bpf, arm64: relax constraint in BPF JIT compiler #5580
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While introducing support for 9+ arguments for tracing programs on ARM64, commit 9014cf5 ("bpf, arm64: Support up to 12 function arguments") has also introduced a constraint preventing BPF trampolines from being generated if the target function consumes a struct argument passed on stack, because of uncertainties around the exact struct location: if the struct has been marked as packed or with a custom alignment, this info is not reflected in BTF data, and so generated tracing trampolines could read the target function arguments at wrong offsets. This issue is not specific to ARM64: there has been an attempt (see [1]) to bring the same constraint to other architectures JIT compilers. But discussions following this attempt led to the move of this constraint out of the kernel (see [2]): instead of preventing the kernel from generating trampolines for those functions consuming structs on stack, it is simpler to just make sure that those functions with uncertain struct arguments location are not encoded in BTF information, and so that one can not even attempt to attach a tracing program to such function. The task is then deferred to pahole (see [3]). Now that the constraint is handled by pahole, remove it from the arm64 JIT compiler to keep it simple. [1] https://lore.kernel.org/bpf/20250613-deny_trampoline_structs_on_stack-v1-0-5be9211768c3@bootlin.com/ [2] https://lore.kernel.org/bpf/CAADnVQ+sj9XhscN9PdmTzjVa7Eif21noAUH3y1K6x5bWcL-5pg@mail.gmail.com/ [3] https://lore.kernel.org/bpf/[email protected]/ Signed-off-by: Alexis Lothoré (eBPF Foundation) <[email protected]>
Now that the constraint preventing attachment to functions consuming struct on stack has been removed from the kernel (and moved to pahole, with a slightly smarter detection, to prevent only those that are packed), re-enable the tracing_struct tests for arm64. Signed-off-by: Alexis Lothoré (eBPF Foundation) <[email protected]>
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Pull request for series with
subject: bpf, arm64: relax constraint in BPF JIT compiler
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=980393