild)root@epyc:/# ./hello 
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596

  goroutine 1 [running]:
          goroutine running on other thread; stack unavailable

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596
  (sid-sh4-sbuild)root@epyc:/#

  The same sample Go program runs fine on my SH7785LCR SH4 evaluation
  board:

  root@tirpitz:~> uname -a
  Linux tirpitz 3.16.7-ckt7 #8 PREEMPT Fri Oct 21 18:47:41 CEST 2016 sh4a GNU/Linux
  root@tirpitz:~> cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  root@tirpitz:~> gccgo-9 hello.go -o hello
  root@tirpitz:~> ./hello 
  hello world
  root@tirpitz:~>

  Please note: In order to be able to reproduce this, one also needs to
  revert commit 61dedf2af7 [2], otherwise the Go application crashes
  differently:

  (sid-sh4-sbuild)root@epyc:/# ./hello        
  Unhandled trap: 0x180
  pc=0x7e5f7f9e sr=0x00000000 pr=0x7ee3d582 fpscr=0x00080004
  spc=0x00000000 ssr=0x00000000 gbr=0x7e590480 vbr=0x00000000
  sgr=0x00000000 dbr=0x00000000 delayed_pc=0x7e5f7f60 fpul=0x00034f3b
  r0=0x008007d4 r1=0x00000000 r2=0xfffe0b2a r3=0x00000002
  r4=0x008006e4 r5=0x00872000 r6=0x00200000 r7=0x00000000
  r8=0x7f7bca7c r9=0x7fffebd4 r10=0x00800480 r11=0x7f7bc0f0
  r12=0x7f7a3fa4 r13=0x008004c0 r14=0x7f7b2238 r15=0x7fffebd0
  r16=0x00000000 r17=0x00000000 r18=0x00000000 r19=0x00000000
  r20=0x00000000 r21=0x00000000 r22=0x00000000 r23=0x00000000
  (sid-sh4-sbuild)root@epyc:/#

  > [1] https://bugs.launchpad.net/bugs/1738545
  > [2] https://bugs.launchpad.net/bugs/1796520

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1839325/+subscriptions

[Qemu-devel] [Bug 1839325] Re: Go programs crash on qemu-sh4 due to issues with atomics

[John Paul Adrian Glaubitz]

Thanks. I will report this to Go/gcc upstream.

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1839325

Title:
  Go programs crash on qemu-sh4 due to issues with atomics

Status in QEMU:
  New

Bug description:
  After #1738545 [1] was fixed, Go applications work fine on qemu-arm
  but still crash on qemu-sh4. From the backtrace, it looks like an
  issue with the atomics in qemu-sh4:

  (sid-sh4-sbuild)root@epyc:/# cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  (sid-sh4-sbuild)root@epyc:/# gccgo-9 hello.go -o hello
  (sid-sh4-sbuild)root@epyc:/# ./hello 
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596

  goroutine 1 [running]:
          goroutine running on other thread; stack unavailable

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596
  (sid-sh4-sbuild)root@epyc:/#

  The same sample Go program runs fine on my SH7785LCR SH4 evaluation
  board:

  root@tirpitz:~> uname -a
  Linux tirpitz 3.16.7-ckt7 #8 PREEMPT Fri Oct 21 18:47:41 CEST 2016 sh4a GNU/Linux
  root@tirpitz:~> cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  root@tirpitz:~> gccgo-9 hello.go -o hello
  root@tirpitz:~> ./hello 
  hello world
  root@tirpitz:~>

  Please note: In order to be able to reproduce this, one also needs to
  revert commit 61dedf2af7 [2], otherwise the Go application crashes
  differently:

  (sid-sh4-sbuild)root@epyc:/# ./hello        
  Unhandled trap: 0x180
  pc=0x7e5f7f9e sr=0x00000000 pr=0x7ee3d582 fpscr=0x00080004
  spc=0x00000000 ssr=0x00000000 gbr=0x7e590480 vbr=0x00000000
  sgr=0x00000000 dbr=0x00000000 delayed_pc=0x7e5f7f60 fpul=0x00034f3b
  r0=0x008007d4 r1=0x00000000 r2=0xfffe0b2a r3=0x00000002
  r4=0x008006e4 r5=0x00872000 r6=0x00200000 r7=0x00000000
  r8=0x7f7bca7c r9=0x7fffebd4 r10=0x00800480 r11=0x7f7bc0f0
  r12=0x7f7a3fa4 r13=0x008004c0 r14=0x7f7b2238 r15=0x7fffebd0
  r16=0x00000000 r17=0x00000000 r18=0x00000000 r19=0x00000000
  r20=0x00000000 r21=0x00000000 r22=0x00000000 r23=0x00000000
  (sid-sh4-sbuild)root@epyc:/#

  > [1] https://bugs.launchpad.net/bugs/1738545
  > [2] https://bugs.launchpad.net/bugs/1796520

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1839325/+subscriptions

[Bug 1839325] Re: Go programs crash on qemu-sh4 due to issues with atomics

[Peter Maydell]

I'm going to close this bug, since it's a problem with the gccgo
codegen, not a QEMU bug. (I'm interested in any response you get from
the go/gcc upstream folks, though.)


** Changed in: qemu
       Status: New => Invalid

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1839325

Title:
  Go programs crash on qemu-sh4 due to issues with atomics

Status in QEMU:
  Invalid

Bug description:
  After #1738545 [1] was fixed, Go applications work fine on qemu-arm
  but still crash on qemu-sh4. From the backtrace, it looks like an
  issue with the atomics in qemu-sh4:

  (sid-sh4-sbuild)root@epyc:/# cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  (sid-sh4-sbuild)root@epyc:/# gccgo-9 hello.go -o hello
  (sid-sh4-sbuild)root@epyc:/# ./hello 
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack
  panic: (        runtime runtime.errorString) (0x7f74527c,0x80a038)
  fatal error: panic on system stack

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596

  goroutine 1 [running]:
          goroutine running on other thread; stack unavailable

  runtime stack:
  runtime..z2finternal..z2fatomic.Load64
          ../../../src/libgo/go/runtime/internal/atomic/atomic.c:37
  runtime_mstart
          ../../../src/libgo/runtime/proc.c:596
  (sid-sh4-sbuild)root@epyc:/#

  The same sample Go program runs fine on my SH7785LCR SH4 evaluation
  board:

  root@tirpitz:~> uname -a
  Linux tirpitz 3.16.7-ckt7 #8 PREEMPT Fri Oct 21 18:47:41 CEST 2016 sh4a GNU/Linux
  root@tirpitz:~> cat hello.go
  package main

  import "fmt"

  func main() {
        fmt.Println("hello world")
  }

  root@tirpitz:~> gccgo-9 hello.go -o hello
  root@tirpitz:~> ./hello 
  hello world
  root@tirpitz:~>

  Please note: In order to be able to reproduce this, one also needs to
  revert commit 61dedf2af7 [2], otherwise the Go application crashes
  differently:

  (sid-sh4-sbuild)root@epyc:/# ./hello        
  Unhandled trap: 0x180
  pc=0x7e5f7f9e sr=0x00000000 pr=0x7ee3d582 fpscr=0x00080004
  spc=0x00000000 ssr=0x00000000 gbr=0x7e590480 vbr=0x00000000
  sgr=0x00000000 dbr=0x00000000 delayed_pc=0x7e5f7f60 fpul=0x00034f3b
  r0=0x008007d4 r1=0x00000000 r2=0xfffe0b2a r3=0x00000002
  r4=0x008006e4 r5=0x00872000 r6=0x00200000 r7=0x00000000
  r8=0x7f7bca7c r9=0x7fffebd4 r10=0x00800480 r11=0x7f7bc0f0
  r12=0x7f7a3fa4 r13=0x008004c0 r14=0x7f7b2238 r15=0x7fffebd0
  r16=0x00000000 r17=0x00000000 r18=0x00000000 r19=0x00000000
  r20=0x00000000 r21=0x00000000 r22=0x00000000 r23=0x00000000
  (sid-sh4-sbuild)root@epyc:/#

  > [1] https://bugs.launchpad.net/bugs/1738545
  > [2] https://bugs.launchpad.net/bugs/1796520

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1839325/+subscriptions