Hi Petr, On Tue, 2014-12-02 at 21:42 +0100, Petr Machata wrote: > We now require callers to pass DWARF_GETMACROS_START to start the > iteration. 0 is still accepted, but signals to libdw that the > iteration request comes from an old-style caller, and that opcode 0xff > should be rejected when iterating .debug_macro, to avoid confusion. > [...] > +/* Token layout: > + > + - sign bit is used for distinguishing between .debug_macinfo > + iteration (when unset) and .debug_macro iteration (when set, > + i.e. negative values). The mask is DWARF_GETMACROS_DMACRO. > + > + - the next highest bit is used for distinguishing between callers > + that know that opcode 0xff may have one of two incompatible > + meanings. The mask that we use for selecting this bit is > + DWARF_GETMACROS_START. > + > + Besides, token value of 0 signals end of iteration and -1 is > + reserved for signaling errors. > + > + That means that on a 32-bit machine, 30 bits are allowed for > + offset, and therefore the maximum macro unit size is 1GB. Also, > + because -1 is reserved, it's impossible to represent maximum offset > + of a .debug_macro unit to new-style callers (which in practice > + decreases the permissible macro unit size by another 1 byte). */
I am wondering whether we really need to track both issues with the toke/offset. It looks like we only need to track old-vs-new caller (0xff allowed). Whether we are using macinfo or macro seems to be discoverable from the call made. If the user calls dwarf_getmacros they provide the CU DIE. From that we can determine whether we are using macinfo or macro by looking for the DW_AT_macro_info or DW_AT_macros attribute. If the user calls dwarf_getmacros_off then they are a new style caller by default because that function didn't exist previously. And it only works for macro because it is meant for the transparent_include style macro which doesn't exist with macinfo. Sorry to bring this up after you have written all this code. But if we can use a simpler token encoding then I think we should. Thanks, Mark
