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

[Janosch Frank <frankja@linux.ibm.com>]

On 2/17/21 6:03 PM, Thomas Huth wrote:
> 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
> 

Right, I'm currently fixing that up for the next version.

diff --git i/s390x/macros.S w/s390x/macros.S
index b4275c77..13cff299 100644
--- i/s390x/macros.S
+++ w/s390x/macros.S
@@ -22,6 +22,11 @@
        lgr     %r2, %r15
        /* Allocate stack space for called C function, as specified in
s390 ELF ABI */
        slgfi   %r15, 160
+       /*
+        * Save the address of the interrupt stack into the back chain
+        * of the called function.
+        */
+       stg     %r2, STACK_FRAME_INT_BACKCHAIN(%r15)
        brasl   %r14, \c_func
        algfi   %r15, 160
        RESTORE_REGS_STACK