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From:   Muni Sekhar <munisekharrms@gmail.com>
Date:   Sun, 12 Dec 2021 12:34:54 +0530
Message-ID: <CAHhAz+iKepmJGRKzLe+B_XFOax4CzVzeeAB_T5YtZrPgeX8o6g@mail.gmail.com>
Subject: X86 : system call
To:     kernelnewbies <kernelnewbies@kernelnewbies.org>,
        tglx@linutronix.de, Ingo Molnar <mingo@redhat.com>, hpa@zytor.com,
        x86@kernel.org
Cc:     LKML <linux-kernel@vger.kernel.org>
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Hi all,

32-bit system call numbers and entry vectors are defined in the format
"<number> <abi> <name> <entry point> <compat entry point>". What is
the difference between <entry point> and <compat entry point>?

The abi is always "i386" for arch/x86/entry/syscalls/syscall_32.tbl,
whereas for 64-bit(arch/x86/entry/syscalls/syscall_64.tbl) it is used
as "common" and "64", "x32". What is the difference between "common"
and "64", "x32"?

While adding a new system call(for example: mlock) to kernel,
/kernel/sys_ni.c file modified as mentioned below:
+cond_syscall(sys_mlock2);

Why do we pass <entry point> to cond_syscall()?

Also, could someone please point me to a document which explains about
"how to add a new system call" and the "system call flow from user
space to kernel space" in X86 ARCHITECTURE (32-BIT AND 64-BIT).


-- 
Thanks,
Sekhar