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Re: [PATCH] x86-64: Add p{read,write}[v]64 to syscalls.list [BZ #20348]
On 12/07/2016 17:19, H.J. Lu wrote:
> 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.
I think SYSCALL_CANCEL can be slight improved by using INTERNAL_SYSCALL
instead of INLINE_SYSCALL and checking the error outside of cancellation
handling. I see a slight improvement, however sysdep-cancel.h is
still slight better.
However the idea is I am trying to push in the end is to remove the
sysdep-cancel.h because the new cancellation scheme will require it
to basically do a function call instead of calling the cancellation
enable/disable (which will be also removed).
>>
>>>>
>>>>> 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.
>
I think the issue is not really related to this patch. I also see this
very issue in i386, powerpc64le and aarch64 in a inconsistent way
Regarding typeof type for signed/unsigned, it looks like gcc gets it
right:
$ cat test.c
#include <stdio.h>
unsigned char uc;
signed char sc;
int foo_1 ()
{
typeof (uc) c = 255;
return c > 128;
}
int foo_2 ()
{
typeof (sc) c = 255;
return c > 128;
}
int
main (void)
{
printf ("%i\n%i\n", foo_1 (), foo_2 ());
return 0;
}
$ gcc test.c
$ ./a.out
1
0