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[Bug 1856837] Re: qemu 4.2.0 arm segmentation fault with gcc 9.2


From: Peter Maydell
Subject: [Bug 1856837] Re: qemu 4.2.0 arm segmentation fault with gcc 9.2
Date: Thu, 19 Dec 2019 15:01:02 -0000

Can you provide a repro case (attach binary/etc to the bug) so we can
investigate?

Note that QEMU will produce that segfault message both for bugs in QEMU
(where it unexpectedly segfaults) but also for bugs in the guest binary
itself where we're correctly emulating "guest did something causing a
segfault".


** Tags added: arm

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https://bugs.launchpad.net/bugs/1856837

Title:
  qemu 4.2.0 arm  segmentation fault with gcc 9.2

Status in QEMU:
  New

Bug description:
  As discussed with f4bug yesterday on IRC here comes the bug
  description.

  I'm building/configured qemu-4.2.0 on an x86_64 (gcc (Debian
  6.3.0-18+deb9u1) 6.3.0 20170516) with target-list "arm-softmmu,arm-
  linux-user" and debug enabled. I use the arm-linux-user variant,
  "qemu-arm".

  Then i'm trying to cross-compile (arm gcc) an old version of googles
  v8 (as i need this version of the lib for binary compatibility) which
  uses qemu during build.

  It worked with gcc 5.4.0 but not with 9.2.0. I also tried with 6.5.0,
  7.4.0 and 8.3.0 but those are also causing the same segmentation
  fault.

  The executed command wich breaks qemu is:

   qemu-arm /tmp/build/out/arm.release/mksnapshot.arm --log-snapshot-
  positions --logfile
  /tmp/build/out/arm.release/obj.host/v8_snapshot/geni/snapshot.log
  --random-seed 314159265 /tmp/build/out/arm.release/obj.host/v8_snap

  The printed error message is:

  ARMv7=1 VFP3=1 VFP32DREGS=1 NEON=0 SUDIV=0 UNALIGNED_ACCESSES=1 
MOVW_MOVT_IMMEDIATE_LOADS=0 USE_EABI_HARDFLOAT=1
  qemu: uncaught target signal 11 (Segmentation fault) - core dumped

  Calling qemu with gdb gives the following information:

   Thread 1 "qemu-arm" received signal SIGSEGV, Segmentation fault.
   0x0000555555d63d11 in static_code_gen_buffer ()

  and

   (gdb) bt
   #0  0x0000555555d63d11 in static_code_gen_buffer ()
   #1  0x0000555555628d58 in cpu_tb_exec (itb=<optimized out>, 
cpu=0x555557c33930) at 
   /tmp/build/qemu/accel/tcg/cpu-exec.c:172
   #2  cpu_loop_exec_tb (tb_exit=<synthetic pointer>, last_tb=<synthetic 
pointer>, tb=<optimized out>, 
   cpu=0x555557c33930) at /tmp/build/qemu/accel/tcg/cpu-exec.c:618
   #3  cpu_exec (cpu=cpu@entry=0x555557c2b660) at 
/tmp/build/qemu/accel/tcg/cpu-exec.c:731
   #4  0x0000555555661578 in cpu_loop (env=0x555557c33930) at 
/tmp/build/qemu/linux-user/arm/cpu_loop.c:219
  #5  0x00005555555d6d76 in main (argc=<optimized out>, argv=<optimized out>, 
envp=<optimized out>) at /tmp/build/qemu/linux-user/main.c:865

  Calling qemu-arm with debug switch "-d in_asm,int,op_opt" shows the
  log in the attached file.

  Thanks for any hints!
  Fabian

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