[Bug 60123] New: OutputDebugStringA/W payloads truncated at ~300 bytes in +debugstr/+seh channel output

[WineHQ Bugzilla]

http://bugs.winehq.org/show_bug.cgi?id=60123

            Bug ID: 60123
           Summary: OutputDebugStringA/W payloads truncated at ~300 bytes
                    in +debugstr/+seh channel output
           Product: Wine
           Version: 11.14
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: ntdll
          Assignee: [e-mail]
          Reporter: [e-mail]
  Target Milestone: ---
      Distribution: ---

Applications that emit long strings via OutputDebugStringA/W have their
payloads truncated in wine's debug channel output. Both WINEDEBUG=+debugstr
(warn:debugstr:OutputDebugStringA "...") and WINEDEBUG=+seh
(warn:seh:dispatch_exception "...") print at most ~300 bytes followed by
`"...`, because wine_dbgstr_an/wine_dbgstr_wn (include/wine/debug.h) format
into a fixed `char buffer[300]`.

To Reproduce: call OutputDebugStringA with a 400-char string and run with
WINEDEBUG=+debugstr. Output ends with `"...` after ~300 chars.

1. Compile this test program with mingw:

```
   #include <windows.h>
   int main(void) {
       char buf[500];
       for (int i = 0; i < 400; i++) buf[i] = 'A' + (i % 26);
       buf[400] = 0;
       OutputDebugStringA(buf);
       OutputDebugStringA("short line\r\n");
       return 0;
   }
```

```
   $ x86_64-w64-mingw32-gcc dbg.c -o dbg.exe
```

2. Run under wine with the debugstr channel:

```
   $ WINEDEBUG=+debugstr wine ./dbg.exe
```

Actual output (400-char payload clipped at ~300, note the trailing `"...`):

```
   0024:warn:debugstr:OutputDebugStringA
"ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDE"...
   0024:warn:debugstr:OutputDebugStringA "short line\r\n"
```

Expected: the full 400-character string, as a debugger or DBWIN listener
would receive on Windows.

Same truncation occurs with WINEDEBUG=+seh (warn:seh:dispatch_exception).

Side note on Windows behaviour: On Windows the full string is always delivered
to consumers. A debugger attached via WaitForDebugEvent receives
`OUTPUT_DEBUG_STRING_INFO` with the complete length (read via
`ReadProcessMemory`), and `DBWIN_BUFFER` listeners (e.g. Sysinternals
DebugView) receive up to 4 KiB per frame, with longer strings split across
frames rather than dropped.

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