From: Rich Felker <dalias@libc.org>
To: "Jₑₙₛ Gustedt" <jens.gustedt@inria.fr>
Cc: musl@lists.openwall.com, jens.gustedt@posteo.eu
Subject: Re: [musl] [C23 printf 2/3] C23: implement the wN length specifiers for printf
Date: Fri, 2 Jun 2023 11:16:40 -0400 [thread overview]
Message-ID: <20230602151639.GS4163@brightrain.aerifal.cx> (raw)
In-Reply-To: <20230602170926.41dca6e7@inria.fr>
On Fri, Jun 02, 2023 at 05:09:26PM +0200, Jₑₙₛ Gustedt wrote:
> Rich,
>
> on Fri, 2 Jun 2023 10:38:00 -0400 you (Rich Felker <dalias@libc.org>)
> wrote:
>
> > The logic here for whether w64 is LPRE or LLPRE is wrong. The
> > condition for whether [u]int64_t is long or long long is not whether
> > uintptr_t or long long would be too wide (they never are, in our ABIs)
> > but whether long is long enough. All our [u]intN_t are the lowest-rank
> > type of the desired size, and this seems to be consistent with what
> > other implementations like glibc do.
>
> I probably copied that logic wrong from somewhere. Yes, right thing is
> probably just to compare to the new `ULONG_WIDTH` macro or so.
>
> One thing to think about could be to always map 64 to `long long`,
> just for this function here. This would always have the right size and
> representation. And since this is an implementation of the C library,
> we make the rules ;-)
Well, in musl we generally want the code to have well-defined behavior
even if it's inlined via LTO, where the types would mismatch. Note
that this is kinda a problem for scanf where va_arg is used with
void*, except that POSIX, conveniently, explicitly requires the C
(compiler) implementation accept mismatched va_arg types when both
types are pointers. This is a big hammer but it seems to be a
necessary assumption to admit implementing the %n$ form of scanf,
which POSIX requires.
Rich
next prev parent reply other threads:[~2023-06-02 15:16 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1685429467.git.Jens.Gustedt@inria.fr>
2023-05-30 6:55 ` [musl] [C23 printf 1/3] C23: implement the b and B printf specifiers Jens Gustedt
2023-05-30 6:55 ` [musl] [C23 printf 2/3] C23: implement the wN length specifiers for printf Jens Gustedt
2023-06-02 14:38 ` Rich Felker
2023-06-02 15:09 ` Jₑₙₛ Gustedt
2023-06-02 15:16 ` Rich Felker [this message]
2023-06-02 15:37 ` Jₑₙₛ Gustedt
2023-05-30 6:55 ` [musl] [C23 printf 3/3] C23: implement the wfN length modifiers " Jens Gustedt
2023-05-31 14:04 [musl] [C23 printf 0/3] to be replaced Jens Gustedt
2023-05-31 14:04 ` [musl] [C23 printf 2/3] C23: implement the wN length specifiers for printf Jens Gustedt
-- strict thread matches above, loose matches on Subject: below --
2023-05-26 19:41 [musl] [C23 printf 0/3] Jens Gustedt
2023-05-26 19:41 ` [musl] [C23 printf 2/3] C23: implement the wN length specifiers for printf Jens Gustedt
2023-05-26 20:31 ` Rich Felker
2023-05-26 20:51 ` Jₑₙₛ Gustedt
2023-05-26 21:03 ` Rich Felker
2023-05-29 7:14 ` Jₑₙₛ Gustedt
2023-05-29 15:46 ` Rich Felker
2023-05-29 19:21 ` Jₑₙₛ Gustedt
2023-05-30 1:48 ` Rich Felker
2023-05-30 6:46 ` Jₑₙₛ Gustedt
2023-05-30 17:28 ` Rich Felker
2023-05-30 18:00 ` Rich Felker
2023-05-31 7:59 ` Jₑₙₛ Gustedt
2023-06-02 14:29 ` Rich Felker
2023-06-02 14:55 ` Jₑₙₛ Gustedt
2023-06-02 15:07 ` Rich Felker
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