On Thu, Sep 18, 2025 at 09:20:52AM +0200, Martin Uecker wrote:
> Am Mittwoch, dem 17.09.2025 um 17:56 +0000 schrieb Qing Zhao:
> > Hi,
> >
> > > On Sep 13, 2025, at 19:23, Kees Cook <[email protected]> wrote:
> > >
> > > To support the KCFI typeid and future type-based allocators,
>
> What I find problematic though is that this is not based on GNU / ISO C
> rules but on stricter Linux kernel rules. I think such builtin should
> have two versions.
>
> So maybe
>
> __builtin_typeinfo_hash_strict // strict
> __builtin_typeinfo_hash_canonical // standard
>
> or similar, or maybe instead have a flag argument so that we can
> other options which may turn out to be important in the future
> (such as ignoring qualifiers or supporting newer languag features).
Can you send me a patch to gcc/testsuite/gcc.dg/builtin-typeinfo.c
that shows what differences you mean? Because AFAICT, this C version
matches the C++ typeinfo implementation. There isn't a need for these
hashes to be comparable in a way that they could be used to, for
example, reimplement __builtin_types_compatible_p. It's called
"typeinfo" and that has a specific meaning currently...
Given:
typedef int arr10[10];
typedef int arr_unknown[];
typedef int *arr;
typedef struct named { int a; int b; } named_t;
typedef struct { int a; int b; } nameless_t;
typedef void (*func_arr10)(int[10]);
typedef void (*func_arr_unknown)(int[]);
typedef void (*func_ptr)(int*);
typedef void (*func_named(named_t*);
typedef void (*func_nameless(nameless_t*);
C++ typeinfo(...).name() shows:
int[10]: A10_i
int[]: A_i
int *: Pi
named_t: 5named
nameless_t: 10nameless_t
void(*)(int[10]): PFvPiE
void(*)(int[]): PFvPiE
void(*)(int*): PFvPiE
void(*)(named_t*): PFvP5namedE
void(*)(nameless_t*): PFvP10nameless_tE
This __builtin_typeinfo_name(...) shows:
int[10]: A10_i
int[]: A_i
int *: Pi
__builtin_compatible_types_p(int[10], int[]): true
__builtin_compatible_types_p(int[], int*): false
named_t: 5named
nameless_t: 10nameless_t
void(*)(int[10]): PFvPiE
void(*)(int[]): PFvPiE
void(*)(int*): PFvPiE
void(*)(named_t*): PFvP5namedE
void(*)(nameless_t*): PFvP10nameless_tE
What would you want the "Strict ISO C" builtin to do instead?
-Kees
--
Kees Cook
