linux-kernel - Re: [RFC v2] bpf.2: Use standard types and attributes

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Date:   Tue, 4 May 2021 17:53:29 +0200
From:   "Alejandro Colomar (man-pages)" <alx.manpages@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        linux-man <linux-man@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        glibc <libc-alpha@...rceware.org>, GCC <gcc-patches@....gnu.org>,
        bpf <bpf@...r.kernel.org>,
        David Laight <David.Laight@...lab.com>,
        Zack Weinberg <zackw@...ix.com>,
        Joseph Myers <joseph@...esourcery.com>
Subject: Re: [RFC v2] bpf.2: Use standard types and attributes

Hi Greg and Alexei,

> On Tue, May 04, 2021 at 07:12:01AM -0700, Alexei Starovoitov wrote:
>> For the same reasons as explained earlier:
>> Nacked-by: Alexei Starovoitov <ast@...nel.org>

Okay, I'll add that.

On 5/4/21 4:24 PM, Greg KH wrote:> I agree, the two are not the same 
type at all, this change should not be
> accepted.

I get that in the kernel you don't use the standard fixed-width types 
(with some exceptions), probably not to mess with code that relies on 
<stdint.h> not being included (I hope there's not much code that relies 
on this in 2021, but who knows).

But, there is zero difference between these types, from the point of 
view of the compiler.  There's 100% compatibility between those types, 
and you're able to mix'n'match them.  See some example below.

Could you please explain why the documentation, which supposedly only 
documents the API and not the internal implementation, should not use 
standard naming conventions?  The standard is much easier to read for 
userspace programmers, which might ignore why the kernel does some 
things in some specific ways.

BTW, just to clarify, bpf.2 is just a small sample to get reviews; the 
original intention was to replace __uNN by uintNN_t in all of the manual 
pages.

Thanks,

Alex

...

Example:

$ cat test.c
#include <stdint.h>

typedef int __s32;

int32_t foo(void);

int main(void)
{
	return 1 - foo();
}

__s32 foo(void)
{
	return 1;
}
$ cc -Wall -Wextra -Werror -S -Og test.c -o test.s
$ cat test.s
	.file	"test.c"
	.text
	.globl	foo
	.type	foo, @function
foo:
.LFB1:
	.cfi_startproc
	movl	$1, %eax
	ret
	.cfi_endproc
.LFE1:
	.size	foo, .-foo
	.globl	main
	.type	main, @function
main:
.LFB0:
	.cfi_startproc
	call	foo
	movl	%eax, %edx
	movl	$1, %eax
	subl	%edx, %eax
	ret
	.cfi_endproc
.LFE0:
	.size	main, .-main
	.ident	"GCC: (Debian 10.2.1-6) 10.2.1 20210110"
	.section	.note.GNU-stack,"",@progbits
$

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/