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

[Jan Beulich <jbeulich@xxxxxxxx>]

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 := $(INSTALL_EFI_STRIP)
+endif
+
+endif
+
 .PHONY: _install
 _install: D=$(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; \