bpf zero struct handling testing #8959
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In the kernel we occasionally find empty structs as parameters to functions, for example __io_run_local_work() and its empty typedef struct parameter io_tw_token_t. Ensure that when such structs are used as parameters to functions we handle the fact that no registers are used in their representation for most architectures; s390x is the exception where the usual calling convention register is used [1]. [1] https://lore.kernel.org/bpf/[email protected]/ Signed-off-by: Alan Maguire <[email protected]>
Currently we forbid 0-sized parameters and complain that the function has a malformed void argument, however now that we can handle 0-sized structs using BPF_PROG2(), carve out an exception for them. Also support <= 8 byte return value structs since they can be represented in a register. Signed-off-by: Alan Maguire <[email protected]>
…struct If a 0-length struct is passed as a parameter this throws off assumptions that register N in calling convention will match parameter N. With [1], such function representations will correctly be emitted in BTF because the register/param mismatch is not a result of an optimization we cannot infer from the code alone. Test that BPF_PROG2() macro can handle this situation by having a function with a 0-length struct as first arg and verify that we see expected 2nd, 3rd arg values. Also test that returning a <= 8 byte struct works and we retrieve the correct return value; returning a struct was previously disallowed by the verifier. [1] https://lore.kernel.org/dwarves/[email protected]/ Signed-off-by: Alan Maguire <[email protected]>
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test zero struct handling with CI