linux-kernel - Re: [tip:x86/asm] x86/syscalls: Remove __SYSCALL_COMMON and __SYSCALL

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Date:	Sat, 30 Jan 2016 13:22:05 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>
CC:	Brian Gerst <brgerst@...il.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>,
	tip-bot for Andy Lutomirski <tipbot@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [tip:x86/asm] x86/syscalls: Remove __SYSCALL_COMMON and __SYSCALL_X32

On January 30, 2016 9:35:57 AM PST, Andy Lutomirski <luto@...capital.net> wrote:
>On Sat, Jan 30, 2016 at 1:31 AM, Ingo Molnar <mingo@...nel.org> wrote:
>>
>> * Andy Lutomirski <luto@...capital.net> wrote:
>>
>>> >>>+      if [ "$abi" == "COMMON" -o "$abi" == "64" ]; then
>>> >>>+          # COMMON is the same as 64, except that we don't
>expect X32
>>> >>>+          # programs to use it.  Our expectation has nothing to
>do with
>>> >>>+          # any generated code, so treat them the same.
>>> >>>+          emit 64 "$nr" "$entry" "$compat"
>>> >>>+      elif [ "$abi" == "X32" ]; then
>>> >>>+          # X32 is equivalent to 64 on an X32-compatible kernel.
>>> >>>+          echo "#ifdef CONFIG_X86_X32_ABI"
>>> >>>+          emit 64 "$nr" "$entry" "$compat"
>>> >>>+          echo "#endif"
>>> >>>+      elif [ "$abi" == "I386" ]; then
>>> >>>+          emit "$abi" "$nr" "$entry" "$compat"
>>> >>>+      else
>>> >>>+          echo "Unknown abi $abi" >&2
>>> >>>+          exit 1
>>> >>>+      fi
>>
>>> No combinatorial explosion, please.  We could use __SYSCALL(nr, sym,
>>> abi, qual), though.
>>
>> Mind fixing it, so that we get back the arch-neutral property?
>>
>
>I need some guidance as to the goal to do a good job.
>
>In the version in -tip, I have this thing:
>
>if [ "$abi" == "64" -a -n "$compat" ]; then
>    echo "a compat entry for a 64-bit syscall makes no sense" >&2
>    exit 1
>fi
>
>Moving that outside the script will either be impossible or an
>exercise in really awful C preprocessor hacks.  We could keep that
>under the theory that it's arch-neutral.
>
>It might be nice to add a similar warning that a compat entry for an
>x32 syscall makes so sense.  That's a little less arch-neutral,
>although it wouldn't be actively harmful on any architecture, since
>"x32" wouldn't occur in the first place.
>
>Other than that, I could add a little header called
>syscall_abi_mapping.h containing something like:
>
>#ifndef __SYSCALL_ABI_MAPPING_H
>#define __SYSCALL_ABI_MAPPING_H
>
>#ifdef CONFIG_X86_32
>
>/* Only I386 entries should ever be compiled into 32-bit kernels. */
>#define __SYSCALL_ABI_I386(nr, entry, qual, compat, compat_qual)
>__SYSCALL_I386(nr, entry, qual)
>
>#else
>
>/* I386 entries on 64-bit kernels use the compat entry point. */
>#define __SYSCALL_ABI_I386(nr, entry, qual, compat, compat_qual)
>__SYSCALL_I386(nr, compat, compat_qual)
>
>#define __SYSCALL_ABI_common(nr, entry, compat, qual)
>#define __SYSCALL_ABI_64(nr, entry, qual, compat, compat_qual)
>__SYSCALL_64(nr, entry, qual)
>#ifdef CONFIG_X86_X32
>#define __SYSCALL_ABI_x32(nr, entry, qual, compat, compat_qual)
>__SYSCALL_64(nr, entry, qual)
>#else
>#define __SYSCALL_ABI_x32(nr, entry, qual, compat, compat_qual)
>__SYSCALL_64(nr, entry, qual)
>#endif
>
>#endif
>
>#endif
>
>and teach syscalltbl.sh to emit #include <asm/syscall_abi_mapping.h>
>at the beginning of syscalls_32.h and syscalls_64.h and to reference
>those macros.
>
>hpa, would that meet your requirements?
>
>IMO this is quite a bit messier than the code in -tip, and I'm
>honestly not convinced it's an improvement.
>
>--Andy

Something like that... however, I can't look at in detail right now.
-- 
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