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[Bug 1915682] Re: i386-linux-user wine exception regression tests fail
From: |
Dirk A Niggemann |
Subject: |
[Bug 1915682] Re: i386-linux-user wine exception regression tests fail |
Date: |
Mon, 22 Feb 2021 09:10:52 -0000 |
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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