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

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

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.

> > 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.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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