Re: [kvm-unit-tests PATCH v2 4/8] s390x: Introduce and use CALL_INT_HANDLER macro

From: Thomas Huth <thuth@redhat.com>
To: Janosch Frank <frankja@linux.ibm.com>, kvm@vger.kernel.org
Cc: linux-s390@vger.kernel.org, imbrenda@linux.ibm.com,
	pmorel@linux.ibm.com, david@redhat.com
Subject: Re: [kvm-unit-tests PATCH v2 4/8] s390x: Introduce and use CALL_INT_HANDLER macro
Date: Wed, 17 Feb 2021 16:55:13 +0100	[thread overview]
Message-ID: <313546fb-35df-22ab-79f8-d5b49286058f@redhat.com> (raw)
In-Reply-To: <20210217144116.3368-5-frankja@linux.ibm.com>

On 17/02/2021 15.41, Janosch Frank wrote:
> The ELF ABI dictates that we need to allocate 160 bytes of stack space
> for the C functions we're calling. Since we would need to do that for
> every interruption handler which, combined with the new stack argument
> being saved in GR2, makes cstart64.S look a bit messy.
> 
> So let's introduce the CALL_INT_HANDLER macro that handles all of
> that, calls the C interrupt handler and handles cleanup afterwards.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
>   s390x/cstart64.S | 28 +++++-----------------------
>   s390x/macros.S   | 17 +++++++++++++++++
>   2 files changed, 22 insertions(+), 23 deletions(-)
> 
> diff --git a/s390x/cstart64.S b/s390x/cstart64.S
> index 35d20293..666a9567 100644
> --- a/s390x/cstart64.S
> +++ b/s390x/cstart64.S
> @@ -92,37 +92,19 @@ memsetxc:
>   
>   .section .text
>   pgm_int:
> -	SAVE_REGS_STACK
> -	lgr     %r2, %r15
> -	brasl	%r14, handle_pgm_int
> -	RESTORE_REGS_STACK
> -	lpswe	GEN_LC_PGM_OLD_PSW
> +	CALL_INT_HANDLER handle_pgm_int, GEN_LC_PGM_OLD_PSW
>   
>   ext_int:
> -	SAVE_REGS_STACK
> -	lgr     %r2, %r15
> -	brasl	%r14, handle_ext_int
> -	RESTORE_REGS_STACK
> -	lpswe	GEN_LC_EXT_OLD_PSW
> +	CALL_INT_HANDLER handle_ext_int, GEN_LC_EXT_OLD_PSW
>   
>   mcck_int:
> -	SAVE_REGS_STACK
> -	brasl	%r14, handle_mcck_int
> -	RESTORE_REGS_STACK
> -	lpswe	GEN_LC_MCCK_OLD_PSW
> +	CALL_INT_HANDLER handle_mcck_int, GEN_LC_MCCK_OLD_PSW
>   
>   io_int:
> -	SAVE_REGS_STACK
> -	lgr     %r2, %r15
> -	brasl	%r14, handle_io_int
> -	RESTORE_REGS_STACK
> -	lpswe	GEN_LC_IO_OLD_PSW
> +	CALL_INT_HANDLER handle_io_int, GEN_LC_IO_OLD_PSW
>   
>   svc_int:
> -	SAVE_REGS_STACK
> -	brasl	%r14, handle_svc_int
> -	RESTORE_REGS_STACK
> -	lpswe	GEN_LC_SVC_OLD_PSW
> +	CALL_INT_HANDLER handle_svc_int, GEN_LC_SVC_OLD_PSW
>   
>   	.align	8
>   initial_psw:
> diff --git a/s390x/macros.S b/s390x/macros.S
> index a7d62c6f..212a3823 100644
> --- a/s390x/macros.S
> +++ b/s390x/macros.S
> @@ -11,6 +11,23 @@
>    *  David Hildenbrand <david@redhat.com>
>    */
>   #include <asm/asm-offsets.h>
> +/*
> + * Exception handler macro that saves registers on the stack,
> + * allocates stack space and calls the C handler function. Afterwards
> + * we re-load the registers and load the old PSW.
> + */
> +	.macro CALL_INT_HANDLER c_func, old_psw
> +	SAVE_REGS_STACK
> +	/* Save the stack address in GR2 which is the first function argument */
> +	lgr     %r2, %r15
> +	/* Allocate stack pace for called C function, as specified in s390 ELF ABI */
> +	slgfi   %r15, 160

By the way, don't you have to store a back chain pointer at the bottom of 
that area, too, if you want to use -mbackchoin in the next patch?

  Thomas

> +	brasl	%r14, \c_func
> +	algfi   %r15, 160
> +	RESTORE_REGS_STACK
> +	lpswe	\old_psw
> +	.endm
> +
>   	.macro SAVE_REGS
>   	/* save grs 0-15 */
>   	stmg	%r0, %r15, GEN_LC_SW_INT_GRS
> 