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author | Marco Elver <elver@google.com> | 2021-04-22 22:18:22 +0300 |
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committer | Peter Zijlstra <peterz@infradead.org> | 2021-04-23 10:03:16 +0300 |
commit | 3ddb3fd8cdb0a6c11b7c8d91ba42d84c4ea3cc43 (patch) | |
tree | 458583355f514c9ce5e4d9bba961ce02c0e71583 /tools/testing/selftests | |
parent | 32d35c4a96ec79446f0d7be308a6eb248b507a0b (diff) | |
download | linux-3ddb3fd8cdb0a6c11b7c8d91ba42d84c4ea3cc43.tar.xz |
signal, perf: Fix siginfo_t by avoiding u64 on 32-bit architectures
The alignment of a structure is that of its largest member. On
architectures like 32-bit Arm (but not e.g. 32-bit x86) 64-bit integers
will require 64-bit alignment and not its natural word size.
This means that there is no portable way to add 64-bit integers to
siginfo_t on 32-bit architectures without breaking the ABI, because
siginfo_t does not yet (and therefore likely never will) contain 64-bit
fields on 32-bit architectures. Adding a 64-bit integer could change the
alignment of the union after the 3 initial int si_signo, si_errno,
si_code, thus introducing 4 bytes of padding shifting the entire union,
which would break the ABI.
One alternative would be to use the __packed attribute, however, it is
non-standard C. Given siginfo_t has definitions outside the Linux kernel
in various standard libraries that can be compiled with any number of
different compilers (not just those we rely on), using non-standard
attributes on siginfo_t should be avoided to ensure portability.
In the case of the si_perf field, word size is sufficient since there is
no exact requirement on size, given the data it contains is user-defined
via perf_event_attr::sig_data. On 32-bit architectures, any excess bits
of perf_event_attr::sig_data will therefore be truncated when copying
into si_perf.
Since si_perf is intended to disambiguate events (e.g. encoding relevant
information if there are more events of the same type), 32 bits should
provide enough entropy to do so on 32-bit architectures.
For 64-bit architectures, no change is intended.
Fixes: fb6cc127e0b6 ("signal: Introduce TRAP_PERF si_code and si_perf to siginfo")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lkml.kernel.org/r/20210422191823.79012-1-elver@google.com
Diffstat (limited to 'tools/testing/selftests')
-rw-r--r-- | tools/testing/selftests/perf_events/sigtrap_threads.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/tools/testing/selftests/perf_events/sigtrap_threads.c b/tools/testing/selftests/perf_events/sigtrap_threads.c index 9c0fd442da60..78ddf5e11625 100644 --- a/tools/testing/selftests/perf_events/sigtrap_threads.c +++ b/tools/testing/selftests/perf_events/sigtrap_threads.c @@ -44,7 +44,7 @@ static struct { } ctx; /* Unique value to check si_perf is correctly set from perf_event_attr::sig_data. */ -#define TEST_SIG_DATA(addr) (~(uint64_t)(addr)) +#define TEST_SIG_DATA(addr) (~(unsigned long)(addr)) static struct perf_event_attr make_event_attr(bool enabled, volatile void *addr) { |