llvm self-tests looping(?)

To: current-users%NetBSD.org@localhost
Subject: llvm self-tests looping(?)
From: Havard Eidnes <he%NetBSD.org@localhost>
Date: Sun, 01 Apr 2018 16:53:37 +0200 (CEST)
Hi,

I decided it might be a good idea to run the self-tests in llvm
5.0.1 on powerpc.  However, after the test and utilities are
built, it appears to spin while doing the first test.  The run
log shows:

[100%] Built target LLVMHello_exports
[100%] Built target LLVMHello
Scanning dependencies of target check-llvm
[100%] Running the LLVM regression tests
-- Testing: 21465 tests, 1 threads --
Testing: 0 ..

and the process is spinning consuming CPU (well, it's stopped in
the debugger here):

  PID USERNAME PRI NICE   SIZE   RES STATE      TIME   WCPU    CPU COMMAND
    0 root     126    0     0K   22M pgdaemon 600:47  0.00%  0.00% [system]
19597 root      28    4    43M   15M STOP     306:27  0.00%  0.00% SupportTests

and the debugger points towards libexecinfo:

ambrosia# gdb -q ./work/build/unittests/Support/SupportTests
Reading symbols from ./work/build/unittests/Support/SupportTests...(no debugging symbols found)...done.
(gdb) attach 19597
Attaching to program: /usr/pkgsrc/lang/llvm/work/build/unittests/Support/SupportTests, process 19597
Couldn't get registers: Device busy.
Couldn't get registers: Device busy.
(gdb) Reading symbols from /usr/lib/libpthread.so.1...(no debugging symbols found)...done.
Reading symbols from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so...(no debugging symbols found)...done.
Reading symbols from /usr/lib/librt.so.1...(no debugging symbols found)...done.
Reading symbols from /usr/lib/libexecinfo.so.0...(no debugging symbols found)...done.
Reading symbols from /usr/lib/libterminfo.so.1...(no debugging symbols found)...done.
Reading symbols from /usr/lib/libz.so.1...(no debugging symbols found)...done.
Reading symbols from /usr/lib/libstdc++.so.7...(no debugging symbols found)...done.
Reading symbols from /usr/lib/libm.so.0...(no debugging symbols found)...done.
Reading symbols from /usr/lib/libgcc_s.so.1...(no debugging symbols found)...done.
Reading symbols from /usr/lib/libc.so.12...(no debugging symbols found)...done.
Reading symbols from /usr/lib/libedit.so.3...(no debugging symbols found)...done.
Reading symbols from /usr/lib/libelf.so.2...(no debugging symbols found)...done.
Reading symbols from /usr/libexec/ld.elf_so...(no debugging symbols found)...done.
[Switching to LWP 1]
0xfc1d3fcc in ?? () from /usr/lib/libexecinfo.so.0

(gdb) where
#0  0xfc1d3fcc in ?? () from /usr/lib/libexecinfo.so.0
#1  0xfc1d4514 in ?? () from /usr/lib/libexecinfo.so.0
#2  0xfc1d53e0 in _Unwind_Backtrace () from /usr/lib/libexecinfo.so.0
#3  0xfc1d128c in backtrace () from /usr/lib/libexecinfo.so.0
#4  0xfc673ac4 in llvm::sys::PrintStackTrace(llvm::raw_ostream&) ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#5  0xfc673e4c in PrintStackTraceSignalHandler(void*) ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#6  0xfc671c08 in llvm::sys::RunSignalHandlers() ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#7  0xfc671e88 in SignalHandler(int) ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#8  0xfbe2af58 in opendir () from /usr/lib/libc.so.12
Backtrace stopped: frame did not save the PC
(gdb) i thread
  Id   Target Id         Frame 
* 1    LWP 1             0xfbeb4c4c in memcpy () from /usr/lib/libc.so.12
(gdb)

and an earlier backtrace of the same process gave

(gdb) where
#0  0xfbeb4c4c in memcpy () from /usr/lib/libc.so.12
#1  0xfc1d2c20 in ?? () from /usr/lib/libexecinfo.so.0
#2  0xfc1d3470 in ?? () from /usr/lib/libexecinfo.so.0
#3  0xfc1d52e8 in _Unwind_Backtrace () from /usr/lib/libexecinfo.so.0
#4  0xfc1d128c in backtrace () from /usr/lib/libexecinfo.so.0
#5  0xfc673ac4 in llvm::sys::PrintStackTrace(llvm::raw_ostream&) ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#6  0xfc673e4c in PrintStackTraceSignalHandler(void*) ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#7  0xfc671c08 in llvm::sys::RunSignalHandlers() ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#8  0xfc671e88 in SignalHandler(int) ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#9  0xfbe2af58 in opendir () from /usr/lib/libc.so.12
Backtrace stopped: frame did not save the PC
(gdb) 

Setting a breakpoint on the next instruction in backtrace():

(gdb) x/i 0xfc1d128c
   0xfc1d128c <backtrace+60>:   lwz     r3,16(r1)
(gdb) x/i backtrace
   0xfc1d1250 <backtrace>:      stwu    r1,-48(r1)
(gdb) x/20i
   0xfc1d1254 <backtrace+4>:    mflr    r0
   0xfc1d1258 <backtrace+8>:    bcl     20,4*cr7+so,0xfc1d125c <backtrace+12>
   0xfc1d125c <backtrace+12>:   li      r9,-1
   0xfc1d1260 <backtrace+16>:   stw     r30,40(r1)
   0xfc1d1264 <backtrace+20>:   mflr    r30
   0xfc1d1268 <backtrace+24>:   stw     r3,8(r1)
   0xfc1d126c <backtrace+28>:   stw     r4,12(r1)
   0xfc1d1270 <backtrace+32>:   addi    r4,r1,8
   0xfc1d1274 <backtrace+36>:   addis   r30,r30,2
   0xfc1d1278 <backtrace+40>:   stw     r9,16(r1)
   0xfc1d127c <backtrace+44>:   addi    r30,r30,-448
   0xfc1d1280 <backtrace+48>:   stw     r0,52(r1)
   0xfc1d1284 <backtrace+52>:   lwz     r3,-32768(r30)
   0xfc1d1288 <backtrace+56>:
    bl      0xfc1d7320 <00008000.got2.plt_pic32._Unwind_Backtrace>
   0xfc1d128c <backtrace+60>:   lwz     r3,16(r1)
   0xfc1d1290 <backtrace+64>:   li      r9,-3
   0xfc1d1294 <backtrace+68>:   addi    r10,r3,-1
   0xfc1d1298 <backtrace+72>:   cmplw   cr7,r10,r9
   0xfc1d129c <backtrace+76>:   bgt     cr7,0xfc1d12b4 <backtrace+100>
   0xfc1d12a0 <backtrace+80>:   lwz     r8,8(r1)
(gdb) 
   0xfc1d12a4 <backtrace+84>:   rlwinm  r9,r10,2,0,29
   0xfc1d12a8 <backtrace+88>:   li      r7,0
   0xfc1d12ac <backtrace+92>:   mr      r3,r10
   0xfc1d12b0 <backtrace+96>:   stwx    r7,r8,r9
   0xfc1d12b4 <backtrace+100>:  lwz     r0,52(r1)
   0xfc1d12b8 <backtrace+104>:  lwz     r30,40(r1)
   0xfc1d12bc <backtrace+108>:  mtlr    r0
   0xfc1d12c0 <backtrace+112>:  addi    r1,r1,48
   0xfc1d12c4 <backtrace+116>:  blr
...
(gdb) b *0xfc1d128c
Breakpoint 1 at 0xfc1d128c
(gdb) cont
Continuing.

makes it continue to spin and never hit the breakpoint.

So ... is this a lack of robustness in libexecinfo?

load averages:  0.95,  0.65,  0.86;               up 116+04:14:37           16:46:06
63 processes: 1 runnable, 61 sleeping, 1 on CPU
CPU states:  0.2% user, 99.0% nice,  0.6% system,  0.2% interrupt,  0.0% idle
Memory: 173M Act, 276M Inact, 8832K Wired, 57M Exec, 271M File, 443M Free
Swap: 1300M Total, 21M Used, 1279M Free

  PID USERNAME PRI NICE   SIZE   RES STATE      TIME   WCPU    CPU COMMAND
19597 root      21    4    43M   15M RUN      307:29 92.38% 92.38% SupportTests
    0 root     126    0     0K   22M pgdaemon 600:48  0.00%  0.00% [system]

Also, putting a breakpoint in _Unwind_Backtrace also doesn't hit:

   0xfc1d53e0 <_Unwind_Backtrace+460>:
    b       0xfc1d52dc <_Unwind_Backtrace+200>
   0xfc1d53e4 <_Unwind_Backtrace+464>:  li      r3,5
   0xfc1d53e8 <_Unwind_Backtrace+468>:
    b       0xfc1d5314 <_Unwind_Backtrace+256>
   0xfc1d53ec:  stwu    r1,-48(r1)
   0xfc1d53f0:  mflr    r0
   0xfc1d53f4:  stw     r31,44(r1)
(gdb) b *0xfc1d53e4
Breakpoint 2 at 0xfc1d53e4
(gdb) where
#0  0xfc1d3558 in ?? () from /usr/lib/libexecinfo.so.0
#1  0xfc1d52e8 in _Unwind_Backtrace () from /usr/lib/libexecinfo.so.0
#2  0xfc1d128c in backtrace () from /usr/lib/libexecinfo.so.0
#3  0xfc673ac4 in llvm::sys::PrintStackTrace(llvm::raw_ostream&) ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#4  0xfc673e4c in PrintStackTraceSignalHandler(void*) ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#5  0xfc671c08 in llvm::sys::RunSignalHandlers() ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#6  0xfc671e88 in SignalHandler(int) ()
   from /usr/pkgsrc/lang/llvm/work/build/lib/libLLVM-5.0.so
#7  0xfbe2af58 in opendir () from /usr/lib/libc.so.12
Backtrace stopped: frame did not save the PC
(gdb) cont
Continuing.

...and no drop to gdb again.

And some of the internal functions in libexecinfo are apparently
static, so not present in the symbol table for display in the
debugger, making debugging all that much harder.

Sigh!

Hints, anyone?

Regards,

- Håvard
Follow-Ups:
- Re: llvm self-tests looping(?)
  - From: Havard Eidnes
- Re: llvm self-tests looping(?)
  - From: Kamil Rytarowski
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