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

[Brian Inglis]

On 2023-09-18 04:41, Christian Franke via Cygwin-apps wrote:
> Brian Inglis wrote:
>> 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

Should bin/cygport.in:534: not have $B between the == as in line 531:

	declare ${flags}+=" -fdebug-prefix-map=${B}=/usr/src/debug/${PF}"
	...
	declare ${flags}+=" -fdebug-prefix-map==/usr/src/debug/${PF}"

or be hoist above the condition if identical, unless that is some undocumented 
default for cwd?

>>> Sidenote: we should probably also be using file-prefix-map, now we're on a 
>>> gcc which supports it.

... also macro-prefix-map, although it looks like changing to -ffile-prefix-map 
is equivalent to -f*-prefix-map which future proofs the options!

>>>> 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.

> It does.

>> An STC script which creates test dirs to demonstrate the issue and show the 
>> alternative outputs would be nice so anyone can see.

> $ ln -s /usr/src /tmp/source
> 
> $ cd /tmp/source
> 
> $ pwd
> /tmp/source
> 
> $ /bin/pwd
> /usr/src
> 
> $ pwd -P
> /usr/src
> 
> $ /bin/pwd -L
> /tmp/source

Thanks, looks good - care to submit a patch, including above suggestions, to 
cover all bases?

-- 
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