Re: [PATCH] selftests/sgx: Fix corrupted cpuid macro invocation

From: Reinette Chatre <reinette.chatre@intel.com>
To: Jarkko Sakkinen <jarkko@kernel.org>, Shuah Khan <shuah@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	<linux-kselftest@vger.kernel.org>, <linux-sgx@vger.kernel.org>
Subject: Re: [PATCH] selftests/sgx: Fix corrupted cpuid macro invocation
Date: Sat, 4 Dec 2021 16:32:59 -0800	[thread overview]
Message-ID: <c5792b66-4a27-0a62-bb75-6cc0c4219002@intel.com> (raw)
In-Reply-To: <20211204202355.23005-1-jarkko@kernel.org>

Hi Jarkko,

(Dave: I am very sorry - selftests on x86/sgx on tip.git is currently 
broken because of this)

On 12/4/2021 12:23 PM, Jarkko Sakkinen wrote:
> Compilation results:
> 
> $ make -C tools/testing/selftests/sgx/
> make: Entering directory '/home/jarkko/Projects/linux-sgx/tools/testing/selftests/sgx'
> gcc -Wall -Werror -g -I../../../../tools/include -fPIC -z noexecstack -c main.c -o /home/jarkko/Projects/linux-sgx/tools/testing/selftests/sgx/main.o
> main.c: In function ‘get_total_epc_mem’:
> main.c:296:17: error: implicit declaration of function ‘__cpuid’ [-Werror=implicit-function-declaration]
>    296 |                 __cpuid(&eax, &ebx, &ecx, &edx);
>        |                 ^~~~~~~
> cc1: all warnings being treated as errors
> make: *** [Makefile:33: /home/jarkko/Projects/linux-sgx/tools/testing/selftests/sgx/main.o] Error 1
> make: Leaving directory '/home/jarkko/Projects/linux-sgx/tools/testing/selftests/sgx'
> 
> Include to cpuid.h is missing and the macro usage is incorrect.
> 
> Include cpuid.h and use __cpuid_count() macro in order to fix the
> compilation issue.
> 
> Fixes: f0ff2447b861 ("selftests/sgx: Add a new kselftest: Unclobbered_vdso_oversubscribed")
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

I am sorry - this was my mistake because of a last minute change to that 
patch that I submitted with a dependency that only arrives in a later 
patch that is not upstream yet.

Jarkko, thank you very much for catching this.

I am not sure what the right way is to fix it though - my original 
intention, what the code uses, was to add a snippet as below as is the 
custom for all tests needing to run cpuid. There are many usages of 
cpuid among the selftests but none rely on the cpuid.h to bring in 
__cpuid_count. I do not know the motivation for this but preferred to 
stick with the custom for my implementation.

+static inline void __cpuid(unsigned int *eax, unsigned int *ebx,
+			   unsigned int *ecx, unsigned int *edx)
+{
+	asm volatile("cpuid"
+	    : "=a" (*eax),
+	      "=b" (*ebx),
+	      "=c" (*ecx),
+	      "=d" (*edx)
+	    : "0" (*eax), "2" (*ecx)
+	    : "memory");
+}

Reinette