On 03/12/18 11:40, Paolo Abeni wrote: > This header define a bunch of helpers that allow avoiding the > retpoline overhead when calling builtin functions via function pointers. > It boils down to explicitly comparing the function pointers to > known builtin functions and eventually invoke directly the latter. > > The macros defined here implement the boilerplate for the above schema > and will be used by the next patches. > > rfc -> v1: > - use branch prediction hint, as suggested by Eric > > Suggested-by: Eric Dumazet <Eric Dumazet eduma...@google.com> > Signed-off-by: Paolo Abeni <pab...@redhat.com> > --- I'm not sure I see the reason why this is done with numbers and 'name ## NR', adding extra distance between the callsite and the list of callees. In particular it means that each callable needs to specify its index. Wouldn't it be simpler just to have #define INDIRECT_CALL_1(f, f1, ...) \ (likely(f == f1) ? f1(__VA_ARGS__) : f(__VA_ARGS__)) #define INDIRECT_CALL_2(f, f2, f1, ...) \ (likely(f == f2) ? f2(__VA_ARGS__) : INDIRECT_CALL_1(f, f1, __VA_ARGS__)) etc.? Removing the need for INDIRECT_CALLABLE_DECLARE_* entirely.
At least the commit message should explain the rationale for not doing things this way. -Ed PS: this has reminded me of my desire to try runtime creation of these kinds of branch tables with self-modifying code; is there any documentation on how to go about writing to kernel .text at runtime? Last time I had a try at it I got very confused.
