The direct-call syscall dispatch function doesn't know that the exit()
and exit_group() syscall handlers don't return, so the call sites aren't
optimized accordingly.

Fix that by marking the exit syscall declarations __noreturn.

Fixes the following warnings:

  vmlinux.o: warning: objtool: x64_sys_call+0x2804: __x64_sys_exit() is missing a __noreturn annotation
  vmlinux.o: warning: objtool: ia32_sys_call+0x29b6: __ia32_sys_exit_group() is missing a __noreturn annotation

Fixes: 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system calls")
Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/5d8882bc077d8eadcc7fd1740b56dfb781f12288.1719381528.git.jpoimboe@kernel.org

Currently, syscall{hdr,tbl}.sh sorts the entire syscall table, but you
can assume it is already sorted by the syscall number.

The generated syscall table does not work if the same syscall number
appears twice. Check it in the script.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Most of architectures generate syscall headers at the compile time
in a similar way.

The syscall table has the same format for all architectures. Each line
has up to 5 fields; syscall number, ABI, syscall name, native entry
point, and compat entry point. The syscall table is processed by
syscalltbl.sh script into header files.

Despite the same pattern, scripts are maintained per architecture,
which results in code duplication and bad maintainability.

As of v5.11-rc1, 12 architectures duplicate similar shell scripts:

  $ find arch -name syscalltbl.sh | sort
  arch/alpha/kernel/syscalls/syscalltbl.sh
  arch/arm/tools/syscalltbl.sh
  arch/ia64/kernel/syscalls/syscalltbl.sh
  arch/m68k/kernel/syscalls/syscalltbl.sh
  arch/microblaze/kernel/syscalls/syscalltbl.sh
  arch/mips/kernel/syscalls/syscalltbl.sh
  arch/parisc/kernel/syscalls/syscalltbl.sh
  arch/powerpc/kernel/syscalls/syscalltbl.sh
  arch/sh/kernel/syscalls/syscalltbl.sh
  arch/sparc/kernel/syscalls/syscalltbl.sh
  arch/x86/entry/syscalls/syscalltbl.sh
  arch/xtensa/kernel/syscalls/syscalltbl.sh

My goal is to unify them into scripts/syscalltbl.sh.

__SYSCALL_WITH_COMPAT should be defined as follows:

32-bit kernel:
  #define __SYSCALL_WITH_COMPAT(nr, native, compat) __SYSCALL(nr, native)

64-bit kernel:

  #define __SYSCALL_WITH_COMPAT(nr, native, compat) __SYSCALL(nr, compat)

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>