linux-kernel - Re: [PATCH] selftests: vDSO: Do not rely on $ARCH for vdso_test_getrandom && vdso_test

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Message-ID: <ffc5600d-362f-4400-8f8b-a1ea77ca51bf@csgroup.eu>
Date: Mon, 2 Sep 2024 15:23:47 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Mark Brown <broonie@...nel.org>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org,
 Adhemerval Zanella <adhemerval.zanella@...aro.org>,
 Xi Ruoyao <xry111@...111.site>
Subject: Re: [PATCH] selftests: vDSO: Do not rely on $ARCH for
 vdso_test_getrandom && vdso_test_chacha

Le 02/09/2024 à 14:37, Mark Brown a écrit :
> On Mon, Sep 02, 2024 at 02:22:38PM +0200, Christophe Leroy wrote:
> 
>> When vdso_test_getcpu doesn't find the vDSO entry point, it prints an error
>> text and returns KSFT_SKIP
> 
>> I thought it would be more correct to have the same behaviour on
>> vdso_test_getrandom instead of trying to build it only when the underlying
>> kernel supports it.
> 
> The problem is that the test incorporates assembler code so it simply
> won't build for architectures without explicit porting, the issue isn't
> if the target kernel supports it but rather that the test won't compile
> in the first place.

Yes indeed and that was the purpose of my patch, have a macro in 
vdso_config.h to tell where the assembler code is:

diff --git a/tools/testing/selftests/vDSO/vdso_config.h 
b/tools/testing/selftests/vDSO/vdso_config.h
index 740ce8c98d2e..693920471160 100644
--- a/tools/testing/selftests/vDSO/vdso_config.h
+++ b/tools/testing/selftests/vDSO/vdso_config.h
@@ -47,6 +47,7 @@
  #elif defined(__x86_64__)
  #define VDSO_VERSION		0
  #define VDSO_NAMES		1
+#define VDSO_GETRANDOM	 
"../../../../arch/x86/entry/vdso/vgetrandom-chacha.S"
  #elif defined(__riscv__) || defined(__riscv)
  #define VDSO_VERSION		5
  #define VDSO_NAMES		1

And then:

diff --git a/tools/testing/selftests/vDSO/vdso_test_chacha-asm.S 
b/tools/testing/selftests/vDSO/vdso_test_chacha-asm.S
new file mode 100644
index 000000000000..8e704165f6f2
--- /dev/null
+++ b/tools/testing/selftests/vDSO/vdso_test_chacha-asm.S
@@ -0,0 +1,7 @@
+#include "vdso_config.h"
+
+#ifdef VDSO_GETRANDOM
+
+#include VDSO_GETRANDOM
+
+#endif

I thought it was a lot easier to handle if through necessary #ifdefs in 
vdso_config.h that implementing an additional logic in Makefiles.

Christophe