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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.04.2022 14:26, Bertrand Marquis wrote:
> 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 

This "just using INSTALL_EFI_STRIP" is what we have with the present
version as well, and I'm not really looking forward to have two
separate variable to act upon. It was for this particular reason that
I took Linux'es module installation process as a "template".

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

This particular example wouldn't strip anything aiui, and hence would
needlessly touch the binary (and perhaps make changes to it just as a
side effect: For example I'm observing the string table growing, which
I have yet to investigate in binutils).

Jan