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

[Thomas Huth <thuth@redhat.com>]

On 17/02/2021 17.22, Janosch Frank wrote:
> On 2/17/21 4:55 PM, Thomas Huth wrote:
>> 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?
> 
> Don't I already do that in #2?

You do it in the SAVE_REGS_STACK patch, yes. But not on the bottom of the 
new 160 bytes stack frame that you've added here. But I guess it doesn't 
really matter for your back traces, since you load %r2 with %r15 before 
decrementing the stack by 160, so this new stack frame simply gets ignored 
anyway.

  Thomas