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Subject[PATCH] kcov: fix struct layout for kcov_remote_arg
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Make the layout of kcov_remote_arg the same for 32-bit and 64-bit code.
This makes it more convenient to write userspace apps that can be compiled
into 32-bit or 64-bit binaries and still work with the same 64-bit kernel.
Also use proper __u32 types in uapi headers instead of unsigned ints.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---

Hi Andrew,

We've noticed failures on 32 bit syzbot instances when the kcov patches
got merged into mainline. The reason is that the layout of kcov_remote_arg
depends on the alignment rules, which are different for 32/64 bit code.
We can deal with this issue in syzkaller [1], but I think it would be
cleander to get this fixed in the kernel.

I hope this patch is acceptable, since the change has just been merged and
is not included into a release kernel version. The patch breaks the newly
introduced kcov API for 32 bit apps.

Sorry for not testing it with 32 bit code earlier.

Thanks!

[1] https://github.com/google/syzkaller/commit/ba97c611a36b7729d489ebca5f97183c2ba7a90a

Documentation/dev-tools/kcov.rst | 7 ++++---
include/uapi/linux/kcov.h | 11 ++++++-----
2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst
index 36890b026e77..744df2bae1ed 100644
--- a/Documentation/dev-tools/kcov.rst
+++ b/Documentation/dev-tools/kcov.rst
@@ -251,9 +251,10 @@ selectively from different subsystems.
.. code-block:: c

struct kcov_remote_arg {
- unsigned trace_mode;
- unsigned area_size;
- unsigned num_handles;
+ uint32_t trace_mode;
+ uint32_t area_size;
+ uint32_t num_handles;
+ uint32_t reserved;
uint64_t common_handle;
uint64_t handles[0];
};
diff --git a/include/uapi/linux/kcov.h b/include/uapi/linux/kcov.h
index 409d3ad1e6e2..53267f9f1665 100644
--- a/include/uapi/linux/kcov.h
+++ b/include/uapi/linux/kcov.h
@@ -9,11 +9,12 @@
* and the comment before kcov_remote_start() for usage details.
*/
struct kcov_remote_arg {
- unsigned int trace_mode; /* KCOV_TRACE_PC or KCOV_TRACE_CMP */
- unsigned int area_size; /* Length of coverage buffer in words */
- unsigned int num_handles; /* Size of handles array */
- __u64 common_handle;
- __u64 handles[0];
+ __u32 trace_mode; /* KCOV_TRACE_PC or KCOV_TRACE_CMP */
+ __u32 area_size; /* Length of coverage buffer in words */
+ __u32 num_handles; /* Size of handles array */
+ __u32 reserved;
+ __u64 common_handle;
+ __u64 handles[0];
};

#define KCOV_REMOTE_MAX_HANDLES 0x100
--
2.24.0.393.g34dc348eaf-goog
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