Re: [kvm-unit-tests GIT PULL v2 11/14] s390x: Add tests for execute-type instructions

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

On Tue, 2023-04-04 at 16:15 +0200, Thomas Huth wrote:
> On 04/04/2023 13.36, Nico Boehr wrote:
> > From: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> > 
> > Test the instruction address used by targets of an execute instruction.
> > When the target instruction calculates a relative address, the result is
> > relative to the target instruction, not the execute instruction.
> > 
> > Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
> > Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> > Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> > Link: https://lore.kernel.org/r/20230317112339.774659-1-nsg@linux.ibm.com
> > Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
> > ---
> >   s390x/Makefile      |   1 +
> >   s390x/ex.c          | 188 ++++++++++++++++++++++++++++++++++++++++++++
> >   s390x/unittests.cfg |   3 +
> >   .gitlab-ci.yml      |   1 +
> >   4 files changed, 193 insertions(+)
> >   create mode 100644 s390x/ex.c
> > 
> > diff --git a/s390x/Makefile b/s390x/Makefile
> > index ab146eb..a80db53 100644
> > --- a/s390x/Makefile
> > +++ b/s390x/Makefile
> > @@ -39,6 +39,7 @@ tests += $(TEST_DIR)/panic-loop-extint.elf
> >   tests += $(TEST_DIR)/panic-loop-pgm.elf
> >   tests += $(TEST_DIR)/migration-sck.elf
> >   tests += $(TEST_DIR)/exittime.elf
> > +tests += $(TEST_DIR)/ex.elf
> >   
> >   pv-tests += $(TEST_DIR)/pv-diags.elf
> >   
> > diff --git a/s390x/ex.c b/s390x/ex.c
> > new file mode 100644
> > index 0000000..dbd8030
> > --- /dev/null
> > +++ b/s390x/ex.c
> > @@ -0,0 +1,188 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Copyright IBM Corp. 2023
> > + *
> > + * Test EXECUTE (RELATIVE LONG).
> > + * These instructions execute a target instruction. The target instruction is formed
> > + * by reading an instruction from memory and optionally modifying some of its bits.
> > + * The execution of the target instruction is the same as if it was executed
> > + * normally as part of the instruction sequence, except for the instruction
> > + * address and the instruction-length code.
> > + */
> > +
> > +#include <libcflat.h>
> > +
> > +/*
> > + * Accesses to the operand of execute-type instructions are instruction fetches.
> > + * Minimum alignment is two, since the relative offset is specified by number of halfwords.
> > + */
> > +asm (  ".pushsection .text.exrl_targets,\"x\"\n"
> > +"	.balign	2\n"
> > +"	.popsection\n"
> > +);
> > +
> > +/*
> > + * BRANCH AND SAVE, register register variant.
> > + * Saves the next instruction address (address from PSW + length of instruction)
> > + * to the first register. No branch is taken in this test, because 0 is
> > + * specified as target.
> > + * BASR does *not* perform a relative address calculation with an intermediate.
> > + */
> > +static void test_basr(void)
> > +{
> > +	uint64_t ret_addr, after_ex;
> > +
> > +	report_prefix_push("BASR");
> > +	asm volatile ( ".pushsection .text.exrl_targets\n"
> > +		"0:	basr	%[ret_addr],0\n"
> > +		"	.popsection\n"
> > +
> > +		"	larl	%[after_ex],1f\n"
> > +		"	exrl	0,0b\n"
> > +		"1:\n"
> > +		: [ret_addr] "=d" (ret_addr),
> > +		  [after_ex] "=d" (after_ex)
> > +	);
> > +
> > +	report(ret_addr == after_ex, "return address after EX");
> > +	report_prefix_pop();
> > +}
> > +
> > +/*
> > + * BRANCH RELATIVE AND SAVE.
> > + * According to PoP (Branch-Address Generation), the address calculated relative
> > + * to the instruction address is relative to BRAS when it is the target of an
> > + * execute-type instruction, not relative to the execute-type instruction.
> > + */
> > +static void test_bras(void)
> > +{
> > +	uint64_t after_target, ret_addr, after_ex, branch_addr;
> > +
> > +	report_prefix_push("BRAS");
> > +	asm volatile ( ".pushsection .text.exrl_targets\n"
> > +		"0:	bras	%[ret_addr],1f\n"
> > +		"	nopr	%%r7\n"
> > +		"1:	larl	%[branch_addr],0\n"
> > +		"	j	4f\n"
> > +		"	.popsection\n"
> > +
> > +		"	larl	%[after_target],1b\n"
> > +		"	larl	%[after_ex],3f\n"
> > +		"2:	exrl	0,0b\n"
> > +/*
> > + * In case the address calculation is correct, we jump by the relative offset 1b-0b from 0b to 1b.
> > + * In case the address calculation is relative to the exrl (i.e. a test failure),
> > + * put a valid instruction at the same relative offset from the exrl, so the test continues in a
> > + * controlled manner.
> > + */
> > +		"3:	larl	%[branch_addr],0\n"
> > +		"4:\n"
> > +
> > +		"	.if (1b - 0b) != (3b - 2b)\n"
> > +		"	.error	\"right and wrong target must have same offset\"\n"
> > +		"	.endif\n"
> 
> FWIW, this is failing with Clang 15 for me:
> 
> s390x/ex.c:81:4: error: expected absolute expression
>                  "       .if (1b - 0b) != (3b - 2b)\n"
>                   ^
> <inline asm>:12:6: note: instantiated into assembly here
>          .if (1b - 0b) != (3b - 2b)

Seems gcc is smarter here than clang.

>              ^
> s390x/ex.c:82:4: error: right and wrong target must have same offset
>                  "       .error  \"right and wrong target must have same 
> offset\"\n"
>                   ^
> <inline asm>:13:2: note: instantiated into assembly here
>          .error  "right and wrong target must have same offset"
>          ^
> 2 errors generated.
> 
> Any easy ways to fix this?

Just deleting that .if block would work, it's basically only a static assert.
What do you think?
Other than that I can't think of anything.

> 
>   Thomas
>