Commit b7b205c3 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Peter Zijlstra
Browse files

x86/xen: Move hypercall_page to top of the file 



Because hypercall_page is page-aligned, the assembler inexplicably adds
an unreachable jump from after the end of the previous code to the
beginning of hypercall_page.

That confuses objtool, understandably.  It also creates significant text
fragmentation.  As a result, much of the object file is wasted text
(nops).

Move hypercall_page to the beginning of the file to both prevent the
text fragmentation and avoid the dead jump instruction.

$ size /tmp/head_64.before.o /tmp/head_64.after.o
   text	   data	    bss	    dec	    hex	filename
  10924	 307252	   4096	 322272	  4eae0	/tmp/head_64.before.o
   6823	 307252	   4096	 318171	  4dadb	/tmp/head_64.after.o

Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Link: https://lkml.kernel.org/r/20210820193107.omvshmsqbpxufzkc@treble
parent 9af9dcf1

arch/x86/xen/xen-head.S

+17 −17
Original line number Diff line number Diff line
@@ -20,6 +20,23 @@ 
#include <xen/interface/xen-mca.h>

#include <asm/xen/interface.h>



.pushsection .text

	.balign PAGE_SIZE

SYM_CODE_START(hypercall_page)

	.rept (PAGE_SIZE / 32)

		UNWIND_HINT_FUNC

		.skip 31, 0x90

		ret

	.endr



#define HYPERCALL(n) \

	.equ xen_hypercall_##n, hypercall_page + __HYPERVISOR_##n * 32; \

	.type xen_hypercall_##n, @function; .size xen_hypercall_##n, 32

#include <asm/xen-hypercalls.h>

#undef HYPERCALL

SYM_CODE_END(hypercall_page)

.popsection



#ifdef CONFIG_XEN_PV

	__INIT

SYM_CODE_START(startup_xen)
@@ -64,23 +81,6 @@ SYM_CODE_END(asm_cpu_bringup_and_idle) 
#endif

#endif



.pushsection .text

	.balign PAGE_SIZE

SYM_CODE_START(hypercall_page)

	.rept (PAGE_SIZE / 32)

		UNWIND_HINT_FUNC

		.skip 31, 0x90

		ret

	.endr



#define HYPERCALL(n) \

	.equ xen_hypercall_##n, hypercall_page + __HYPERVISOR_##n * 32; \

	.type xen_hypercall_##n, @function; .size xen_hypercall_##n, 32

#include <asm/xen-hypercalls.h>

#undef HYPERCALL

SYM_CODE_END(hypercall_page)

.popsection



	ELFNOTE(Xen, XEN_ELFNOTE_GUEST_OS,       .asciz "linux")

	ELFNOTE(Xen, XEN_ELFNOTE_GUEST_VERSION,  .asciz "2.6")

	ELFNOTE(Xen, XEN_ELFNOTE_XEN_VERSION,    .asciz "xen-3.0")