Re: [Xen-devel] [PATCH v2 4/5] alternative/x86/arm32: Align altinstructions (and altinstr_replacement) sections.

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx> 07/26/17 9:50 PM >>>
>On x86 the bloat-o-meter detects that with this change the file shrinks:
>add/remove: 1/0 grow/shrink: 0/2 up/down: 156/-367 (-211)
>function                                     old     new   delta
>get_page_from_gfn                              -     156    +156
>do_mmu_update                               4578    4569      -9
>do_mmuext_op                                5604    5246    -358
>Total: Before=3170439, After=3170228, chg -0.01%

This looks unexpected, and hence I'd like to ask for an explanation. If
anything I'd expect the image size to grow (slightly).

>--- a/xen/include/asm-x86/alternative.h
>+++ b/xen/include/asm-x86/alternative.h
>@@ -56,10 +56,12 @@ extern void alternative_instructions(void);
 >
>#define ALTERNATIVE_N(newinstr, feature, number)       \
>".pushsection .altinstructions,\"a\"\n"                \
>+      ".p2align 2\n"                                  \

Can't this then be accompanied by dropping the (over-)alignment
done in xen.lds.S?

>ALTINSTR_ENTRY(feature, number)                        \
>".section .discard,\"a\",@progbits\n"          \
>DISCARD_ENTRY(number)                          \
>".section .altinstr_replacement, \"ax\"\n"     \
>+      ".p2align 2\n"                                  \

This surely isn't needed on x86.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel