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

[Jon Turney]

On 30/10/2023 16:37, Christian Franke via Cygwin-apps wrote:
> Jon Turney wrote:
>> On 20/09/2023 11:58, Christian Franke via Cygwin-apps wrote:
>>> Brian Inglis wrote:
>>>> 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?
>>>
>>> I guess the == without ${B} is intentional because it makes the debug 
>>> source path relative to ${B} as lines 535-536 also do.
>>
[...]>
>> (It's unclear to me how gcc compares paths to apply this mapping. If 
>> it's a literal string prefix, rather than on some (semi-)canonicalized 
>> path, then we're maybe going to lose here sometimes, depending on the 
>> vagaries of the build-system, unless we list all of relative, 
>> absolute, and canonical absolute paths?)
>>
>> (But then maybe we can push dealing with or indicating which of those 
>> is correct off onto the individual cygport?)
>>
> 
> Adding this if "$(cd ${S} && pwd -P)" != "${S}" should IMO be safe:
>    -fdebug-prefix-map=$(cd ${B} && pwd -P)=/usr/src/debug/${PF}
>    -fdebug-prefix-map=$(cd ${S} && pwd -P)=/usr/src/debug/${PF}
> (or use realpath)
> 

So it seems there's a new flag '-fcanon-prefix-map' in GCC 13, which 
looks like it maybe solves this problem.