On Sat, Jan 10, 2015 at 09:14:03PM +0100, Denys Vlasenko wrote:
> From 2f636e0a92db898f2bdb592027aa302fcb32a326 Mon Sep 17 00:00:00 2001
> From: Denys Vlasenko <[email protected]>
> To: [email protected]
> Subject: [PATCH 3/4] x86: open-code register save/restore in trace_hardirqs
> thunks
>
> This is a preparatory patch for change in "struct pt_regs"
> handling in entry_64.S.
>
> trace_hardirqs thunks were (ab)using a part of pt_regs
> handling code, namely SAVE_ARGS/RESTORE_ARGS macros,
> to save/restore registers across C function calls.
>
> Since SAVE_ARGS is going to be changed, open-code
> register saving/restoring here. Take a page from thunk_32.S
> and use push/pop insns instead of movq, they are far shorter:
> 1 or 2 bytes versus 5, and no need for insns to adjust %rsp:
>
> text data bss dec hex filename
> 333 40 0 373 175 thunk_64_movq.o
> 104 40 0 144 90 thunk_64_push_pop.o
>
> Incidentally, this removes a bit of dead code:
> one SAVE_ARGS was used just to emit a CFI annotation,
> but it also generated unreachable assembly insns.
>
> Signed-off-by: Denys Vlasenko <[email protected]>
> CC: Linus Torvalds <[email protected]>
> CC: Oleg Nesterov <[email protected]>
> CC: "H. Peter Anvin" <[email protected]>
> CC: Borislav Petkov <[email protected]>
> CC: Andy Lutomirski <[email protected]>
> CC: Frederic Weisbecker <[email protected]>
> CC: X86 ML <[email protected]>
> CC: Alexei Starovoitov <[email protected]>
> CC: Will Drewry <[email protected]>
> CC: Kees Cook <[email protected]>
> CC: [email protected]
> ---
> arch/x86/lib/thunk_64.S | 46 ++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 42 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/lib/thunk_64.S b/arch/x86/lib/thunk_64.S
> index b30b5eb..8ec443a 100644
> --- a/arch/x86/lib/thunk_64.S
> +++ b/arch/x86/lib/thunk_64.S
> @@ -17,9 +17,27 @@
> CFI_STARTPROC
>
> /* this one pushes 9 elems, the next one would be %rIP */
> - SAVE_ARGS
> + pushq_cfi %rdi
> + CFI_REL_OFFSET rdi, 0
Btw, why the second CFI annotation?
pushq_cfi does already CFI_ADJUST_CFA_OFFSET 8. Can't we use one and
hide it in the macro?
Btw, patch boots fine in the guest.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
