[PATCH 2/4] libbacktrace: detect executable path on windows

[Björn Schäpers]

Am 24.01.2023 um 17:52 schrieb Eli Zaretskii:
>> From: Ian Lance Taylor <iant@golang.org>
>> Date: Tue, 24 Jan 2023 06:35:21 -0800
>> Cc: gcc@hazardy.de, gcc-patches@gcc.gnu.org, gcc@gcc.gnu.org
>>
>>>> On Windows it seems that MAX_PATH is not
>>>> a true limit, as an extended length path may be up to 32767 bytes.
>>>
>>> The limit of 32767 characters (not bytes, AFAIK) is only applicable
>>> when using the Unicode (a.k.a. "wide") versions of the Windows Win32
>>> APIs, see
>>>
>>>    https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation
>>>
>>> Since the above code uses GetModuleFileNameA, which is an "ANSI"
>>> single-byte API, it is still subject to the MAX_PATH limitation, and
>>> MAX_PATH is defined as 260 on Windows headers.
>>
>> Thanks.  Should this code be using GetModuleFileNameW?  Or would that
>> mean that the later call to open will fail?
> 
> We'd need to use _wopen or somesuch, and the file name will have to be
> a wchar_t array, not a char array, yes.  So this is not very practical
> when file names need to be passed between functions, unless they are
> converted to UTF-8 (and back again before using them in Windows APIs).
> 
> And note that even then, the 260-byte limit could be lifted only if
> the user has a new enough Windows version _and_ has opted in to the
> long-name feature by turning it on in the Registry.  Otherwise, file
> names used in "wide" APIs can only break the 260-byte limit if they
> use the special format "\\?\D:\foo\bar", which means file names
> specified by user outside of the program or file names that come from
> other programs will need to be reformatted to this special format.
> 
>> 260 bytes does not seem like very much for a path name these days.
> 
> That's true.  But complications with using longer file names are still
> a PITA on Windows, even though they are a step closer to practically
> possible.

That was basically also my reasoning for choosing the A variant instead of W.