On Mon, Dec 7, 2015 at 7:50 PM, Brian Gerst <brge...@gmail.com> wrote:
> On Mon, Dec 7, 2015 at 4:51 PM, Andy Lutomirski <l...@kernel.org> wrote:
>> 64-bit syscalls currently have an optimization in which they are
>> called with partial pt_regs. A small handful require full pt_regs.
>>
>> In the 32-bit and compat cases, I cleaned this up by forcing full
>> pt_regs for all syscalls. The performance hit doesn't really matter.
>>
>> I want to clean up the 64-bit case as well, but I don't want to hurt
>> fast path performance. To do that, I want to force the syscalls
>> that use pt_regs onto the slow path. This will enable us to make
>> slow path syscalls be real ABI-compliant C functions.
>>
>> Use the new syscall entry qualification machinery for this.
>> stub_clone is now stub_clone/ptregs.
>>
>> The next patch will eliminate the stubs, and we'll just have
>> sys_clone/ptregs.
[Resend after gmail web interface fail]
I've got an idea on how to do this without the duplicate syscall table.
ptregs_foo:
leaq sys_foo(%rip), %rax
jmp stub_ptregs_64
stub_ptregs_64:
testl $TS_EXTRAREGS, <current->ti_status>
jnz 1f
SAVE_EXTRA_REGS
call *%rax
RESTORE_EXTRA_REGS
ret
1:
call *%rax
ret
This makes sure that the extra regs don't get saved a second time if
coming in from the slow path, but preserves the fast path if not
tracing.
--
Brian Gerst
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