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

Alejandro Colomar (man-pages)
2021-05-04T15:53:36Z

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@kernel.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/