Re: [kvm-unit-tests PATCH v4 3/3] s390x/spec_ex: Add test of EXECUTE with odd target address

[Nina Schoetterl-Glausch <nsg@linux.ibm.com>]

On Mon, 2023-04-03 at 17:38 +0200, Thomas Huth wrote:
> On 17/03/2023 14.32, Nina Schoetterl-Glausch wrote:
> > The EXECUTE instruction executes the instruction at the given target
> > address. This address must be halfword aligned, otherwise a
> > specification exception occurs.
> > Add a test for this.
> > 
> > Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
> > Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> > ---
> >   s390x/spec_ex.c | 25 +++++++++++++++++++++++++
> >   1 file changed, 25 insertions(+)
> > 
> > diff --git a/s390x/spec_ex.c b/s390x/spec_ex.c
> > index ab023347..b4b9095f 100644
> > --- a/s390x/spec_ex.c
> > +++ b/s390x/spec_ex.c
> > @@ -177,6 +177,30 @@ static int short_psw_bit_12_is_0(void)
> >   	return 0;
> >   }
> >   
> > +static int odd_ex_target(void)
> > +{
> > +	uint64_t pre_target_addr;
> > +	int to = 0, from = 0x0dd;
> > +
> > +	asm volatile ( ".pushsection .text.ex_odd\n"
> > +		"	.balign	2\n"
> > +		"pre_odd_ex_target:\n"
> > +		"	. = . + 1\n"
> > +		"	lr	%[to],%[from]\n"
> > +		"	.popsection\n"
> > +
> > +		"	larl	%[pre_target_addr],pre_odd_ex_target\n"
> > +		"	ex	0,1(%[pre_target_addr])\n"
> > +		: [pre_target_addr] "=&a" (pre_target_addr),
> > +		  [to] "+d" (to)
> > +		: [from] "d" (from)
> > +	);
> > +
> > +	assert((pre_target_addr + 1) & 1);
> > +	report(to != from, "did not perform ex with odd target");
> > +	return 0;
> > +}
> 
>   Hi Nina,
> 
> FWIW, this fails to compile with Clang v15 here:
> 
> s390x/spec_ex.c:187:4: error: symbol 'pre_odd_ex_target' is already defined
>                  "pre_odd_ex_target:\n"
>                   ^
> <inline asm>:3:1: note: instantiated into assembly here
> pre_odd_ex_target:
> 
> No clue yet why that happens ... but compiling with Clang seems to be broken 
> on some other spots, too, so this is not really critical right now ;-)

Thanks, I guess it inlines the function and emits the asm twice.
Interestingly clang cannot load the address of the misaligned_code symbol in C code due to alignement,
so I had to work around that, too.

> 
>   Thomas
>