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

[Thomas Huth <thuth@xxxxxxxxxx>]

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@xxxxxxxxxxxxx>
> > > ---
> > >    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@xxxxxxxxxx>
> > >     */
> > >    #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