Re: [PATCH v2 3/4] Add DWARF index cache

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2018-07-27 17:24, Eli Zaretskii wrote:
> If we think this details is likely to change, or have other good
> reasons not divulge this, I'm okay with keeping silent about it.  But
> if chances are this will stay forever (or thereabouts), I think the
> details is important enough to tell the users.

If you see a realistic use case where this information would be useful 
to users, I am fine with including it.  But I can't really think of any, 
and mentioning it would more or less paint us into a corner should we 
need to change it.  Cache files are meant to be written and read by GDB, 
not to be interoperable with other programs.

>> >> +      /* If we get EEXIST and the existing path is a directory, then
>> >> we're
>> >> +         happy.  If it exists, but it's a regular file and this is
>> >> not the last
>> >> +         component, we'll fail at the next component.  If this is the
>> >> last
>> >> +         component, the caller will fail with ENOTDIR when trying to
>> >> +         open/create a file under that path.  */
>> >> +      if (mkdir (start, 0700) != 0)
>> >
>> > This will not work on Windows.
>> 
>> Which part of it?
> 
> mkdir accepts only one argument, not 2.

It builds fine with x86_64-w64-mingw32-g++ on Linux here.  It looks like 
gnulib offers a compatibility fix, so I guess it's ok:

https://www.gnu.org/software/gnulib/manual/html_node/mkdir.html

Did you see an actual failure?

>> > Does this mean this feature will only work on systems with mmap?
>> 
>> Indeed.  There is an equivalent API for Windows though I think:
>> 
>> https://docs.microsoft.com/en-us/windows/desktop/Memory/file-mapping
>> 
>> I can't really do the Windows bits, because I just don't have the
>> competence to write software for Windows.  Every time I tried to build
>> GDB for Windows, I failed miserably (do we have a guide for that?).  
>> So
>> my thought (including for the mkdir_recursive function) was that
>> somebody who used Windows could later implement the missing parts.
> 
> Fair enough.
> 
>> Also, I guess that somebody debugging native executables on Windows
>> wouldn't have a use for the cache, because indices only work for DWARF
>> debug info.
> 
> MinGW uses DWARF debug info for quite a few years now, so caching will
> definitely be useful.

Ah, I didn't know that, thanks.  So it produces DWARF embedded in the PE 
executable?  Then yes, it would be useful.

Thanks,

Simon