Re: [kvm-unit-tests PATCH v8 6/6] s390x: SCLP unit test

David Hildenbrand
2020-01-22T10:40:55Z

On 22.01.20 11:39, Thomas Huth wrote:
> On 22/01/2020 11.32, David Hildenbrand wrote:
>> On 22.01.20 11:31, Thomas Huth wrote:
>>> On 22/01/2020 11.22, David Hildenbrand wrote:
>>>> On 22.01.20 11:10, David Hildenbrand wrote:
>>>>> On 20.01.20 19:42, Claudio Imbrenda wrote:
>>>>>> SCLP unit test. Testing the following:
>>>>>>
>>>>>> * Correctly ignoring instruction bits that should be ignored
>>>>>> * Privileged instruction check
>>>>>> * Check for addressing exceptions
>>>>>> * Specification exceptions:
>>>>>> - SCCB size less than 8
>>>>>> - SCCB unaligned
>>>>>> - SCCB overlaps prefix or lowcore
>>>>>> - SCCB address higher than 2GB
>>>>>> * Return codes for
>>>>>> - Invalid command
>>>>>> - SCCB too short (but at least 8)
>>>>>> - SCCB page boundary violation
>>>>>>
>>>>>> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
>>>>>> Reviewed-by: Thomas Huth <thuth@redhat.com>
>>>>>> Acked-by: Janosch Frank <frankja@linux.ibm.com>
>>>>>> ---
>>>>>> s390x/Makefile | 1 +
>>>>>> s390x/sclp.c | 474 ++++++++++++++++++++++++++++++++++++++++++++
>>>>>> s390x/unittests.cfg | 8 +
>>>>>> 3 files changed, 483 insertions(+)
>>>>>> create mode 100644 s390x/sclp.c
>>>>>>
>>>>>> diff --git a/s390x/Makefile b/s390x/Makefile
>>>>>> index 3744372..ddb4b48 100644
>>>>>> --- a/s390x/Makefile
>>>>>> +++ b/s390x/Makefile
>>>>>> @@ -16,6 +16,7 @@ tests += $(TEST_DIR)/diag288.elf
>>>>>> tests += $(TEST_DIR)/stsi.elf
>>>>>> tests += $(TEST_DIR)/skrf.elf
>>>>>> tests += $(TEST_DIR)/smp.elf
>>>>>> +tests += $(TEST_DIR)/sclp.elf
>>>>>> tests_binary = $(patsubst %.elf,%.bin,$(tests))
>>>>>>
>>>>>> all: directories test_cases test_cases_binary
>>>>>> diff --git a/s390x/sclp.c b/s390x/sclp.c
>>>>>> new file mode 100644
>>>>>> index 0000000..215347e
>>>>>> --- /dev/null
>>>>>> +++ b/s390x/sclp.c
>>>>>> @@ -0,0 +1,474 @@
>>>>>> +/*
>>>>>> + * Service Call tests
>>>>>> + *
>>>>>> + * Copyright (c) 2019 IBM Corp
>>>>>> + *
>>>>>> + * Authors:
>>>>>> + * Claudio Imbrenda <imbrenda@linux.ibm.com>
>>>>>> + *
>>>>>> + * This code is free software; you can redistribute it and/or modify it
>>>>>> + * under the terms of the GNU General Public License version 2.
>>>>>> + */
>>>>>> +
>>>>>> +#include <libcflat.h>
>>>>>> +#include <asm/page.h>
>>>>>> +#include <asm/asm-offsets.h>
>>>>>> +#include <asm/interrupt.h>
>>>>>> +#include <sclp.h>
>>>>>> +
>>>>>> +#define PGM_NONE 1
>>>>>> +#define PGM_BIT_SPEC (1ULL << PGM_INT_CODE_SPECIFICATION)
>>>>>> +#define PGM_BIT_ADDR (1ULL << PGM_INT_CODE_ADDRESSING)
>>>>>> +#define PGM_BIT_PRIV (1ULL << PGM_INT_CODE_PRIVILEGED_OPERATION)
>>>>>> +#define MKPTR(x) ((void *)(uint64_t)(x))
>>>>>> +
>>>>>> +#define LC_SIZE (2 * PAGE_SIZE)
>>>>>> +
>>>>>> +static uint8_t pagebuf[LC_SIZE] __attribute__((aligned(LC_SIZE))); /* scratch pages used for some tests */
>>>>>> +static uint8_t prefix_buf[LC_SIZE] __attribute__((aligned(LC_SIZE))); /* temporary lowcore for test_sccb_prefix */
>>>>>> +static uint8_t sccb_template[PAGE_SIZE]; /* SCCB template to be used */
>>>>>> +static uint32_t valid_code; /* valid command code for READ SCP INFO */
>>>>>> +static struct lowcore *lc;
>>>>>> +
>>>>>> +/**
>>>>>> + * Perform one service call, handling exceptions and interrupts.
>>>>>> + */
>>>>>> +static int sclp_service_call_test(unsigned int command, void *sccb)
>>>>>> +{
>>>>>> + int cc;
>>>>>> +
>>>>>> + sclp_mark_busy();
>>>>>> + sclp_setup_int();
>>>>>> + cc = servc(command, __pa(sccb));
>>>>>> + if (lc->pgm_int_code) {
>>>>>> + sclp_handle_ext();
>>>>>> + return 0;
>>>>>> + }
>>>>>> + if (!cc)
>>>>>> + sclp_wait_busy();
>>>>>> + return cc;
>>>>>> +}
>>>>>> +
>>>>>> +/**
>>>>>> + * Perform one test at the given address, optionally using the SCCB template,
>>>>>> + * checking for the expected program interrupts and return codes.
>>>>>> + *
>>>>>> + * The parameter buf_len indicates the number of bytes of the template that
>>>>>> + * should be copied to the test address, and should be 0 when the test
>>>>>> + * address is invalid, in which case nothing is copied.
>>>>>> + *
>>>>>> + * The template is used to simplify tests where the same buffer content is
>>>>>> + * used many times in a row, at different addresses.
>>>>>> + *
>>>>>> + * Returns true in case of success or false in case of failure
>>>>>> + */
>>>>>> +static bool test_one_sccb(uint32_t cmd, uint8_t *addr, uint16_t buf_len, uint64_t exp_pgm, uint16_t exp_rc)
>>>>>> +{
>>>>>> + SCCBHeader *h = (SCCBHeader *)addr;
>>>>>> + int res, pgm;
>>>>>> +
>>>>>> + /* Copy the template to the test address if needed */
>>>>>> + if (buf_len)
>>>>>> + memcpy(addr, sccb_template, buf_len);
>>>>>> + if (exp_pgm != PGM_NONE)
>>>>>> + expect_pgm_int();
>>>>>> + /* perform the actual call */
>>>>>> + res = sclp_service_call_test(cmd, h);
>>>>>> + if (res) {
>>>>>> + report_info("SCLP not ready (command %#x, address %p, cc %d)", cmd, addr, res);
>>>>>> + return false;
>>>>>> + }
>>>>>> + pgm = clear_pgm_int();
>>>>>> + /* Check if the program exception was one of the expected ones */
>>>>>> + if (!((1ULL << pgm) & exp_pgm)) {
>>>>>> + report_info("First failure at addr %p, buf_len %d, cmd %#x, pgm code %d",
>>>>>> + addr, buf_len, cmd, pgm);
>>>>>> + return false;
>>>>>> + }
>>>>>> + /* Check if the response code is the one expected */
>>>>>> + if (exp_rc && exp_rc != h->response_code) {
>>>>>> + report_info("First failure at addr %p, buf_len %d, cmd %#x, resp code %#x",
>>>>>> + addr, buf_len, cmd, h->response_code);
>>>>>> + return false;
>>>>>> + }
>>>>>> + return true;
>>>>>> +}
>>>>>> +
>>>>>> +/**
>>>>>> + * Wrapper for test_one_sccb to be used when the template should not be
>>>>>> + * copied and the memory address should not be touched.
>>>>>> + */
>>>>>> +static bool test_one_ro(uint32_t cmd, uint8_t *addr, uint64_t exp_pgm, uint16_t exp_rc)
>>>>>> +{
>>>>>> + return test_one_sccb(cmd, addr, 0, exp_pgm, exp_rc);
>>>>>> +}
>>>>>> +
>>>>>> +/**
>>>>>> + * Wrapper for test_one_sccb to set up a simple SCCB template.
>>>>>> + *
>>>>>> + * The parameter sccb_len indicates the value that will be saved in the SCCB
>>>>>> + * length field of the SCCB, buf_len indicates the number of bytes of
>>>>>> + * template that need to be copied to the actual test address. In many cases
>>>>>> + * it's enough to clear/copy the first 8 bytes of the buffer, while the SCCB
>>>>>> + * itself can be larger.
>>>>>> + *
>>>>>> + * Returns true in case of success or false in case of failure
>>>>>> + */
>>>>>> +static bool test_one_simple(uint32_t cmd, uint8_t *addr, uint16_t sccb_len,
>>>>>> + uint16_t buf_len, uint64_t exp_pgm, uint16_t exp_rc)
>>>>>> +{
>>>>>> + memset(sccb_template, 0, sizeof(sccb_template));
>>>>>> + ((SCCBHeader *)sccb_template)->length = sccb_len;
>>>>>> + return test_one_sccb(cmd, addr, buf_len, exp_pgm, exp_rc);
>>>>>
>>>>> Doing a fresh ./configure + make on RHEL7 gives me
>>>>>
>>>>> [linux1@rhkvm01 kvm-unit-tests]$ make
>>>>> gcc -std=gnu99 -ffreestanding -I /home/linux1/git/kvm-unit-tests/lib -I /home/linux1/git/kvm-unit-tests/lib/s390x -I lib -O2 -march=zEC12 -fno-delete-null-pointer-checks -g -MMD -MF s390x/.sclp.d -Wall -Wwrite-strings -Wempty-body -Wuninitialized -Wignored-qualifiers -Werror -fomit-frame-pointer -Wno-frame-address -fno-pic -Wclobbered -Wunused-but-set-parameter -Wmissing-parameter-type -Wold-style-declaration -Woverride-init -Wmissing-prototypes -Wstrict-prototypes -c -o s390x/sclp.o s390x/sclp.c
>>>>> s390x/sclp.c: In function 'test_one_simple':
>>>>> s390x/sclp.c:121:2: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
>>>>> ((SCCBHeader *)sccb_template)->length = sccb_len;
>>>>> ^
>>>>> s390x/sclp.c: At top level:
>>>>> cc1: error: unrecognized command line option "-Wno-frame-address" [-Werror]
>>>>> cc1: all warnings being treated as errors
>>>>> make: *** [s390x/sclp.o] Error 1
>>>>
>>>> The following makes it work:
>>>>
>>>>
>>>> diff --git a/s390x/sclp.c b/s390x/sclp.c
>>>> index c13fa60..0b8117a 100644
>>>> --- a/s390x/sclp.c
>>>> +++ b/s390x/sclp.c
>>>> @@ -117,8 +117,10 @@ static bool test_one_ro(uint32_t cmd, uint8_t *addr, uint64_t exp_pgm, uint16_t
>>>> static bool test_one_simple(uint32_t cmd, uint8_t *addr, uint16_t sccb_len,
>>>> uint16_t buf_len, uint64_t exp_pgm, uint16_t exp_rc)
>>>> {
>>>> + SCCBHeader *header = (void *)sccb_template;
>>>> +
>>>> memset(sccb_template, 0, sizeof(sccb_template));
>>>> - ((SCCBHeader *)sccb_template)->length = sccb_len;
>>>> + header->length = sccb_len;
>>>
>>> While that might silence the compiler warning, we still might get
>>> aliasing problems here, I think.
>>> The right way to solve this problem is to turn sccb_template into a
>>> union of the various structs/arrays that you want to use and then access
>>> the fields through the union instead ("type-punning through union").
>>
>> We do have the exact same thing in lib/s390x/sclp.c already, no?
>
> Maybe we should carefully check that code, too...
>
>> Especially, new compilers don't seem to care?
>
> I've seen horrible bugs due to these aliasing problems in the past -
> without compiler warnings showing up! Certain versions of GCC assume
> that they can re-order code with pointers that point to types of
> different sizes, i.e. in the above example, I think they could assume
> that they could re-order the memset() and the header->length = ... line.
> I'd feel better if we play safe and use a union here.

Should we simply allow type-punning?

--
Thanks,

David / dhildenb