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kcov: load acquire coverage count in user-space code

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Update the KCOV documentation to use a load-acquire operation for the
first element of the shared memory buffer between kernel-space and
user-space.

The load-acquire pairs with the write memory barrier used in
kcov_move_area().

[soham.bagchi@utah.edu: v2]
  Link: https://lkml.kernel.org/r/20250803180558.2967962-1-soham.bagchi@utah.edu
Link: https://lkml.kernel.org/r/20250728184318.1839137-2-soham.bagchi@utah.edu
Signed-off-by: Soham Bagchi <soham.bagchi@utah.edu>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Soham Bagchi
2025-07-28 12:43:18 -06:00
committed by Andrew Morton
parent c2fe368b6e
commit 1455b6ac21
1 changed files with 6 additions and 1 deletions
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7
Documentation/dev-tools/kcov.rst
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@@ -361,7 +361,12 @@ local tasks spawned by the process and the global task that handles USB bus #1:
*/
sleep(2);
n = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
/*
* The load to the coverage count should be an acquire to pair with
* pair with the corresponding write memory barrier (smp_wmb()) on
* the kernel-side in kcov_move_area().
*/
n = __atomic_load_n(&cover[0], __ATOMIC_ACQUIRE);
for (i = 0; i < n; i++)
printf("0x%lx\n", cover[i + 1]);
if (ioctl(fd, KCOV_DISABLE, 0))