linux-kernel - Regression in 2.6.36 in single stepping over hardware breakpoint (Wine)

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Date:	Thu, 28 Oct 2010 02:12:13 +0200
From:	Michael Stefaniuc <mstefani@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Alexandre Julliard <julliard@...ehq.org>
Subject: Regression in 2.6.36 in single stepping over hardware breakpoint
 (Wine)

Hello Frederic,

there is a regression between 2.6.35 and 2.6.36 for 32bit Wine in the 
Wine test checking the single stepping over hardware breakpoints:
/home/michi/work/wine/tools/runtest -q -P wine -M ntdll.dll -T ../../.. 
-p ntdll_test.exe.so /home/michi/work/wine/dlls/ntdll/tests/exception.c 
&& touch exception.ok
exception.c:585: Test failed: eip is wrong: 340002 instead of 340001
exception.c:587: Test failed: B0 flag is not set in Dr6
exception.c:588: Test failed: BS flag is set in Dr6
exception.c:593: Test failed: eip is wrong: 7ed569d3 instead of 340002
make: *** [exception.ok] Error 4

All those tests are in bpx_handler()
http://source.winehq.org/git/wine.git/?a=blob;f=dlls/ntdll/tests/exception.c;h=701b6bba091dddce724075dc41dd2ab407f28ac4;hb=HEAD#l559

A regression test gives:
0c4519e825c9e2b6a8310deff8582f8c35bfbba9 is the first bad commit
commit 0c4519e825c9e2b6a8310deff8582f8c35bfbba9
Author: Frederic Weisbecker <fweisbec@...il.com>
Date:   Thu Jun 24 21:21:27 2010 +0200

     x86: Set resume bit before returning from breakpoint exception

     Instruction breakpoints trigger before the instruction executes,
     and returning back from the breakpoint handler brings us again
     to the instruction that breakpointed. This naturally bring to
     a breakpoint recursion.

     To solve this, x86 has the Resume Bit trick. When the cpu flags
     have the RF flag set, the next instruction won't trigger any
     instruction breakpoint, and once this instruction is executed,
     RF is cleared back.

     This let's us jump back to the instruction that triggered the
     breakpoint without recursion.

     Use this when an instruction breakpoint triggers.

     Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
     Cc: Will Deacon <will.deacon@....com>
     Cc: Prasad <prasad@...ux.vnet.ibm.com>
     Cc: Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>
     Cc: Paul Mackerras <paulus@...ba.org>
     Cc: Ingo Molnar <mingo@...e.hu>
     Cc: Jason Wessel <jason.wessel@...driver.com>

:040000 040000 2eae1fa5f90b141d60fe28a971a618e9c0b1a232 
e27fd94a1beb10e3688d555bd74c888b6a310293 M      arch

Reverting this patch on top of 2.6.36 makes the problem go away.

The problem is 100% reproducible and I see it in 32bit Wine on both
32bit and 64bit Linux. The regression might affect also 64bit Wine but
those exception tests aren't compiled for 64bit Wine due to the lack of
compiler support for win64 exceptions; so we cannot test it.


Steps to reproduce:
-------------------
Any Wine version wine-1.2 or newer will do (either a tarball from
http://sourceforge.net/projects/wine/files/Source/ or from git
    git clone git://source.winehq.org/git/wine.git
./configure
make
cd dlls/ntdll/tests/
make exception.ok

Test results: The above errors on lines 585, 587, 588, 593 should not show
up. Additionally there should be no error in line 665 as that means the 
tests
didn't run (there was a temporary regression in the 2.6.36-rc phase that
produced the test failed on line 665; the patch from commit 89e45aac42d4
was needed at each bisection point).


For 32bit Wine builds on a x86_64 machine a pretty complete 32bit setup
is needed too, but configure will let one know. If configure doesn't
errors out but produces warnings, those can be safely ignored. It means
the dependencies are optional and those aren't needed to reproduce this
bug.  http://wiki.winehq.org/WineOn64bit has a lot more info on setting
this up.

bye
         michael
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