On Tue, Jun 9, 2015 at 12:18 PM, Denys Vlasenko <dvlas...@redhat.com> wrote: > On 06/09/2015 09:11 PM, Andy Lutomirski wrote: >> On Tue, Jun 9, 2015 at 12:03 PM, Denys Vlasenko <dvlas...@redhat.com> wrote: >>> On 06/09/2015 09:01 PM, Andy Lutomirski wrote: >>>> On Tue, Jun 9, 2015 at 11:54 AM, Denys Vlasenko <dvlas...@redhat.com> >>>> wrote: >>>>> This doesn't change much, but this uses shorter 32-bit insns: >>>>> >>>>> -48 8b 74 24 68 mov 0x68(%rsp),%rsi >>>>> -48 8b 7c 24 70 mov 0x70(%rsp),%rdi >>>>> -48 8b 54 24 60 mov 0x60(%rsp),%rdx >>>>> +8b 74 24 68 mov 0x68(%rsp),%esi >>>>> +8b 7c 24 70 mov 0x70(%rsp),%edi >>>>> +8b 54 24 60 mov 0x60(%rsp),%edx >>>>> >>>>> Since these are the only uses of RESTORE_RSI_RDI[_RDX], drop these macros. >>>>> >>>> >>>> It probably doesn't matter for these fast paths, but, for the full >>>> slow path return, we really do need to restore the full pt_regs. >>>> After all, the syscall we're returning from might be sigreturn. >>> >>> This is compat 32-bit syscall handling code. >>> IIUC we do not restore high half of any registers for 32-bit tasks. >>> >>> Am I missing something? >> >> Yes -- 64-bit tasks can call 32-bit compat syscalls. > > Not via SYSCALL and SYSENTER code paths. This patch touches only those > code paths.
I suppose that's true enough even if it's not quite true. A 64-bit task could far jump/call/return to compat mode and then do SYSCALL or SYSENTER, but it will likely crash and burn because there's no 32-bit vdso. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
