On 10/17/18 9:13 AM, Edward Cree wrote: > On 17/10/18 08:23, Yonghong Song wrote: >> This patch adds BTF_KIND_FUNC and BTF_KIND_FUNC_PROTO >> support to the type section. BTF_KIND_FUNC_PROTO is used >> to specify the type of a function pointer. With this, >> BTF has a complete set of C types (except float). >> >> BTF_KIND_FUNC is used to specify the signature of a >> defined subprogram. BTF_KIND_FUNC_PROTO can be referenced >> by another type, e.g., a pointer type, and BTF_KIND_FUNC >> type cannot be referenced by another type. > Why are distinct kinds created for these? A function body is > a value of function type, and since there's no way (in C) to > declare a variable of function type (only pointer-to- > function), any declaration of function type must necessarily > be a BTF_KIND_FUNC, whereas any other reference to a function > type (e.g. a declaration of type pointer to function type) > must, as you state above, be a BTF_KIND_FUNC_PROTO. > In fact, you can tell the difference just from name_off, since > a (C-legal) BTF_KIND_FUNC_PROTO will always be anonymous (as > the pointee of a pointer type), while a BTF_KIND_FUNC will > have the name of the subprogram.
What you stated is true, BTF_KIND_FUNC_PROTO corresponds to dwarf subroutine tag which has no name while BTF_KIND_FUNC must have a valid name. The original design is to have both since they are corresponding to different dwarf constructs. Martin, what do you think? > > -Ed >
