On Thu, Jan 08, 2015 at 05:25:14PM +0100, Denys Vlasenko wrote:
> 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.
>
> 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: 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 | 29 ++++++++++++++++++++++++-----
> 1 file changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/lib/thunk_64.S b/arch/x86/lib/thunk_64.S
> index b30b5eb..03a3883 100644
> --- a/arch/x86/lib/thunk_64.S
> +++ b/arch/x86/lib/thunk_64.S
> @@ -16,10 +16,20 @@
> \name:
> CFI_STARTPROC
>
> - /* this one pushes 9 elems, the next one would be %rIP */
> - SAVE_ARGS
> + subq $9*8, %rsp
> + CFI_ADJUST_CFA_OFFSET 9*8
> + movq_cfi r11, 0*8
> + movq_cfi r10, 1*8
> + movq_cfi r9, 2*8
> + movq_cfi r8, 3*8
> + movq_cfi rax, 4*8
> + movq_cfi rcx, 5*8
> + movq_cfi rdx, 6*8
> + movq_cfi rsi, 7*8
> + movq_cfi rdi, 8*8
>
> .if \put_ret_addr_in_rdi
> + /* 9*8(%rsp) is return addr on stack */
> movq_cfi_restore 9*8, rdi
> .endif
>
> @@ -45,11 +55,20 @@
> #endif
> #endif
>
> - /* SAVE_ARGS below is used only for the .cfi directives it contains. */
> CFI_STARTPROC
> - SAVE_ARGS
> + CFI_ADJUST_CFA_OFFSET 9*8
> restore:
> - RESTORE_ARGS
> + movq_cfi_restore 0*8, r11
> + movq_cfi_restore 1*8, r10
> + movq_cfi_restore 2*8, r9
> + movq_cfi_restore 3*8, r8
> + movq_cfi_restore 4*8, rax
> + movq_cfi_restore 5*8, rcx
> + movq_cfi_restore 6*8, rdx
> + movq_cfi_restore 7*8, rsi
> + movq_cfi_restore 8*8, rdi
> + addq 9*8, %rsp
> + CFI_ADJUST_CFA_OFFSET -9*8
The only nitpick I'd have with this is can we keep the register
saving/restoring order in the code the same as in the SAVE_/RESTORE_ARGS
macros?
SAVE_ARGS starts with the highest offset 9*8, rdi and ends at 0*8 and
r11 and RESTORE_ARGS does that in reverse.
Also, can you post the struct pt_regs change too so that we know where
this is going?
Thanks.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
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