On Fri, Mar 6, 2020 at 2:04 AM Martin Sebor <mse...@gmail.com> wrote:
>
> Treating incompatible redeclarations of built-in functions as built-ins
> is a problem not just for the middle-end but even for the C front-end
> itself, when different parts of it make different assumptions about
> what is and isn't valid. The test case that is the subject of this
> bug report (a GCC 9 and 10 regression) is one such example: it shows
> that the attribute format validation assumes the function declaration
> the attribute applies to has passed the prerequisite validation. But
> that's not the case when the function is an incompatibly redeclared
> built-in where a format attribute's positional argument refers to
> parameter of an invalid/nonsensical type.
>
> The attached patch further adjusts the front-end to consider even more
> incompatible redeclarations as built-ins: in particular, redeclarations
> whose pointer arguments point to incompatible variants of unqualified
> types (e.g., char* vs int*, though not char* vs const char*).
>
> Besides avoiding the front-end and some middle-end ICEs, the effect
> of the patch is also to diagnose more incompatible redeclarations
> of built-ins than before, but fewer invalid calls to such functions
> (since they're no longer considered built-ins). That seems like
> an unavoidable trade-off.
>
> Tested on x86_64-linux. Is this acceptable for GCC 10? How about 9?
The actual patch needs reviewing from a FE maintainer but I'd support
putting this in for GCC 10.
It would be nice if we can put in code like the following to catch "bogus"
built-in declarations. I've put it in call verification because there it's
where it matters most, free-lang-data would be another canonical place
which would then process all "reachable" function declarations but we
don't yet call free-lang-data when not doing LTO.
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index f7b817d94e6..ae695891bd4 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -3356,6 +3356,17 @@ verify_gimple_call (gcall *stmt)
return true;
}
+ if (fndecl
+ && fndecl_built_in_p (fndecl, BUILT_IN_NORMAL)
+ && !types_compatible_p (TREE_TYPE (fndecl),
+ TREE_TYPE (builtin_decl_explicit
+ (DECL_FUNCTION_CODE (fndecl)))))
+ {
+ error ("function declaration declared built-in but does not "
+ "match expected type");
+ return true;
+ }
+
tree lhs = gimple_call_lhs (stmt);
if (lhs
&& (!is_gimple_lvalue (lhs)
> Martin
