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SubjectRe: [PATCH v2 3/7] Introduce a new clone4 syscall with more flag bits and extensible arguments
On Mon, Mar 23, 2015 at 3:05 PM,  <josh@joshtriplett.org> wrote:
> On Mon, Mar 23, 2015 at 02:11:45PM +0000, David Drysdale wrote:
>> On Sun, Mar 15, 2015 at 7:59 AM, Josh Triplett <josh@joshtriplett.org> wrote:
>> > diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
>> > index 0286735..ba28306 100644
>> > --- a/arch/x86/ia32/ia32entry.S
>> > +++ b/arch/x86/ia32/ia32entry.S
>> > @@ -483,6 +483,7 @@ GLOBAL(\label)
>> > PTREGSCALL stub32_execveat, compat_sys_execveat
>> > PTREGSCALL stub32_fork, sys_fork
>> > PTREGSCALL stub32_vfork, sys_vfork
>> > + PTREGSCALL stub32_clone4, compat_sys_clone4
>> >
>> > ALIGN
>> > GLOBAL(stub32_clone)
>> > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
>> > index 1d74d16..ead143f 100644
>> > --- a/arch/x86/kernel/entry_64.S
>> > +++ b/arch/x86/kernel/entry_64.S
>> > @@ -520,6 +520,7 @@ END(\label)
>> > FORK_LIKE clone
>> > FORK_LIKE fork
>> > FORK_LIKE vfork
>> > + FORK_LIKE clone4
>> > FIXED_FRAME stub_iopl, sys_iopl
>> >
>> > ENTRY(stub_execve)
>> > diff --git a/arch/x86/syscalls/syscall_32.tbl b/arch/x86/syscalls/syscall_32.tbl
>> > index b3560ec..56fcc90 100644
>> > --- a/arch/x86/syscalls/syscall_32.tbl
>> > +++ b/arch/x86/syscalls/syscall_32.tbl
>> > @@ -365,3 +365,4 @@
>> > 356 i386 memfd_create sys_memfd_create
>> > 357 i386 bpf sys_bpf
>> > 358 i386 execveat sys_execveat stub32_execveat
>> > +359 i386 clone4 sys_clone4 stub32_clone4
>> > diff --git a/arch/x86/syscalls/syscall_64.tbl b/arch/x86/syscalls/syscall_64.tbl
>> > index 8d656fb..af15b0f 100644
>> > --- a/arch/x86/syscalls/syscall_64.tbl
>> > +++ b/arch/x86/syscalls/syscall_64.tbl
>> > @@ -329,6 +329,7 @@
>> > 320 common kexec_file_load sys_kexec_file_load
>> > 321 common bpf sys_bpf
>> > 322 64 execveat stub_execveat
>> > +323 64 clone4 stub_clone4
>> >
>> > #
>> > # x32-specific system call numbers start at 512 to avoid cache impact
>> > @@ -368,3 +369,4 @@
>> > 543 x32 io_setup compat_sys_io_setup
>> > 544 x32 io_submit compat_sys_io_submit
>> > 545 x32 execveat stub_x32_execveat
>> > +546 x32 clone4 stub32_clone4
>>
>> Doesn't this need an x32 specific wrapper (to ensure the full
>> set of registers are saved)?
>
> I'm not an x32 expert; I don't know how x32 interacts with pt_regs and
> compat syscalls. Could an x32 expert weigh in, please?
>
> - Josh Triplett

(In the absence of an x32 expert chiming in...)

As I understand it:
- stub32_clone4 expects 32-bit calling conventions and calls compat_sys_clone4
- stub_clone4 expects 64-bit calling conventions and calls sys_clone4
- stub_x32_clone4 would expect 64-bit calling conventions but call
compat_sys_clone4.

Also, I have a suspicion that different field types in the [compat_]clone4_args
structure may cause problems -- I *think* its (final) layout will be 4+4+4+4+4+4
on 32-bit, 8+8+8+8+8+4 on 64-bit, but 4+4+8+8+4+4 on x32.

Have you tried running a test with a userspace program compiled with -mx32?


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