https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47634
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:0c723bb4be2a67657828b692997855afcdc5d286 commit r13-167-g0c723bb4be2a67657828b692997855afcdc5d286 Author: Marek Polacek <pola...@redhat.com> Date: Thu Mar 31 18:31:39 2022 -0400 c, c++: attribute format on a ctor with a vbase [PR101833, PR47634] Attribute format takes three arguments: archetype, string-index, and first-to-check. The last two specify the position in the function parameter list. r63030 clarified that "Since non-static C++ methods have an implicit this argument, the arguments of such methods should be counted from two, not one, when giving values for string-index and first-to-check." Therefore one has to write struct D { D(const char *, ...) __attribute__((format(printf, 2, 3))); }; However -- and this is the problem in this PR -- ctors with virtual bases also get two additional parameters: the in-charge parameter and the VTT parameter (added in maybe_retrofit_in_chrg). In fact we'll end up with two clones of the ctor: an in-charge and a not-in-charge version (see build_cdtor_clones). That means that the argument position the user specified in the attribute argument will refer to different arguments, depending on which constructor we're currently dealing with. This can cause a range of problems: wrong errors, confusing warnings, or crashes. This patch corrects that; for C we don't have to do anything, and in C++ we can use num_artificial_parms_for. It would be wrong to rewrite the attributes the user supplied, so I've changed POS to be passed by reference so that we don't have to change all the call sites of positional_argument and we still get the default_conversion adjustment. Attribute format_arg is not affected, because it requires that the function returns "const char *" which will never be the case for cdtors. PR c++/101833 PR c++/47634 gcc/c-family/ChangeLog: * c-attribs.cc (positional_argument): Pass POS by reference. Deal with FN being either a function declaration or function type. Use maybe_adjust_arg_pos_for_attribute. * c-common.cc (check_function_arguments): Maybe pass FNDECL down to check_function_format. * c-common.h (maybe_adjust_arg_pos_for_attribute): Declare. (positional_argument): Adjust. * c-format.cc (get_constant): Rename to ... (validate_constant): ... this. Take EXPR by reference. Return bool instead of tree. (handle_format_arg_attribute): Don't overwrite FORMAT_NUM_EXPR by the return value of validate_constant. (decode_format_attr): Don't overwrite FORMAT_NUM_EXPR and FIRST_ARG_NUM_EXPR by the return value of validate_constant. (check_function_format): Adjust a parameter name. (handle_format_attribute): Maybe pass FNDECL down to decode_format_attr. gcc/c/ChangeLog: * c-objc-common.cc (maybe_adjust_arg_pos_for_attribute): New. gcc/cp/ChangeLog: * tree.cc (maybe_adjust_arg_pos_for_attribute): New. gcc/ChangeLog: * tree-core.h (struct attribute_spec): Update comment for HANDLER. gcc/testsuite/ChangeLog: * g++.dg/ext/attr-format-arg1.C: New test. * g++.dg/ext/attr-format1.C: New test. * g++.dg/ext/attr-format2.C: New test. * g++.dg/ext/attr-format3.C: New test.
