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

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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@xxxxxxxxxxxxx>
>>>>>> Reviewed-by: Thomas Huth <thuth@xxxxxxxxxx>
>>>>>> Acked-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
>>>>>> ---
>>>>>>  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@xxxxxxxxxxxxx>
>>>>>> + *
>>>>>> + * 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




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