[PATCH 1/3] makedep: Align PE sections so they can be mmapped.

Rémi Bernon rbernon at codeweavers.com
Wed May 27 06:49:21 CDT 2020

On 5/25/20 5:26 PM, Jacek Caban wrote:
> On 25.05.2020 16:32, Rémi Bernon wrote:
>> I could also see that some CROSSDEBUG checks look for "split" prefix in
>> makedep, and some other set the variable to dwarf. It's not clear to me
>> what this variable is supposed to be set to (other than "pdb"). Does
>> "dwarf" mean separate file as well?
> No, "dwarf" means that debug info will be embedded in module PE files, 
> which has always been the default. "dwarf" part of "split-dwarf" is 
> important for configure script to apply dwarf-specific flags. "dwarf," 
> "split-dwarf" and "pdb" are the only configs for which I know a real 
> use, but in theory you could set it to anything else as long as you take 
> care of CROSSCFLAGS yourself. "stabs" and "split-stabs" should be in 
> theory achievable this way (but I didn't try).
> Jacek

Alright. So, "split*" means that the debug sections are extracted to a 
separate file, and, currently, this file is also a PE file, as the 
default objcopy operation is to use the same output format as the source 

Having the debug section in an ELF file instead in this case shouldn't 
be an issue right? Gdb and any other tool that were already able to 
parse DWARF from PE files should be able to parse DWARF from ELF without 
trouble. Using an ELF container allows perf to read it. I don't think 
there's anything that requires PE container with DWARF debug info, but 
maybe there is?

Regarding the default name and location of this ELF module, I see that 
we already implement in dbghelp the same logic as gdb does, which 
includes looking for .debug/debugfile, where debugfile is the contents 
of GNU debuglink, so this should work fine as well, while at the same 
time making perf work OOTB.

 From a quick test, as long as the .debug folder is also copied 
alongside the dll in the prefix, both winedbg and winedbg --gdb are 
happy with the ELF container.

So, in the end, although I understand the root issue is some limitation 
of perf itself, this feels much simpler to fix in Wine with these small 
tweaks that makes every tool happy, than to try implementing PE support 
in perf. I think it would require much more work there, and would be way 
harder to justify if it were to be upstreamed (this is clearly a Wine 
specific use-case and I'm not sure how eager perf maintainers would be 
to have huge code changes just for the sake of PE module parsing).
Rémi Bernon <rbernon at codeweavers.com>

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