System call select on R4600

System call select on R4600

[Macleod]

 My problem is "select" system call always return -1
 and errno is -4142, but sys_select has never been called.
 Think, it has some problem on handling system call. 
 Because if I change SYS(sys_select, 5) to 4 arguments,
 sys_select will be executed. 
 Thanks!

 Compiler: gcc-3.3.3
 Kernel: mips-linux-2.4.25/mips-linux-2.4.26
 Compile parameter:
 -Wno-inline \
 -Werror-implicit-function-declarations \
 -fno-PIC \
 -fno-common \
 -mno-abicalls \
 -mlong-calls \
 -march=r4600 \
 -mtune=r4600 \
 -G 0 \
 -Wa,--trap

Re: System call select on R4600

[Ralf Baechle]

On Sun, Aug 22, 2004 at 11:54:10AM +0800, Macleod wrote:

>  My problem is "select" system call always return -1
>  and errno is -4142, but sys_select has never been called.
>  Think, it has some problem on handling system call. 
>  Because if I change SYS(sys_select, 5) to 4 arguments,
>  sys_select will be executed. 
>  Thanks!

This is a bug which was fixed a while ago.  I assume your application
is picking up a bad definition from an old kernel header package or so.
Still doing syscalls directly is a fragily; better avoid and use your
libc's select(3).

  Ralf

Re: System call select on R4600

[Macleod]

 After trace system, found this problem is from scall_o32.S
 line 161 in 2.4.26 kernel.

 bltz t0, bad_stack   # -> sp is bad

 If stack address larger than 0x7fffffff, branch will take, 
 and that's why I got "-4142" errno on select system call
 even parameters in stack are correct. I tried to remove this
 line and seems "select" works fine.


-----Original message-----
From:Ralf Baechle <ralf@linux-mips.org>
To:Macleod <macleod@mail2000.com.tw>
Cc:linux-mips@linux-mips.org
Date:Sun, 22 Aug 2004 14:14:36 +0200
Subject:Re: System call select on R4600

On Sun, Aug 22, 2004 at 11:54:10AM +0800, Macleod wrote:

>  My problem is "select" system call always return -1
>  and errno is -4142, but sys_select has never been called.
>  Think, it has some problem on handling system call. 
>  Because if I change SYS(sys_select, 5) to 4 arguments,
>  sys_select will be executed. 
>  Thanks!

This is a bug which was fixed a while ago.  I assume your application
is picking up a bad definition from an old kernel header package or so.
Still doing syscalls directly is a fragily; better avoid and use your
libc's select(3).

  Ralf

Re: System call select on R4600

[Ralf Baechle]

On Wed, Aug 25, 2004 at 10:18:04AM +0800, Macleod wrote:

>  After trace system, found this problem is from scall_o32.S
>  line 161 in 2.4.26 kernel.
> 
>  bltz t0, bad_stack   # -> sp is bad
> 
>  If stack address larger than 0x7fffffff, branch will take, 
>  and that's why I got "-4142" errno on select system call
>  even parameters in stack are correct. I tried to remove this
>  line and seems "select" works fine.

Oh yes, I forgot on this one :-)  It's intentional; making all syscalls
work from kernel mode would add some overhead.  Possible solutions:

 - move to 64-bit kernels; the 64-bit syscall interface happens to support
   upto 8 arguments for syscalls from kernel mode.
 - move your module or parts of it to userspace.  Something that's using
   select suspiciously looks like something that shouldn't be in the kernel.
 - use the proper kernel APIs.  Kernel programming isn't user space
   programming.

  Ralf