linux-kernel - Re: [PATCH v12 2/3] selftests: tdx: Test TDX attestation GetReport support

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Date:   Fri, 9 Sep 2022 11:40:14 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Wander Lairson Costa <wander@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kai Huang <kai.huang@...el.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v12 2/3] selftests: tdx: Test TDX attestation GetReport
 support



On 9/9/22 6:36 AM, Wander Lairson Costa wrote:
> On Thu, Sep 8, 2022 at 8:45 PM Sathyanarayanan Kuppuswamy
> <sathyanarayanan.kuppuswamy@...ux.intel.com> wrote:
>>
>>
>>
>> On 9/8/22 7:16 AM, Wander Lairson Costa wrote:
>>>> +#ifdef DEBUG
>>>> +static void print_array_hex(const char *title, const char *prefix_str,
>>>> +            const void *buf, int len)
>>>> +{
>>>> +    const __u8 *ptr = buf;
>>>> +    int i, rowsize = HEX_DUMP_SIZE;
>>>> +
>>>> +    if (!len || !buf)
>>>> +            return;
>>>> +
>>>> +    printf("\t\t%s", title);
>>>> +
>>>> +    for (i = 0; i < len; i++) {
>>>> +            if (!(i % rowsize))
>>>> +                    printf("\n%s%.8x:", prefix_str, i);
>>>> +            printf(" %.2x", ptr[i]);
>>>> +    }
>>>> +
>>>> +    printf("\n");
>>>> +}
>>>> +#endif
>>>> +
>>>> +TEST(verify_report)
>>>> +{
>>>> +    __u8 reportdata[TDX_REPORTDATA_LEN];
>>>> +    struct tdreport tdreport;
>>>> +    struct tdx_report_req req;
>>>> +    int devfd, i;
>>>> +
>>>> +    devfd = open(TDX_GUEST_DEVNAME, O_RDWR | O_SYNC);
>>>> +
>>>> +    ASSERT_LT(0, devfd);
>>>> +
>>>> +    /* Generate sample report data */
>>>> +    for (i = 0; i < TDX_REPORTDATA_LEN; i++)
>>>> +            reportdata[i] = i;
>>>> +
>>>> +    /* Initialize IOCTL request */
>>>> +    req.subtype     = 0;
>>>> +    req.reportdata  = (__u64)reportdata;
>>>> +    req.rpd_len     = TDX_REPORTDATA_LEN;
>>>> +    req.tdreport    = (__u64)&tdreport;
>>>> +    req.tdr_len     = sizeof(tdreport);
>>>> +
>>>> +    /* Get TDREPORT */
>>>> +    ASSERT_EQ(0, ioctl(devfd, TDX_CMD_GET_REPORT, &req));
>>>> +
>>>> +#ifdef DEBUG
>>>> +    print_array_hex("\n\t\tTDX report data\n", "",
>>>> +                    reportdata, sizeof(reportdata));
>>>> +
>>>> +    print_array_hex("\n\t\tTDX tdreport data\n", "",
>>>> +                    &tdreport, sizeof(tdreport));
>>>> +#endif
>>> You can unconditionally define print_array_hex, and
>>> use `if (DEBUG)` instead of #ifdef `DEBUG here`. The compiler
>>> will get rid of the unused code when DEBUG is not defined
>>> as expected, but you get the parser to validate it
>>> independent of the definition of DEBUG.
>>
>> Currently, DEBUG is a macro, so we cannot use if (DEBUG) directly.
>> You are suggesting to change DEBUG to a variable? Any reason to
>> make this change? I think both changes are functionally similar.
>> So I am wondering why to make this change?
>>
> 
> My thought is always to define DEBUG. If in debug mode it is defined
> to 1; otherwise to 0.
> Then, you can use `if (DEBUG)` instead of `#ifdef DEBUG`. But the
> former will always check the syntax of the debug code,
> independent of the value of DEBUG, and the compiler will generate the
> same code. The GNU coding standard [1] explains that
> better than I do.
> 
> [1] https://www.gnu.org/prep/standards/standards.html#Conditional-Compilation

Got it. I will use if (DEBUG).

> 
>>>
>>
>> --
>> Sathyanarayanan Kuppuswamy
>> Linux Kernel Developer
>>
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer