Exercise generic output buffers with and without CAP_PERFMON, using both helpers and __uninit kfuncs. Check that initialized bytes stay readable and lose stale value information, while invalid bytes remain unreadable without permission to read uninitialized stack memory. Cover constant and variable sizes, scalar spills, pointer spills, special stack objects, and privileged variable offsets. Add a kfunc that writes only the first byte of its output. Its runtime tests read preinitialized bytes, checking both the written byte and an untouched tail byte across a liveness checkpoint. Verify that the sysctl name helper and uninitialized fixed and variable-sized kfunc outputs are accepted when their contents are not read back. Update existing __uninit readback expectations and exercise skb_load_bytes with reduced capabilities. Even fully-writing generic outputs now preserve invalid bytes in the verifier, so reading those bytes requires prior initialization by the BPF program. Use map_update_elem inputs for helper_arg_fallback_keeps_scanning. Its original snprintf argument no longer reads the buffer, and a privileged output with an unknown size does not trigger the whole-stack read fallback. A variable-offset key and parent-frame value retain the intended assertion. Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://patch.msgid.link/20260921023843.411943-10-memxor@gmail.com