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Re: [Xen-devel] [PATCH RFC for-4.13 09/10] xen/arm: asm: Replace use of ALTERNATIVE with alternative_if

To: Stefano Stabellini <sstabellini@xxxxxxxxxx>

From: Julien Grall <Julien.Grall@xxxxxxx>

Date: Tue, 1 Oct 2019 22:44:04 +0000

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Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, nd <nd@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, "andrii.anisov@xxxxxxxxx" <andrii.anisov@xxxxxxxxx>

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Thread-topic: [PATCH RFC for-4.13 09/10] xen/arm: asm: Replace use of ALTERNATIVE with alternative_if

Hi Stefano, On 01/10/2019 23:19, Stefano Stabellini wrote: > On Thu, 26 Sep 2019, Julien Grall wrote: >> Using alternative_if makes the code a bit more streamlined. >> >> Take the opportunity to use the new auto-nop infrastructure to avoid >> counting the number of nop in the else part for arch/arm/arm64/entry.S >> >> Signed-off-by: Julien Grall <julien.grall@xxxxxxx> >> >> --- >> This is pretty much a matter of taste, but at least for arm64 this >> allows us to use the auto-nop infrastructure. So the arm32 is more >> to keep inline with arm64. >> --- >> xen/arch/arm/arm32/entry.S | 9 ++++++--- >> xen/arch/arm/arm64/entry.S | 8 +++++--- >> 2 files changed, 11 insertions(+), 6 deletions(-) >> >> diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S >> index 0b4cd19abd..1428cd3583 100644 >> --- a/xen/arch/arm/arm32/entry.S >> +++ b/xen/arch/arm/arm32/entry.S >> @@ -65,9 +65,12 @@ save_guest_regs: >> * If the SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT has been set in the >> cpu >> * feature, the checking of pending SErrors will be skipped. >> */ >> - ALTERNATIVE("nop", >> - "b skip_check", >> - SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT) >> + alternative_if SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT >> + nop >> + alternative_else >> + b skip_check >> + alternative_endif > > This could be written as: > > alternative_if_not SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT > b skip_check > alternative_else_nop_endif Actually my implementation is wrong :/. We want to skip the check if the cap is set. So this should be: alternative_if SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT b skip_check alternative_else_nop_endif > > >> /* >> * Start to check pending virtual abort in the gap of Guest -> HYP >> * world switch. >> diff --git a/xen/arch/arm/arm64/entry.S b/xen/arch/arm/arm64/entry.S >> index 458d12f188..91cf6ee6f4 100644 >> --- a/xen/arch/arm/arm64/entry.S >> +++ b/xen/arch/arm/arm64/entry.S >> @@ -170,9 +170,11 @@ >> * is not set. If a vSError took place, the initial exception will >> be >> * skipped. Exit ASAP >> */ >> - ALTERNATIVE("bl check_pending_vserror; cbnz x0, 1f", >> - "nop; nop", >> - SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT) >> + alternative_if SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT This would need to be alternative_if_not as want to call the function when the cap is not set. >> + bl check_pending_vserror >> + cbnz x0, 1f >> + alternative_else_nop_endif >> + >> mov x0, sp >> bl enter_hypervisor_from_guest_noirq >> msr daifclr, \iflags >> -- >> 2.11.0 >> Cheeers, -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel

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