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x86/syscalls: Document the fact that syscalls 512-547 are a legacy mistake 

Since this commit:

  6365b842aa ("x86/syscalls: Split the x32 syscalls into their own table")

there is no need for special x32-specific syscall numbers.  I forgot to
update the comments in syscall_64.tbl.  Add comments to make it clear to
future contributors that this range is a legacy wart.

Reported-by: Jessica Clarke <jrtc27@jrtc27.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/6c56fb4ddd18fc60a238eb4d867e4b3d97c6351e.1602471055.git.luto@kernel.org
This commit is contained in:
Andy Lutomirski 2020-10-11 19:51:21 -07:00 committed by Ingo Molnar
parent f2ac57a4c4
commit c3b484c439
1 changed files with 6 additions and 4 deletions
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10
arch/x86/entry/syscalls/syscall_64.tbl
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@ -363,10 +363,10 @@
439 common faccessat2 sys_faccessat2
#
# x32-specific system call numbers start at 512 to avoid cache impact
# for native 64-bit operation. The __x32_compat_sys stubs are created
# on-the-fly for compat_sys_*() compatibility system calls if X86_X32
# is defined.
# Due to a historical design error, certain syscalls are numbered differently
# in x32 as compared to native x86_64. These syscalls have numbers 512-547.
# Do not add new syscalls to this range. Numbers 548 and above are available
# for non-x32 use.
#
512 x32 rt_sigaction compat_sys_rt_sigaction
513 x32 rt_sigreturn compat_sys_x32_rt_sigreturn
@ -404,3 +404,5 @@
545 x32 execveat compat_sys_execveat
546 x32 preadv2 compat_sys_preadv64v2
547 x32 pwritev2 compat_sys_pwritev64v2
# This is the end of the legacy x32 range. Numbers 548 and above are
# not special and are not to be used for x32-specific syscalls.