This probe emulates a write error; a broken pipe in this case. It demonstrates setting errno and returning -1 from write().

Main test: main.c

-----------------

#include <errno.h>

#include <string.h>

int main()

{

  if( printf( "Hello World\n" ) < 1 )

  {

    /* printf failed - print error to stderr */

    fprintf( stderr, "printf failed: %s\n", strerror( errno ));

  }

  return 0;

}

The probe: write.apc

--------------------

#include <errno.h>

probe thread

{

  probe extern:"write()" in "libc.so"

  {

    int stub_flag = 0;

    on_entry

    {

      int fd = $1;

      void *buf = (void*)$2;

      size_t count = $3;

      log( "--- write(", fd, ", ", buf, ", ", count, ")" );

      if ( fd == 1 )

      {

        /* only stdout */

        stub_flag = 1;

        ap_StubRoutine;

      }

    }

    on_exit

    {

      if ( stub_flag )

      {

        errno = EPIPE;

        $return = -1;

        stub_flag = 0;

      }

    }

  }

}

The result:

----------

>aprobe -u write main

printf failed: Broken pipe

>apformat main

--- write(1, 0xbfffbac0, 12)

--- write(2, 0xbfffbac0, 27)