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Re: [PATCH] x86-64: Add p{read,write}[v]64 to syscalls.list [BZ #20348]
On Tue, Jul 12, 2016 at 8:49 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Jul 12, 2016 at 8:19 AM, Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
>>
>>
>> On 12/07/2016 16:03, H.J. Lu wrote:
>>> On Tue, Jul 12, 2016 at 7:04 AM, Adhemerval Zanella
>>> <adhemerval.zanella@linaro.org> wrote:
>>>>
>>>>
>>>> On 12/07/2016 14:26, H.J. Lu wrote:
>>>>> 64-bit off_t in pread64, preadv, pwrite64 and pwritev syscalls is pased
>>>>> in one 64-bit register for both x32 and x86-64. Since the inline
>>>>> asm statement only passes long, which is 32-bit for x32, in registers,
>>>>> 64-bit off_t is truncated to 32-bit on x32. Since __ASSUME_PREADV and
>>>>> __ASSUME_PWRITEV are defined unconditionally, these syscalls can be
>>>>> implemented in syscalls.list to pass 64-bit off_t in one 64-bit register.
>>>>>
>>>>> Tested on x86-64 and x32 with off_t > 4GB on pread64/pwrite64 and
>>>>> preadv64/pwritev64.
>>>>>
>>>>> OK for master?
>>>>>
>>>>> H.J.
>>>>> ---
>>>>> [BZ #20348]
>>>>> * sysdeps/unix/sysv/linux/x86_64/syscalls.list: Add pread64,
>>>>> preadv64, pwrite64 and pwritev64.
>>>>> ---
>>>>> sysdeps/unix/sysv/linux/x86_64/syscalls.list | 4 ++++
>>>>> 1 file changed, 4 insertions(+)
>>>>>
>>>>> diff --git a/sysdeps/unix/sysv/linux/x86_64/syscalls.list b/sysdeps/unix/sysv/linux/x86_64/syscalls.list
>>>>> index d09d101..bcf6370 100644
>>>>> --- a/sysdeps/unix/sysv/linux/x86_64/syscalls.list
>>>>> +++ b/sysdeps/unix/sysv/linux/x86_64/syscalls.list
>>>>> @@ -6,6 +6,10 @@ msgctl - msgctl i:iip __msgctl msgctl
>>>>> msgget - msgget i:ii __msgget msgget
>>>>> msgrcv - msgrcv Ci:ibnii __msgrcv msgrcv
>>>>> msgsnd - msgsnd Ci:ibni __msgsnd msgsnd
>>>>> +pread64 - pread64 Ci:ipii __libc_pread __libc_pread64 __pread64 pread64 __pread pread
>>>>> +preadv64 - preadv Ci:ipii preadv64 preadv
>>>>> +pwrite64 - pwrite64 Ci:ipii __libc_pwrite __pwrite64 pwrite64 __pwrite pwrite
>>>>> +pwritev64 - pwritev Ci:ipii pwritev64 pwritev
>>>>> shmat - shmat i:ipi __shmat shmat
>>>>> shmctl - shmctl i:iip __shmctl shmctl
>>>>> shmdt - shmdt i:s __shmdt shmdt
>>>>>
>>>>
>>>> This is pretty much what I suggested [1] with the difference that my
>>>> idea is to re-add the auto-generated wrappers just for x32. I would
>>>> prefer to keep x86_64 continue to use default implementation and
>>>> work on fix {INLINE,INTERNAL}_SYSCALL to work with 64-bit arguments
>>>> in x32.
>>>
>>> syscalls.list is the preferred way to implement a system call, not
>>> {INLINE,INTERNAL}_SYSCALL. There is no reason only to do it
>>> for x32. As for {INLINE,INTERNAL}_SYSCALL with 64-bit argument,
>>> they are only used in p{read,write}[v]64 and it is incorrect to pass long
>>> as 64-bit integer to x32 syscall if the argument is long or pointer.
>>
>> The idea I am trying to push with all these consolidation are twofold:
>>
>> 1. Remove the complexity implementation files and way to call syscalls
>> inside GLIBC and make easier to implement new ports
>
> That is fine.
>
>> 2. Remove the redundant sysdep-cancel.h requirement for each port
>> which basically implementations pic/nopic function calls in assembly.
>> This is also remove implementation complexity and make easier for
>> new port implementation.
>>
>> Also, for 2. it also helps the long standing pthread cancellation
>> (bz#12683) by focusing all cancellation calls in only one implementation.
>>
>> I do get the idea the auto-generation call is currently preferred way
>> to implementation syscalls, but I think for *cancellable* way we should
>> push to implement using SYSCALL_CANCEL (which is in turn based on
>> INTERNAL_SYSCALL).
>
> That is fine also. But on x86-64, we should use syscalls.list if possible,
> especially for cancellation calls.
>
> With {INLINE,INTERNAL}_SYSCALL:
>
> 0000000000000000 <__libc_pread>:
> 0: 8b 05 00 00 00 00 mov 0x0(%rip),%eax # 6 <__libc_pread+0x6>
> 6: 49 89 ca mov %rcx,%r10
> 9: 85 c0 test %eax,%eax
> b: 75 2b jne 38 <__libc_pread+0x38>
> d: 48 63 ff movslq %edi,%rdi
> 10: b8 11 00 00 00 mov $0x11,%eax
> 15: 0f 05 syscall
> 17: 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax
> 1d: 77 01 ja 20 <__libc_pread+0x20>
> 1f: c3 retq
> 20: 48 8b 15 00 00 00 00 mov 0x0(%rip),%rdx # 27 <__libc_pread+0x27>
> 27: f7 d8 neg %eax
> 29: 64 89 02 mov %eax,%fs:(%rdx)
> 2c: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
> 33: c3 retq
> 34: 0f 1f 40 00 nopl 0x0(%rax)
> 38: 41 55 push %r13
> 3a: 41 54 push %r12
> 3c: 49 89 cd mov %rcx,%r13
> 3f: 55 push %rbp
> 40: 53 push %rbx
> 41: 49 89 d4 mov %rdx,%r12
> 44: 48 89 f5 mov %rsi,%rbp
> 47: 89 fb mov %edi,%ebx
> 49: 48 83 ec 18 sub $0x18,%rsp
> 4d: e8 00 00 00 00 callq 52 <__libc_pread+0x52>
> 52: 4d 89 ea mov %r13,%r10
> 55: 41 89 c0 mov %eax,%r8d
> 58: 4c 89 e2 mov %r12,%rdx
> 5b: 48 89 ee mov %rbp,%rsi
> 5e: 48 63 fb movslq %ebx,%rdi
> 61: b8 11 00 00 00 mov $0x11,%eax
> 66: 0f 05 syscall
> 68: 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax
> 6e: 77 1d ja 8d <__libc_pread+0x8d>
> 70: 44 89 c7 mov %r8d,%edi
> 73: 48 89 44 24 08 mov %rax,0x8(%rsp)
> 78: e8 00 00 00 00 callq 7d <__libc_pread+0x7d>
> 7d: 48 8b 44 24 08 mov 0x8(%rsp),%rax
> 82: 48 83 c4 18 add $0x18,%rsp
> 86: 5b pop %rbx
> 87: 5d pop %rbp
> 88: 41 5c pop %r12
> 8a: 41 5d pop %r13
> 8c: c3 retq
> 8d: 48 8b 15 00 00 00 00 mov 0x0(%rip),%rdx # 94 <__libc_pread+0x94>
> 94: f7 d8 neg %eax
> 96: 64 89 02 mov %eax,%fs:(%rdx)
> 99: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
> a0: eb ce jmp 70 <__libc_pread+0x70>
>
> With syscalls.list:
>
> Disassembly of section .text:
>
> 0000000000000000 <__libc_pread>:
> 0: 83 3d 00 00 00 00 00 cmpl $0x0,0x0(%rip) # 7 <__libc_pread+0x7>
> 7: 75 17 jne 20 <__pread64_nocancel+0x17>
>
> 0000000000000009 <__pread64_nocancel>:
> 9: 49 89 ca mov %rcx,%r10
> c: b8 11 00 00 00 mov $0x11,%eax
> 11: 0f 05 syscall
> 13: 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax
> 19: 0f 83 00 00 00 00 jae 1f <__pread64_nocancel+0x16>
> 1f: c3 retq
> 20: 48 83 ec 08 sub $0x8,%rsp
> 24: e8 00 00 00 00 callq 29 <__pread64_nocancel+0x20>
> 29: 48 89 04 24 mov %rax,(%rsp)
> 2d: 49 89 ca mov %rcx,%r10
> 30: b8 11 00 00 00 mov $0x11,%eax
> 35: 0f 05 syscall
> 37: 48 8b 3c 24 mov (%rsp),%rdi
> 3b: 48 89 c2 mov %rax,%rdx
> 3e: e8 00 00 00 00 callq 43 <__pread64_nocancel+0x3a>
> 43: 48 89 d0 mov %rdx,%rax
> 46: 48 83 c4 08 add $0x8,%rsp
> 4a: 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax
> 50: 0f 83 00 00 00 00 jae 56 <__pread64_nocancel+0x4d>
> 56: c3 retq
>
> This one is much better.
>
>>>
>>>> Also, I think we should remove the first try to fix LO_HI_LONG [2],
>>>> since 64 bits argument does not work correct in x32 anyway.
>>>
>>> I think LO_HI_LONG should be defined only if __WORDSIZE != 64
>>> and p{read,write}[v]64 should be added to wordsize-64/syscalls.list.
>>
>> Indeed this is something I will get back now that I see x32 fails
>> with current implementation. I got the wrong idea all ILP32 would
>> use the compat code (as MIPS64n64).
x86/entry/syscalls/syscall_64.tbl has
17 common pread64 sys_pread64
295 64 preadv sys_preadv
534 x32 preadv compat_sys_preadv64
compat_sys_preadv64 takes 64-bit offset in one piece.
>> About the patch, based on current timeframe I think your solution is
>> the safest one for x86.
I will check it in.
>> However I do would like to re-enable it on x86, including x32, when 2.25
>> opens. The patch below changes slight on how {INLINE,INTERNAL}_SYSCALL
>> works on x32: int/long/pointer should be passed as before and uint64_t
>> arguments should be passed as register all well without casting.
>> If you have time I would like to check if it would be acceptable for
>> 2.25. It shows no regression on x32, including the tst-preadwrite{64}
>> testcase you sent earlier:
>
> I will give it a try.
I got no regressions on x32. But on x86-64, I got
Inconsistency detected by ld.so: dl-tls.c: 493: _dl_allocate_tls_init:
Assertion `listp->slotinfo[cnt].gen <= GL(dl_tls_generation)' failed!
FAIL: nptl/tst-stack4
It doesn't fail every time. I am wondering if typeof returns the
correct type on
signed/unsigned integer constants.
--
H.J.