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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.03.2025 16:32, Marek Marczykowski-Górecki wrote:
> On Thu, Mar 20, 2025 at 04:21:18PM +0100, Jan Beulich wrote:
>> 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?
> 
> It makes paths in debug symbols relative to xen/ subdir, not the
> repository root. I'm not sure if that is a problem, but it may be for
> some tools.

Yet especially in the symbol table (and hence in strack traces) that's
unnecessary extra space it takes up.

>>> 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.
> 
> Yes, without any of those options, both xen-syms and xen.efi contain
> full source path.

Even in builds without debug info? Imo a goal ought to be to specify the
weakest possible of these options for any particular build mode. I.e.
possibly -ffile-prefix-map= for out of tree builds, else
-fdebug-prefix-map= when DEBUG_INFO=y, else nothing (if possible).

Jan