Possible typo/redundancy in mmap(2) SYNOPSIS

Possible typo/redundancy in mmap(2) SYNOPSIS

[佐々木龍路]

1. Where: mmap(2) SYNOPSIS section.
2. Issue: There is a semicolon after length and it appears twice,
which looks like the function has an extra argument.
3.Actual display: void *mmap(size_t length;void addr[length],size_t length,...);
4. Why it's confusing: From a syscall ABI perspective, rdi should be
addr, not length. This notation might confuse users about the actual
number of arguments.
man 2.13.1

Re: Possible typo/redundancy in mmap(2) SYNOPSIS

[Alejandro Colomar]

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Hi,

On 2026-04-12T23:11:47+0900, 佐々木龍路 wrote:
> 1. Where: mmap(2) SYNOPSIS section.
> 2. Issue: There is a semicolon after length and it appears twice,
> which looks like the function has an extra argument.

This is correct.  That's a forward declaration of a function parameter.
They're documented here:

<https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html>


Have a lovely day!
Alex

> 3.Actual display: void *mmap(size_t length;void addr[length],size_t length,...);
> 4. Why it's confusing: From a syscall ABI perspective, rdi should be
> addr, not length. This notation might confuse users about the actual
> number of arguments.
> man 2.13.1
> 

-- 
<https://www.alejandro-colomar.es>

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