cygport may not create debug info if top directory contains a symlink

[Brian Inglis]

On 2023-09-17 08:01, Jon Turney via Cygwin-apps wrote:
> On 16/09/2023 15:17, Christian Franke via Cygwin wrote:
>> Found during tests of busybox package:
>> If the path of the top build directory contains a symlink and the project's 
>> build scripts normalize pathnames, no debug info is created by cygport.
>>
>> This is because options like
>>   -fdebug-prefix-map=${B}=/usr/src/debug/${PF}
>> have no effect because ${B} contains a symlink but the compiler is run with 
>> the real source path.
> 
> I think that there was some historical bug with gcc where a relative path for 
> the old path in this mapping wasn't correctly handled, which is why were using 
> an absolute path here at all.
> 
> So changing it to something like [1] (if that works), might be better.
> 
> [1] 
> https://github.com/jon-turney/cygport/commit/4175d456a9184c5cdebd8bfb4b5ba30583cedd66
> 
> Sidenote: we should probably also be using file-prefix-map, now we're on a gcc 
> which supports it.
> 
>> The postinstall code then does not find any line number info with source path 
>> /usr/src/debug/${PF}/...
>>
>> Could be fixed easily in line 414 of /bin/cygport:
>>
>> -declare -r top=$(cd ${_topdir}; pwd);
>> +declare -r top=$(cd ${_topdir}; /bin/pwd);
> 
> Can you explain why this makes a difference?

In cygport, pwd is a bash builtin defaulting to -L; /bin/pwd defaults to -P.
Both commands support both options and we might expect the same output.
It would be better to use builtin `pwd -P` if that produces the correct result.
An STC script which creates test dirs to demonstrate the issue and show the 
alternative outputs would be nice so anyone can see.

>> No patch provided because I'm not sure whether this has other negative side 
>> effects.
>>
>> If this is the case, it possibly makes sense to print a warning if "$(pwd)" != 
>> "$(/bin/pwd)".
> 
> This is not unreasonable, and I would take a patch doing this, as there have 
> been places in cygport where there are bugs handling that in the past (and 
> probably still are some, since it's not something that gets tested often).

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry