Re: Get the real system call wrappers

[Yubin Ruan <ablacktshirt at gmail dot com>]

2017-08-22 21:52 GMT+08:00 Adhemerval Zanella <adhemerval.zanella@linaro.org>:
>
>
> On 19/08/2017 11:34, Yubin Ruan wrote:
>> Hi,
>> How can I get the complete glibc system call wrappers?
>> I know that glibc implement most system call wrappers but they are not
>> exposed explicitly in the glibc source. Rather, the complete system
>> call wrappers are generated on the fly when glibc is built, probably
>> using some scripts. For example, the "open(2)" system call is now
>> defined in io/open.c:
>>
>>     29 __libc_open (const char *file, int oflag)
>>     30 {
>>     31  int mode;
>>     32
>>     33  if (file == NULL)
>>     34  {
>>     35  __set_errno (EINVAL);
>>     36  return -1;
>>     37  }
>>     38
>>     39  if (__OPEN_NEEDS_MODE (oflag))
>>     40  {
>>     41  va_list arg;
>>     42  va_start(arg, oflag);
>>     43  mode = va_arg(arg, int);
>>     44  va_end(arg);
>>     45  }
>>     46
>>     47  __set_errno (ENOSYS);
>>     48  return -1;
>>     49 }
>>     50 libc_hidden_def (__libc_open)
>>     51 weak_alias (__libc_open, __open)
>>     52 libc_hidden_weak (__open)
>>     53 weak_alias (__libc_open, open)
>>     54
>>     55 stub_warning (open)
>>     56
>>     57 /* __open_2 is a generic wrapper that calls __open.
>>     58  So give a stub warning for that symbol too. */
>>     59 stub_warning (__open_2)
>>
>> After some replacement (I guess), we will get a complete open(2)
>> system call wrapper.
>>
>> But all methods I found on the web to generate the complete wrappers
>> seem to be obsolete (can't find those scripts). Do I have to built the
>> whole glibc completely to obtain those? Or is there any lightweight
>> method?
>
> The syscall generation mechanism is described in this wiki entry [1],
> and although it would require some updates (which I intend to do after
> I finish my sysdep-cancel.h cleanup) it holds for current version.
>
> [1] https://sourceware.org/glibc/wiki/SyscallWrappers

Thanks. But as for the current version, the script that was used to generate
all the system call, as mentioned in [1], "sysdep/unix/make-syscalls.sh",
cannot be found any more.

I tried using a old release, but please do let me know once there are any
updates.

Thanks,
Yubin

[1] https://sourceware.org/glibc/wiki/SyscallWrappers