linux-kernel - Re: [PATCH 0/3] syscalls: clean up stub naming convention

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Date:   Mon, 9 Apr 2018 08:54:54 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        Maninder Singh <maninder1.s@...sung.com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 0/3] syscalls: clean up stub naming convention

On Mon, Apr 09, 2018 at 08:49:45AM +0200, Ingo Molnar wrote:
> 
> * Dominik Brodowski <linux@...inikbrodowski.net> wrote:
> 
> > +emit_stub() {
> > +    entry="$1"
> > +    if [ "${entry}" != "${entry#__ia32_sys_}" ]; then
> > +	# We need a stub named __ia32_sys which is common to 64-bit
> > +	# except for a different pt_regs layout.
> > +	stubname=${entry#__ia32_sys_}
> > +	echo "#define __IA32_SYS_STUBx_${stubname} __IA32_SYS_STUBx"
> > +	echo "#define ASM_X86_HAS__ia32_sys_${stubname} 1"
> > +    elif [ "$entry" != "${entry#__x32_compat_sys}" ]; then
> > +	# We need a stub named __x32_compat_sys_ which decodes a
> > +	# 64-bit pt_regs and then calls the real syscall function 
> > +	stubname="${entry%%/*}" # handle qualifier
> > +	stubname=${stubname#__x32_compat_sys_} # handle prefix
> > +	echo "#define __X32_COMPAT_SYS_STUBx_${stubname} __X32_COMPAT_SYS_STUBx"
> > +	echo "#define ASM_X86_HAS__x32_compat_sys_${stubname} 1"
> > +    elif [ "$entry" != "${entry#__ia32_compat_sys_x86}" ]; then
> > +	# The compat entry starts with __ia32_compat_sys_x86, so it
> > +	# is a specific x86 compat syscall; no need for __ia32_sys_*()
> > +	stubname=${entry#__ia32_compat_sys_x86_}
> > +	echo "#define __IA32_SYS_STUBx_${stubname} __SYSCALL_STUBx_UNUSED"
> > +	echo "#define ASM_X86_HAS__ia32_sys_${stubname} 1"
> > +    elif [ "$entry" != "${entry#__ia32_compat_sys_}" ]; then
> > +	# The compat entry starts with __ia32_compat_sys, so it is
> > +	# is a generic x86 compat syscall; no need for __ia32_sys_*()
> > +	stubname=${entry#__ia32_compat_sys_}
> > +	echo "#define __IA32_SYS_STUBx_${stubname} __SYSCALL_STUBx_UNUSED"
> > +	echo "#define ASM_X86_HAS__ia32_sys_${stubname} 1"
> > +    fi;
> > +}
> 
> I only have a bikeshed painting comment, even in shell scripts please try to 
> follow the kernel comment style visually, i.e. something like:
> 
> > +    if [ "${entry}" != "${entry#__ia32_sys_}" ]; then
> > +
> > +	#
> > +	# We need a stub named __ia32_sys which is common to 64-bit
> > +	# except for a different pt_regs layout.
> > +	#
> > +	stubname=${entry#__ia32_sys_}
> > +	echo "#define __IA32_SYS_STUBx_${stubname} __IA32_SYS_STUBx"
> > +	echo "#define ASM_X86_HAS__ia32_sys_${stubname} 1"
> > +
> > +    elif [ "$entry" != "${entry#__x32_compat_sys}" ]; then
> > +
> > +	#
> > +	# We need a stub named __x32_compat_sys_ which decodes a
> > +	# 64-bit pt_regs and then calls the real syscall function 
> > +     #
> > +	stubname="${entry%%/*}" # handle qualifier
> > +	stubname=${stubname#__x32_compat_sys_} # handle prefix
> > +	echo "#define __X32_COMPAT_SYS_STUBx_${stubname} __X32_COMPAT_SYS_STUBx"
> > +	echo "#define ASM_X86_HAS__x32_compat_sys_${stubname} 1"
> > +
> > +    elif [ "$entry" != "${entry#__ia32_compat_sys_x86}" ]; then
> > +
> > +     #
> > +	# The compat entry starts with __ia32_compat_sys_x86, so it
> > +	# is a specific x86 compat syscall; no need for __ia32_sys_*()
> > +     #
> > +	stubname=${entry#__ia32_compat_sys_x86_}
> > +	echo "#define __IA32_SYS_STUBx_${stubname} __SYSCALL_STUBx_UNUSED"
> > +	echo "#define ASM_X86_HAS__ia32_sys_${stubname} 1"
> > +
> > +    elif [ "$entry" != "${entry#__ia32_compat_sys_}" ]; then
> > +
> > +     #
> > +	# The compat entry starts with __ia32_compat_sys, so it is
> > +	# is a generic x86 compat syscall; no need for __ia32_sys_*()
> > +     #
> > +	stubname=${entry#__ia32_compat_sys_}
> > +	echo "#define __IA32_SYS_STUBx_${stubname} __SYSCALL_STUBx_UNUSED"
> > +	echo "#define ASM_X86_HAS__ia32_sys_${stubname} 1"
> > +
> > +    fi;
> 
> ( Also note the vertical separation that helps see the overall structure a bit 
>   better. )
> 
> But more fundamentally, that's an awful lot of complex scripting to save 4K 
> (unused) kernel text, not sure it's worth it.

Yes. I just wanted to see myself whether it's worthwile, and it indeed
doesn't seem so. That's exactly why I didn't sign off on it so far...

Thanks,
	Dominik