[Bug 1913913] Re: i386-linux-user returns -1 in sigcontext->trapno

[Launchpad Bug Tracker]

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1913913

Title:
  i386-linux-user returns -1 in sigcontext->trapno

Status in QEMU:
  Expired

Bug description:
  QEMU development version, git commit
  74208cd252c5da9d867270a178799abd802b9338. Behaviour has been noted in
  5.2.0 generally.

  Certain 16-bit windows programs crash WINE under QEMU linux-user with:

  0084:err:seh:segv_handler Got unexpected trap -1
  wine: Unhandled illegal instruction at address 00006D65 (thread 0084), 
starting debugger...

  They run correctly on native i386.

  Upon further inspection,it becomes clear these programs are failing at
  addresses where they are making DOS calls (int 21h ie CD 21 for
  instance).

  It is also clear that WINE is expecting an exception/signal at this
  point, to patch in the actual int21h handling code inside WINE.

  However, wine uses sigcontext output extensively to do its structured
  exception handling. sigcontext->trapno being set to -1 seems to
  confuse it, causing it to treat the exception as an actual unhandled
  error.

  I do not know if exception_index is being left at -1 due to the case
  of privileged instructions being executed in 16-bit ldts not being
  handled specifically, or if there is some other illegal instruction
  case causing this.

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