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 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.
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).

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

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