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

Thomas Huth
2023-04-04T14:16:50Z

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)
^
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?

Thomas