Re: [PATCH v1 2/2] Strip build path directories in tools, xen and xen/arch/x86

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.03.2025 16:17, Marek Marczykowski-Górecki wrote:
> On Thu, Mar 20, 2025 at 02:35:59PM +0000, Anthony PERARD wrote:
>> On Thu, Mar 20, 2025 at 02:59:04PM +0100, Marek Marczykowski-Górecki wrote:
>>> On Thu, Mar 20, 2025 at 02:49:27PM +0100, Jan Beulich wrote:
>>>> On 20.03.2025 13:51, Marek Marczykowski-Górecki wrote:
>>>>> On Thu, Mar 20, 2025 at 10:18:28AM +0000, Anthony PERARD wrote:
>>>>>> On Wed, Mar 19, 2025 at 02:40:33PM +0100, Marek Marczykowski-Górecki 
>>>>>> wrote:
>>>>>>> There are clearly some build path embedding left. And
>>>>>>> -ffile-prefix-map=/-fdebug-prefix-map= doesn't work correctly with
>>>>>>> XEN_ROOT having xen/.. at the end.
>>>>>>> BTW, would it be acceptable to have this?
>>>>>>>
>>>>>>>     $(call cc-option-add,CFLAGS,CC,-fdebug-prefix-map=$(realpath 
>>>>>>> $(XEN_ROOT))=.)
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Could you avoid using $(XEN_ROOT) in hypervisor build system? (It's fine
>>>>>> in "tools/"). In "xen/", there's a few variables you can use if they are
>>>>>> needed: $(abs_objtree) $(abs_srctree) for absolutes path, and $(srctree)
>>>>>> $(objtree) for relative path. That also should avoid the need to use
>>>>>> $(realpath ).
>>>>>
>>>>> XEN_ROOT is literally "$(abs_srctree)/..". And I need to resolve it to
>>>>> not have /.. for prefix-map to work correctly. Would it be better to use
>>>>> literal $(realpath $(abs_srctree)/..)? Or use just $(abs_srctree) and
>>>>> have paths in debug symbols relative to hypervisor source dir, instead
>>>>> of xen repo root? I'm not sure if that wouldn't confuse some tools...
>>>>
>>>> abs_srctree being computed using realpath, can't we replace
>>>>
>>>> export XEN_ROOT := $(abs_srctree)/..
>>>>
>>>> by something as simpl{e,istic} as
>>>>
>>>> export XEN_ROOT := $(patsubst %/xen,%,$(abs_srctree))
>>>>
>>>> ?
>>>
>>> That works too. It's slightly less robust, but I don't expect "xen"
>>> directory to be renamed, so shouldn't be an issue. I'll leave also a
>>> comment there why not /.. .
>>
>> I don't think $(XEN_ROOT) is present in the binaries produce by the
>> hypervisor's build system. There's only a few use if that variable: to
>> load some makefile, to execute makefile that build xsm policy and to
>> generate cpuid-autogen.h. Otherwise I don't think the compile have this
>> path in the command line. What is going to be in the binary is
>> $(abs_srctree), which you can replace by "./xen" if you want; which mean
>> it doesn't matter if the directory is renamed or not. You might want to
>> also take care of $(abs_objtree) which seems to also be in `xen-syms`
>> when doing out-of-tree build.
> 
> So, you suggest to do -fdebug-prefix-map=$(abs_srctree)=./xen ? That
> appears to work for in-tree builds too.

And why ./xen (question to Anthony)? Just . is quite fine, isn't it?

> But now I actually tested how it looks with out-of-tree builds, and
> indeed $(abs_objtree) is embedded there too. Adding
> -fdebug-prefix-map=$(abs_objtree)=./xen appears to help for this. But,
> -fdebug-prefix-map doesn't help with abs_srctree in out-of-tree builds
> for some reason. -ffile-prefix-map does. And so does -fdebug-prefix-map
> + -fmacro-prefix-map. Is there any preference which one to use? It
> appears as -fmacro-prefix-map and -ffile-prefix-map have the same
> availability in both GCC (8) and Clang (10).

Then the simpler -ffile-prefix-map is better, imo. Question then is
whether any of the options is actually needed at all for in-tree builds.

Jan