Messages in this thread | | | Date | Sun, 14 Nov 2021 16:45:17 +0100 | Subject | Re: [PATCH v16 1/3] fs: Add trusted_for(2) syscall implementation and related sysctl | From | "Alejandro Colomar (man-pages)" <> |
| |
Hi Geert,
On 11/14/21 16:32, Geert Uytterhoeven wrote: > Hi Alejandro, > > On Sat, Nov 13, 2021 at 8:56 PM Alejandro Colomar (man-pages) > <alx.manpages@gmail.com> wrote: >> On 11/13/21 14:02, Mickaël Salaün wrote: >>>> TL;DR: >>>> >>>> ISO C specifies that for the following code: >>>> >>>> enum foo {BAR}; >>>> >>>> enum foo foobar; >>>> >>>> typeof(foo) shall be int >>>> typeof(foobar) is implementation-defined >>> >>> I tested with some version of GCC (from 4.9 to 11) and clang (10 and 11) >>> with different optimizations and the related sizes are at least the same >>> as for the int type. >> >> GCC has -fshort-enums to make enum types be as short as possible. I >> expected -Os to turn this on, since it saves space, but it doesn't. > > Changing optimization level must not change the ABI, else debugging > would become even more of a nightmare.
I agree, but if you invoke implementation-defined, then it's not (only) the compiler's fault.
Instead of not allowing GCC to enable -fshort-enums ever, one can write ISO C-complying code in the parts that will be exposed as an interface, by just using int.
That allows using -fshort-enums for whatever reasons it might be good.
Not saying that the kernel wants to enable it, but it costs nothing to write non-implementation-defined code that doesn't forbid it.
It's comparable to passing a struct (not a pointer to it) to a function. If you change the size of the struct, you screw the interface. Better pass pointers, or standard types.
Cheers, Alex
-- Alejandro Colomar Linux man-pages comaintainer; http://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/
| |