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

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

[Dirk A Niggemann]

Public bug reported:

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.

** Affects: qemu
     Importance: Undecided
         Status: New

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

Status in QEMU:
  New

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

[Dirk A Niggemann]

I have identified the core issue:

Synchronous exceptions/traps in linux-user/i386/cpu_loop.c are handled as a return value from cpu_exec().
cpu_exec() resets exception_index to -1 in  cpu_handle_exception()

This means that queue_signal() (called from gen_signal() in the cpu
loop) does not store the actual  CPU trap value anywhere.

If we abuse env->exception_nr to store the trapnr, and retrieve it from
there in setup_sigcontext() in linux-user/i386/signal.c instead of using
exception_index (which will be set to -1 for all synchronous excptions).

The main issue is if this breaks asynchronous signals, and under what
conditions exception_nr should be set to -1.

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

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

Status in QEMU:
  New

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

[Thomas Huth]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting the bug state to "Incomplete" now.

If the bug has already been fixed in the latest upstream version of QEMU,
then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here is still
valid, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:

    https://gitlab.com/qemu-project/qemu/-/issues

and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" or "Confirmed" within the next 60 days (other-
wise it will get closed as "Expired"). We will then eventually migrate
the ticket automatically to the new system (but you won't be the reporter
of the bug in the new system and thus you won't get notified on changes
anymore).

Thank you and sorry for the inconvenience.


** Tags added: linux-user tcg

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

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

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

Status in QEMU:
  Incomplete

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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https://bugs.launchpad.net/qemu/+bug/1913913/+subscriptions

[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.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1913913/+subscriptions