Re: [PATCH v2] Strip build path directories in tools and hypervisor

[Jan Beulich <jbeulich@suse.com>]

On 04.09.2025 16:27, Marek Marczykowski-Górecki wrote:
> On Thu, Sep 04, 2025 at 02:58:20PM +0200, Jan Beulich wrote:
>> On 04.09.2025 13:41, Marek Marczykowski-Górecki wrote:
>>> Use -fdebug-prefix-map in preference to -ffile-prefix-map, as it's
>>> available in earlier toolchain versions. But use it together with
>>> -fmacro-prefix-map (if available) for hypervisor build, otherwise it
>>> still contains some paths in out-of-tree builds.
>>
>> I consider it wrong not to use -ffile-prefix-map when available. That
>> already covers more than "debug" and "macro", and it may gain further
>> functionality.
> 
> I asked about that on v1 and got ambiguous answer suggesting the opposite:
> https://lore.kernel.org/xen-devel/0370c0eb1fd9ac00acab016792132fa0b943d384.1742317309.git-series.marmarek@invisiblethingslab.com/T/#m74a8883835e30fb74a85b07a7b14507ee52e7c65

Ambiguous answer(s)? There's no reply to that mail of yours, and I don't
see how the conclusion drawn fits my earlier comment. That was more
towards what I did in v1 of my patch - fall back to the more widely
supported option when the less widely available one can't be used.

>>> --- a/tools/Makefile
>>> +++ b/tools/Makefile
>>> @@ -1,4 +1,4 @@
>>> -XEN_ROOT = $(CURDIR)/..
>>> +XEN_ROOT = $(realpath $(CURDIR)/..)
>>>  
>>>  export PKG_CONFIG_DIR = $(CURDIR)/pkg-config
>>>  
>>> diff --git a/tools/Rules.mk b/tools/Rules.mk
>>> index 725c3c32e9a2..428fce094819 100644
>>> --- a/tools/Rules.mk
>>> +++ b/tools/Rules.mk
>>> @@ -166,6 +166,8 @@ endif
>>>  CFLAGS-$(CONFIG_X86_32) += $(call cc-option,$(CC),-mno-tls-direct-seg-refs)
>>>  CFLAGS += $(CFLAGS-y)
>>>  
>>> +$(call cc-option-add,CFLAGS,CC,-fdebug-prefix-map=$(realpath $(XEN_ROOT))=.)
>>
>> Here and below - no need to use cc-option-add for -fdebug-prefix-map,
>> which all permissible compilers support.
> 
> Ok.
> 
>> Further, again as per reply to Andrew on the thread hanging off of my
>> patch - I don't view it as desirable to leave the tools/ prefix in
>> place, or e.g. for libraries, the entire tools/libs/<subdir>/ part.
>> Imo every binary should have only the path (if any) from its own source
>> root left. (And yes, how to deal with e.g. shared include files isn't
>> quite clear to me, yet. Maybe we actually need to pass two options.)
> 
> I don't think it's valid to strip arbitrary prefixes from debug symbols,
> especially in tools. This will break some automated tools that try to match
> coredumps (and similar) to source code and sometimes even debug symbols
> too. But even for manual usage, having to jump between directories (I'm
> not sure if gdb supports multiple source dirs at once?)

Pretty necessarily: When debugging you might easily cross project boundaries.

> just because you
> happen to debug a binary that use more of libraries isn't exactly
> desirable.
> I think the paths in debug symbols and similar should match the layout
> in the source repository, not a subset of it.

Well, okay, we disagree here. To me, xen.git really is an agglomeration of
too many things in a single repo. If things were properly split, you'd end
up with what I'm asking for anyway.

> Theoretically this doesn't apply to the hypervisor yet, as I'm not aware
> of any tool processing xen memory dumps automatically (and those for
> manual usage are quite unstable, to say the least...). But I don't think
> it's an excuse to have incomplete paths in there, just to save few
> bytes?
> The only case where I can see it would make some sense is out of tree
> build, where indeed it's about just the hypervisor, not the toolstack
> (IMO due to the build system limitation, but well...). But at the same
> time, having different path variant depending on it-tree/out-of-tree
> build feels weird.

Which is why I'm arguing for the dropping of the xen/ prefixes, as that's
how things come out in in-tree builds.

Jan