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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 8:19 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).
>
> About the patch, based on current timeframe I think your solution is
> the safest one for x86.
>
> 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.
--
H.J.