On 22 May 14 16:23, Christopher Covington wrote: > Hi Larry, > > On 05/22/2014 03:27 PM, Larry Bassel wrote: > > To implement the context tracker properly on arm64, > > a function call needs to be made after debugging and > > interrupts are turned on, but before the lr is changed > > to point to ret_to_user(). If the function call > > is made after the lr is changed the function will not > > return to the correct place. > > > > For similar reasons, defer the setting of x0 so that > > it doesn't need to be saved around the function call > > (save far_el1 in x26 temporarily instead). > > > > Signed-off-by: Larry Bassel <larry.bas...@linaro.org> > > --- > > arch/arm64/kernel/entry.S | 24 +++++++++++++++++------- > > 1 file changed, 17 insertions(+), 7 deletions(-) > > > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > > index e8b23a3..20b336e 100644 > > --- a/arch/arm64/kernel/entry.S > > +++ b/arch/arm64/kernel/entry.S > > @@ -354,7 +354,6 @@ el0_sync: > > lsr x24, x25, #ESR_EL1_EC_SHIFT // exception class > > cmp x24, #ESR_EL1_EC_SVC64 // SVC in 64-bit state > > b.eq el0_svc > > - adr lr, ret_to_user > > cmp x24, #ESR_EL1_EC_DABT_EL0 // data abort in EL0 > > b.eq el0_da > > cmp x24, #ESR_EL1_EC_IABT_EL0 // instruction abort in EL0 > > @@ -383,7 +382,6 @@ el0_sync_compat: > > lsr x24, x25, #ESR_EL1_EC_SHIFT // exception class > > cmp x24, #ESR_EL1_EC_SVC32 // SVC in 32-bit state > > b.eq el0_svc_compat > > - adr lr, ret_to_user > > cmp x24, #ESR_EL1_EC_DABT_EL0 // data abort in EL0 > > b.eq el0_da > > cmp x24, #ESR_EL1_EC_IABT_EL0 // instruction abort in EL0 > > @@ -426,22 +424,26 @@ el0_da: > > /* > > * Data abort handling > > */ > > - mrs x0, far_el1 > > - bic x0, x0, #(0xff << 56) > > + mrs x26, far_el1 > > // enable interrupts before calling the main handler > > enable_dbg_and_irq > > + mov x0, x26 > > + bic x0, x0, #(0xff << 56) > > Nit: I believe you can bit clear with x26 as the source register and omit the > move instruction.
Is that really an improvement (assuming it works)? Are we saving any cycles here? If so, does it matter? It is easy to see what the move instruction is doing. > > Regards, > Christopher > > -- > Employee of Qualcomm Innovation Center, Inc. > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > hosted by the Linux Foundation. Larry -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
