[PATCH] msvcrt: Make strlwr/strupr write to the string only if necessary.

[Ambrož Bizjak]

Hi,

This patch fixes a crash in IL-2 Sturmovik: Battle of Stanlingrad
(with some other tweaks the game runs well). Without this, the game
crashes when starting a mission:

Unhandled exception: page fault on write access to 0x1408b81bc in
64-bit code (0x00007f783f3ad8e4).
...
Backtrace:
=>0 0x00007f783f3ad8e4 MSVCRT__strlwr_s_l+0x64() in ucrtbase
(0x000000004a77ccf0)
  1 0x00007f783f3ad96f MSVCRT__strlwr+0x1e(str="idle")
[Z:\build\wine-4.16\dlls\ucrtbase..\msvcrt\string.c:111] in ucrtbase
(0x000000004a77cd30)
  2 0x000000014045a782 EntryPoint+0xffbf1fd1() in il-2 (0x000000004a77cee0)
0x00007f783f3ad8e4 MSVCRT__strlwr_s_l+0x64 in ucrtbase: movb
%al,0xffffffffffffffff(%rbx)

Based on this backtrace, my hypothesis was that the game is calling
strlwr on a read-only string that is already lower-case. I have then
changed strlwr to not assign characters to the string when the value
is unchanged, which fixed the crash. To me this is sufficient evidence
to confirm the hypothesis.

[Marvin]

Hi,

While running your changed tests, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?

Full results can be found at:
https://testbot.winehq.org/JobDetails.pl?Key=60973

Your paranoid android.

=== wxppro (32 bit report) ===

msvcrt:
09dc:string: unhandled exception c0000005 at 77C4675F

=== w2003std (32 bit report) ===

msvcrt:
01e8:string: unhandled exception c0000005 at 77BD75CF

=== wvistau64 (32 bit report) ===

msvcrt:
02d8:string: unhandled exception c0000005 at 7655C22D

=== w2008s64 (32 bit report) ===

msvcrt:
05bc:string: unhandled exception c0000005 at 74CAC22D

=== w7u (32 bit report) ===

msvcrt:
0d50:string: unhandled exception c0000005 at 7618F5A3

=== w8 (32 bit report) ===

msvcrt:
0e8c:string: unhandled exception c0000005 at 7784E2EE

=== w8adm (32 bit report) ===

msvcrt:
0cd8:string: unhandled exception c0000005 at 7558E2EE

=== w864 (32 bit report) ===

msvcrt:
07dc:string: unhandled exception c0000005 at 7745E2EE

=== w1064v1507 (32 bit report) ===

msvcrt:
0780:string: unhandled exception c0000005 at 74268F3E

=== w1064v1809 (32 bit report) ===

msvcrt:
194c:string: unhandled exception c0000005 at 767BABAE

=== w1064v1809_2scr (32 bit report) ===

msvcrt:
1a48:string: unhandled exception c0000005 at 76D7ABAE

=== w1064v1809_ar (32 bit report) ===

msvcrt:
181c:string: unhandled exception c0000005 at 75D9ABAE

=== w1064v1809_he (32 bit report) ===

msvcrt:
0ffc:string: unhandled exception c0000005 at 7581ABAE

=== w1064v1809_ja (32 bit report) ===

msvcrt:
0d84:string: unhandled exception c0000005 at 75DCABAE

=== w1064v1809_zh_CN (32 bit report) ===

msvcrt:
1900:string: unhandled exception c0000005 at 773CABAE

=== wvistau64 (64 bit report) ===

msvcrt:
02d8:string: unhandled exception c0000005 at 000007FEFF413A67

=== w2008s64 (64 bit report) ===

msvcrt:
0390:string: unhandled exception c0000005 at 000007FEFDED3A67

=== w864 (64 bit report) ===

msvcrt:
045c:string: unhandled exception c0000005 at 00007FF9E4D5582E

=== w1064v1507 (64 bit report) ===

msvcrt:
0c98:string: unhandled exception c0000005 at 00007FF8C983C5DA

=== w1064v1809 (64 bit report) ===

msvcrt:
1930:string: unhandled exception c0000005 at 00007FF871DED60A

[Piotr Caban]

Hi Ambrož,

As you have probably seen, the tests are crashing on Windows. If you 
need any hints - the function behaves in the way you have implemented 
only in C locale.

Thanks,
Piotr