Re: [PATCH RFC] EFI: strip xen.efi when putting it on the EFI partition

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Jan,

> On 25 Apr 2022, at 11:46, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> 
> With debug info retained, xen.efi can be quite large. Unlike for xen.gz
> there's no intermediate step (mkelf32 there) involved which would strip
> debug info kind of as a side effect. While the installing of xen.efi on
> the EFI partition is an optional step (intended to be a courtesy to the
> developer), adjust it also for the purpose of documenting what distros
> would be expected to do during boot loader configuration (which is what
> would normally put xen.efi into the EFI partition).
> 
> Model the control over stripping after Linux'es module installation,
> except that the stripped executable is constructed in the build area
> instead of in the destination location. This is to conserve on space
> used there - EFI partitions tend to be only a few hundred Mb in size.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> RFC: GNU strip 2.38 appears to have issues when acting on a PE binary:
>     - the new file positions of the sections do not respect the file
>       alignment specified by the header (a resulting looks to work on
>       one EFI implementation where I did actually try it, but I don't
>       think we can rely on that),
>     - file name symbols are also stripped; while there is a separate
>       --keep-file-symbols option (which I would have thought to be on
>       by default anyway), its use makes no difference.
>     Older GNU strip (observed with 2.35.1) doesn't work at all ("Data
>     Directory size (1c) exceeds space left in section (8)").
> 
> --- a/xen/Makefile
> +++ b/xen/Makefile
> @@ -461,6 +461,22 @@ endif
> .PHONY: _build
> _build: $(TARGET)$(CONFIG_XEN_INSTALL_SUFFIX)
> 
> +# Strip
> +#
> +# INSTALL_EFI_STRIP, if defined, will cause xen.efi to be stripped before it
> +# is installed. If INSTALL_EFI_STRIP is '1', then the default option
> +# --strip-debug will be used. Otherwise, INSTALL_EFI_STRIP value will be used
> +# as the option(s) to the strip command.
> +ifdef INSTALL_EFI_STRIP
> +
> +ifeq ($(INSTALL_EFI_STRIP),1)
> +efi-strip-opt := --strip-debug
> +else
> +efi-strip-opt := $(INSTALL_EFI_STRIP)
> +endif
> +
> +endif

This does sound very complex and using combination of ifdef and ifeq on an 
external variable is not done anywhere else.

How about splitting into a variable to turn strip on or off and let the user 
override a local variable setting up the strip options if he wants to ?

Something like:

EFI_STRIP_OPTION ?= "—strip-debug"

And then just using INSTALL_EFI_STRIP to strip or not during the _install phase 

One wanting to use no specific option would have to pass INSTALL_EFI_STRIP=1 
EFI_STRIP_OPTION=“” for example.

Cheers
Bertrand

> +
> .PHONY: _install
> _install: D=$(DESTDIR)
> _install: T=$(notdir $(TARGET))
> @@ -485,6 +501,9 @@ _install: $(TARGET)$(CONFIG_XEN_INSTALL_
>               ln -sf $(T)-$(XEN_FULLVERSION).efi 
> $(D)$(EFI_DIR)/$(T)-$(XEN_VERSION).efi; \
>               ln -sf $(T)-$(XEN_FULLVERSION).efi $(D)$(EFI_DIR)/$(T).efi; \
>               if [ -n '$(EFI_MOUNTPOINT)' -a -n '$(EFI_VENDOR)' ]; then \
> +                     $(if $(efi-strip-opt), \
> +                          $(STRIP) $(efi-strip-opt) -p -o 
> $(TARGET).efi.stripped $(TARGET).efi && \
> +                          $(INSTALL_DATA) $(TARGET).efi.stripped 
> $(D)$(EFI_MOUNTPOINT)/efi/$(EFI_VENDOR)/$(T)-$(XEN_FULLVERSION).efi ||) \
>                       $(INSTALL_DATA) $(TARGET).efi 
> $(D)$(EFI_MOUNTPOINT)/efi/$(EFI_VENDOR)/$(T)-$(XEN_FULLVERSION).efi; \
>               elif [ "$(D)" = "$(patsubst $(shell cd $(XEN_ROOT) && 
> pwd)/%,%,$(D))" ]; then \
>                       echo 'EFI installation only partially done (EFI_VENDOR 
> not set)' >&2; \
> 
>