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+0100, Nick Alcock wrote: > >> On 16 Sep 2025, Kris Van Hees verbalised: > >> > >> > Because alloca pointers are stored internally as offsets into the > >> > scratchmem area, they were printed as small integers. They are > >> > now printed as actual pointer values into kernel space. > >> > > >> > Signed-off-by: Kris Van Hees > >> > >> So... the change is to generate real pointers for children of alloca > >> nodes too, and scalarize more aggressively? I don't really see what the > >> second part has to do with this change (and more specifically why it > >> didn't cause problems before now). > > > > It doesn't cause problems - it is just not what should happen. Since an alloca > > pointer is a pointer into kernel space one would expect (and legacy behaviour > > shows this) that printing it would give us an address value in kernel space. > > Without this patchm we print the *offset* into the scratch memory area, which > > is certainly not a valid pointer in kernel space. > > Ooh true! > > > Because of how code generation is done, it unfortunately requires slightly more > > complex logic to know which values to convert into actual pointer values in > > order to store them in the trace output buffer. An extra complication is that, > > if we are storing the pointer value into the trace event buffer, some versions > > of the verifier will complain if it is a value that is marked as an address > > into a BPF map. That is why it needs to be scalarized. > > Aha, this is saying "if this is not being dereferenced, but instead we > want its literal value" (e.g. for pointer printing) "scalarize it to > lose its mapdom". Presumably we know that the result of such a REF > operation will never be dereferenced, since after scalarization we can't > dereference it? Yes.