For (aiui) backwards compatibility reasons, gcc defaults to a mode that was the exclusive one up to gcc4.8, establishing 32-byte alignment for aggregates larger than a certain size. We don't rely on such, and hence we can do with the psABI-compliant 16-byte alignment.
Savings in the build I'm looking at: - .data.ro_after_init 344 bytes - .rodata + .data.rel.ro 1904 bytes - .init.*data.cf_clobber 232 bytes - .init (overall) 688 bytes - .data.read_mostly 864 bytes - .data 600 bytes - .bss 1472 bytes Overall xen-syms' _end happens to move down there by 2 pages. Clang doesn't support the option, presumably because they never over- aligned data. Signed-off-by: Jan Beulich <jbeul...@suse.com> --- a/xen/arch/x86/arch.mk +++ b/xen/arch/x86/arch.mk @@ -8,6 +8,9 @@ CFLAGS += -DXEN_IMG_OFFSET=$(XEN_IMG_OFF # Prevent floating-point variables from creeping into Xen. CFLAGS += -msoft-float +# Don't needlessly over-align larger aggregates. +CFLAGS-$(CONFIG_CC_IS_GCC) += -malign-data=abi + $(call cc-options-add,CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS)) $(call cc-option-add,CFLAGS,CC,-Wnested-externs) $(call as-option-add,CFLAGS,CC,".equ \"x\"$(comma)1",-DHAVE_AS_QUOTED_SYM)
