[Bug 1915682] Re: i386-linux-user wine exception regression tests fail

[Dirk A Niggemann]

That was a complete misdiaagnsis. The IRET works fine in user space, at
the lowest privlege level.

The wrong thread is not restarted. The correct thread continues
execution, at the correct address, but with the wrong thread-local data.

Thread-local data is accessed via the segment loaded in the fs register
in wine. The segment selector is set the same in each thread, but each
thread should have a unique GDT entry pointing to its thread-local data.

The issue is that clone() copies the pointer reference to the process's
GDT without creating a new GDT area. All threads wind up sharing the
same GDT. As the selector is the same, all threads share the same threa-
local data. Oddly enough, this has fewer ill effects than excpected.
Unless SEH (Structured Exception Handling) is invoked, at which point
threads start unwinding the stack frames of other threads...

Copying the GDT during clone() results in a workig system with correct
exception handling.

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https://bugs.launchpad.net/bugs/1915682

Title:
  i386-linux-user wine exception regression tests fail

Status in QEMU:
  New

Bug description:
  When trying to run wine (latest devel from git) regression tests for
  ntdll in a statically linked qemu-i386 (commit
  392b9a74b9b621c52d05e37bc6f41f1bbab5c6f8) on arm32 (raspberry pi 4) in
  a debian buster chroot, the exception tests fail at the first test
  with an infinite exception loop.

  WINEDEBUG=+seh wine wine/dlls/ntdll/tests/ntdll_test.exe exception

  
  Working x86_64 system running 32-bit code

  0024:warn:seh:dispatch_exception EXCEPTION_ACCESS_VIOLATION exception 
(code=c0000005) raised
  0024:trace:seh:dispatch_exception  eax=00000000 ebx=7ffc2000 ecx=004e0ef4 
edx=003c0004 esi=003c0000 edi=00000000
  0024:trace:seh:dispatch_exception  ebp=0085fa08 esp=0085f9ac cs=0023 ds=002b 
es=002b fs=0063 gs=006b flags=00010246
  0024:trace:seh:call_vectored_handlers calling handler at 7B00B460 
code=c0000005 flags=0
  0024:trace:seh:call_vectored_handlers handler at 7B00B460 returned 0
  0024:trace:seh:call_stack_handlers calling handler at 004178B0 code=c0000005 
flags=0
  0024:trace:seh:call_stack_handlers handler at 004178B0 returned 0
  0024:trace:seh:dispatch_exception  call_stack_handlers continuing
  0024:trace:seh:NtGetContextThread 0xfffffffe: dr0=42424240 dr1=00000000 
dr2=126bb070 dr3=0badbad0 dr6=00000000 dr7=ffff0115

  
  Non-working qemu

  0024:warn:seh:dispatch_exception EXCEPTION_ACCESS_VIOLATION exception 
(code=c0000005) raised
  0024:trace:seh:dispatch_exception  eax=00000000 ebx=3ffe2000 ecx=004e0ef4 
edx=003c0004 esi=003c0000 edi=00000000
  0024:trace:seh:dispatch_exception  ebp=0085fa08 esp=0085f9ac cs=0023 ds=002b 
es=002b fs=003b gs=0033 flags=00000246
  0024:trace:seh:call_vectored_handlers calling handler at 7B00B460 
code=c0000005 flags=0
  0024:trace:seh:call_vectored_handlers handler at 7B00B460 returned 0
  0024:trace:seh:call_stack_handlers calling handler at 004178B0 code=c0000005 
flags=0
  0024:trace:seh:call_stack_handlers handler at 004178B0 returned 0
  0024:trace:seh:dispatch_exception  call_stack_handlers continuing
  0024:trace:seh:dispatch_exception  call_stack_handlers ret status = 0
  0024:trace:seh:dispatch_exception code=0 flags=1 addr=7BC2389C ip=7bc2389c 
tid=0024

  The non-working verion is never managing to set the CPU context using
  NtContinue/SetContextThread back to the correct running thread stack
  and IP. It executes as if the context restore just returns to the
  function that called NtContinue() (dispatch_exception(), not the
  function that raised the exception or one of its parent exception
  handlers).

  It looks like NtSetContextThread(), specifically the asm function
  set_full_cpu_context() is being handled incorrectly.

  wine code below. note interesting use of iret with no previous
  interrupt call. The exception handler is called with a jmp.

  /***********************************************************************
   *           set_full_cpu_context
   *
   * Set the new CPU context.
   */
  extern void set_full_cpu_context( const CONTEXT *context );
  __ASM_GLOBAL_FUNC( set_full_cpu_context,
                     "movl $0,%fs:0x1f8\n\t"     /* 
x86_thread_data()->syscall_frame = NULL */
                     "movl 4(%esp),%ecx\n\t"
                     "movw 0x8c(%ecx),%gs\n\t"  /* SegGs */
                     "movw 0x90(%ecx),%fs\n\t"  /* SegFs */
                     "movw 0x94(%ecx),%es\n\t"  /* SegEs */
                     "movl 0x9c(%ecx),%edi\n\t" /* Edi */
                     "movl 0xa0(%ecx),%esi\n\t" /* Esi */
                     "movl 0xa4(%ecx),%ebx\n\t" /* Ebx */
                     "movl 0xb4(%ecx),%ebp\n\t" /* Ebp */
                     "movw %ss,%ax\n\t"
                     "cmpw 0xc8(%ecx),%ax\n\t"  /* SegSs */
                     "jne 1f\n\t"
                     /* As soon as we have switched stacks the context 
structure could
                      * be invalid (when signal handlers are executed for 
example). Copy
                      * values on the target stack before changing ESP. */
                     "movl 0xc4(%ecx),%eax\n\t" /* Esp */
                     "leal -4*4(%eax),%eax\n\t"
                     "movl 0xc0(%ecx),%edx\n\t" /* EFlags */
                     ".byte 0x36\n\t"
                     "movl %edx,3*4(%eax)\n\t"
                     "movl 0xbc(%ecx),%edx\n\t" /* SegCs */
                     ".byte 0x36\n\t"
                     "movl %edx,2*4(%eax)\n\t"
                     "movl 0xb8(%ecx),%edx\n\t" /* Eip */
                     ".byte 0x36\n\t"
                     "movl %edx,1*4(%eax)\n\t"
                     "movl 0xb0(%ecx),%edx\n\t" /* Eax */
                     ".byte 0x36\n\t"
                     "movl %edx,0*4(%eax)\n\t"
                     "pushl 0x98(%ecx)\n\t"     /* SegDs */
                     "movl 0xa8(%ecx),%edx\n\t" /* Edx */
                     "movl 0xac(%ecx),%ecx\n\t" /* Ecx */
                     "popl %ds\n\t"
                     "movl %eax,%esp\n\t"
                     "popl %eax\n\t"
                     "iret\n"
                     /* Restore the context when the stack segment changes. We 
can't use
                      * the same code as above because we do not know if the 
stack segment
                      * is 16 or 32 bit, and 'movl' will throw an exception 
when we try to
                      * access memory above the limit. */
                     "1:\n\t"
                     "movl 0xa8(%ecx),%edx\n\t" /* Edx */
                     "movl 0xb0(%ecx),%eax\n\t" /* Eax */
                     "movw 0xc8(%ecx),%ss\n\t"  /* SegSs */
                     "movl 0xc4(%ecx),%esp\n\t" /* Esp */
                     "pushl 0xc0(%ecx)\n\t"     /* EFlags */
                     "pushl 0xbc(%ecx)\n\t"     /* SegCs */
                     "pushl 0xb8(%ecx)\n\t"     /* Eip */
                     "pushl 0x98(%ecx)\n\t"     /* SegDs */
                     "movl 0xac(%ecx),%ecx\n\t" /* Ecx */
                     "popl %ds\n\t"
                     "iret" )

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