cmd/dist: binary distribution faults on software fp mismatch

[gopherbot]

by pj@isomero.us:

1. What is a short input program that triggers the error?
http://play.golang.org/p/c6IGPOs4Ra

2. What is the full compiler output?
<unknown line number>: internal compiler error: fault

3. What version of the compiler are you using?  (Run it with the -V flag.)
5g version devel +5b367120d592 Thu Sep 19 17:12:00 2013 +1000

[remyoudompheng]

Comment 1:

Please explain:
- what is the command you are running ?
- how much memory do you have available ?
- what is the system you are running 5g on ?

[gopherbot]

Comment 2 by pj@isomero.us:

- What is the command you are running?
"go build"
- How much memory do you have available?
350 MB RAM free / 512 MB RAM total.
- What is the system you are running 5g on?
BeagleBone Black

[remyoudompheng]

Comment 3:

Please run go build -x

[gopherbot]

Comment 4 by pj@isomero.us:

$ go build -x
WORK=/tmp/go-build771135909
mkdir -p $WORK/_/home/root/test/_obj/
cd /home/root/test
/usr/local/go/pkg/tool/linux_arm/5g -o $WORK/_/home/root/test/_obj/_go_.5 -p
_/home/root/test -complete -D _/home/root/test -I $WORK ./list.go
# _/home/root/test
<unknown line number>: internal compiler error: fault

[remyoudompheng]

Comment 5:

Does it also happen if you just say:
/usr/local/go/pkg/tool/linux_arm/5g list.go ?
If so, can you run it under gdb and obtain a backtrace ?

[gopherbot]

Comment 6 by pj@isomero.us:

(gdb) run list.go
Starting program: /usr/local/go/pkg/tool/linux_arm/5g list.go
Program received signal SIGSEGV, Segmentation fault.
0xb6f7e364 in frexpl () from /lib/libm.so.6
(gdb) bt
#0  0xb6f7e364 in frexpl () from /lib/libm.so.6
#1  0x00033060 in mpmovecflt (a=a@entry=0xbefff950, c=10)
    at /tmp/bindist030113356/go/src/cmd/gc/mparith3.c:273
#2  0x00030be8 in mpmulcflt (a=a@entry=0x8d1f8, c=<optimized out>)
    at /tmp/bindist030113356/go/src/cmd/gc/mparith1.c:119
#3  0x000311f0 in mpatoflt (a=0x8d1f8, as=as@entry=0x651c8 "33554431p103")
    at /tmp/bindist030113356/go/src/cmd/gc/mparith1.c:375
#4  0x0001eaf8 in typeinit ()
    at /tmp/bindist030113356/go/src/cmd/gc/align.c:576
#5  0x0002f984 in p9main (argc=8, argv=0x8c218)
    at /tmp/bindist030113356/go/src/cmd/gc/lex.c:341
#6  0x00008ef4 in main (argc=<optimized out>, argv=<optimized out>)
    at /tmp/bindist030113356/go/src/lib9/main.c:55

[remyoudompheng]

Comment 7:

Can you also say "disas" and "info reg" in addition to backtrace ?

[remyoudompheng]

Comment 8:

Also explain: how did you install this version of Go? (from Mercurial? from Go 1.2rc1
binary distribution?) and what is your operating system flavour.

[gopherbot]

Comment 9 by pj@isomero.us:

(gdb) disas
Dump of assembler code for function frexpl:
   0xb6f7e348 <+0>:   movw    r12, #65535 ; 0xffff
   0xb6f7e34c <+4>:   bic r3, r1, #-2147483648    ; 0x80000000
   0xb6f7e350 <+8>:   movt    r12, #32751 ; 0x7fef
   0xb6f7e354 <+12>:  vmov    d16, r0, r1
   0xb6f7e358 <+16>:  cmp r3, r12
   0xb6f7e35c <+20>:  push    {r4}        ; (str r4, [sp, #-4]!)
   0xb6f7e360 <+24>:  mov r4, #0
=> 0xb6f7e364 <+28>:   str r4, [r2]
   0xb6f7e368 <+32>:  bgt 0xb6f7e3b8 <frexpl+112>
   0xb6f7e36c <+36>:  orrs    r12, r3, r0
   0xb6f7e370 <+40>:  beq 0xb6f7e3b8 <frexpl+112>
   0xb6f7e374 <+44>:  cmp r3, #1048576    ; 0x100000
   0xb6f7e378 <+48>:  vldrlt  d17, [pc, #72]  ; 0xb6f7e3c8 <frexpl+128>
   0xb6f7e37c <+52>:  vmullt.f64  d16, d16, d17
   0xb6f7e380 <+56>:  mvnlt   r4, #53 ; 0x35
   0xb6f7e384 <+60>:  vmovlt  r0, r1, d16
   0xb6f7e388 <+64>:  biclt   r3, r1, #-2147483648    ; 0x80000000
   0xb6f7e38c <+68>:  bic r12, r1, #2130706432    ; 0x7f000000
   0xb6f7e390 <+72>:  vmov    r0, r1, d16
   0xb6f7e394 <+76>:  bic r12, r12, #15728640 ; 0xf00000
   0xb6f7e398 <+80>:  orr r12, r12, #1069547520   ; 0x3fc00000
   0xb6f7e39c <+84>:  asr r3, r3, #20
---Type <return> to continue, or q <return> to quit---
   0xb6f7e3a0 <+88>:  orr r1, r12, #2097152   ; 0x200000
   0xb6f7e3a4 <+92>:  sub r3, r3, #1020   ; 0x3fc
   0xb6f7e3a8 <+96>:  sub r3, r3, #2
   0xb6f7e3ac <+100>: add r4, r3, r4
   0xb6f7e3b0 <+104>: str r4, [r2]
   0xb6f7e3b4 <+108>: vmov    d16, r0, r1
   0xb6f7e3b8 <+112>: vmov    r0, r1, d16
   0xb6f7e3bc <+116>: ldmfd   sp!, {r4}
   0xb6f7e3c0 <+120>: bx  lr
   0xb6f7e3c4 <+124>: nop {0}
   0xb6f7e3c8 <+128>: andeq   r0, r0, r0
   0xb6f7e3cc <+132>: cmpmi   r0, #0
End of assembler dump.
(gdb) info reg
r0             0xbefff92c   3204446508
r1             0x0  0
r2             0x0  0
r3             0x0  0
r4             0x0  0
r5             0x0  0
r6             0x8d1f8  578040
r7             0x0  0
r8             0x651c9  414153
r9             0x33 51
r10            0xa  10
r11            0x0  0
r12            0x7fefffff   2146435071
sp             0xbefff924   0xbefff924
lr             0x33060  208992
pc             0xb6f7e364   0xb6f7e364 <frexpl+28>
cpsr           0x80000010   -2147483632
This is with Dave Cheney's ARM tarball: http://dave.cheney.net/unofficial-arm-tarballs
This is on Angstrom (32-bit Linux).

[remyoudompheng]

Comment 10:

I think you have a calling convention mismatch. Please show the disasm of the calling
frame.

[gopherbot]

Comment 11 by pj@isomero.us:

Sorry, I'm rather new to gdb. How exactly would I do that?

[remyoudompheng]

Comment 12:

Say "up" before saying "disas".

[gopherbot]

Comment 13 by pj@isomero.us:

(gdb) run list.go
Starting program: /usr/local/go/pkg/tool/linux_arm/5g list.go
Program received signal SIGSEGV, Segmentation fault.
0xb6f7e364 in frexpl () from /lib/libm.so.6
(gdb) up
#1  0x00033060 in mpmovecflt (a=a@entry=0xbefff950, c=10)
    at /tmp/bindist030113356/go/src/cmd/gc/mparith3.c:273
273 /tmp/bindist030113356/go/src/cmd/gc/mparith3.c: No such file or directory.
(gdb) disas
Dump of assembler code for function mpmovecflt:
   0x00033008 <+0>:   push    {r4, r5, r6, lr}
   0x0003300c <+4>:   vpush   {d8-d9}
   0x00033010 <+8>:   vmov.f64    d8, d0
   0x00033014 <+12>:  sub sp, sp, #8
   0x00033018 <+16>:  mov r2, #0
   0x0003301c <+20>:  mov r3, #0
   0x00033020 <+24>:  mov r4, r0
   0x00033024 <+28>:  bl  0x327ac <mpmovecfix>
   0x00033028 <+32>:  mov r5, #0
   0x0003302c <+36>:  vcmp.f64    d8, #0.0
   0x00033030 <+40>:  strh    r5, [r4, #68]   ; 0x44
   0x00033034 <+44>:  vmrs    APSR_nzcv, fpscr
   0x00033038 <+48>:  beq 0x330c4 <mpmovecflt+188>
   0x0003303c <+52>:  vcmpe.f64   d8, #0.0
   0x00033040 <+56>:  vmrs    APSR_nzcv, fpscr
   0x00033044 <+60>:  movmi   r3, #1
   0x00033048 <+64>:  vnegmi.f64  d0, d8
   0x0003304c <+68>:  strbmi  r3, [r4, #64]   ; 0x40
   0x00033050 <+72>:  vmovpl.f64  d0, d8
   0x00033054 <+76>:  add r0, sp, #4
   0x00033058 <+80>:  vldr    d9, [pc, #120]  ; 0x330d8 <mpmovecflt+208>
   0x0003305c <+84>:  bl  0x8d5c
---Type <return> to continue, or q <return> to quit---
=> 0x00033060 <+88>:   ldrh    r6, [sp, #4]
   0x00033064 <+92>:  str r5, [sp, #4]
   0x00033068 <+96>:  mov r5, #1
   0x0003306c <+100>: vmov.f64    d8, d0
   0x00033070 <+104>: b   0x3308c <mpmovecflt+132>
   0x00033074 <+108>: bl  0x31950 <mpshiftfix>
   0x00033078 <+112>: str r5, [sp, #4]
   0x0003307c <+116>: add r5, r5, #1
   0x00033080 <+120>: cmp r5, #11
   0x00033084 <+124>: beq 0x330c4 <mpmovecflt+188>
   0x00033088 <+128>: ldrh    r6, [r4, #68]   ; 0x44
   0x0003308c <+132>: vmul.f64    d8, d8, d9
   0x00033090 <+136>: sub r6, r6, #29
   0x00033094 <+140>: vmov.f64    d0, d8
   0x00033098 <+144>: bl  0x8c54
   0x0003309c <+148>: mov r0, r4
   0x000330a0 <+152>: mov r1, #29
   0x000330a4 <+156>: strh    r6, [r4, #68]   ; 0x44
   0x000330a8 <+160>: vcvt.s32.f64    s0, d0
   0x000330ac <+164>: vcvt.f64.s32    d7, s0
   0x000330b0 <+168>: vstr    s0, [r4]
   0x000330b4 <+172>: vsub.f64    d8, d8, d7
   0x000330b8 <+176>: vcmp.f64    d8, #0.0
---Type <return> to continue, or q <return> to quit---
   0x000330bc <+180>: vmrs    APSR_nzcv, fpscr
   0x000330c0 <+184>: bne 0x33074 <mpmovecflt+108>
   0x000330c4 <+188>: mov r0, r4
   0x000330c8 <+192>: add sp, sp, #8
   0x000330cc <+196>: vpop    {d8-d9}
   0x000330d0 <+200>: pop {r4, r5, r6, lr}
   0x000330d4 <+204>: b   0x32aac <mpnorm>
   0x000330d8 <+208>: andeq   r0, r0, r0
   0x000330dc <+212>: bicmi   r0, r0, r0
End of assembler dump.

[remyoudompheng]

Comment 14:

I think that your system uses the soft float ABI while Dave's binary is hard-float
(armhf), thus incompatible. I'm not sure how to confirm the hypothesis. 
Try running "readelf -A" on /lib/libm.so.6 and on /usr/local/go/pkg/tool/linux_arm/5g

[davecheney]

Comment 15:

I think Remy is right on the money, you will probably have to compile go on your BBB, it
takes ~45 mins for ./all.bash, less than half of that if you run ./make,bash only.

Labels changed: removed go1.2maybe.