cvs commit: src/sys/kern subr_sbuf.c

[Peter Wemm]

peter       2003/05/25 12:03:08 PDT

  FreeBSD src repository

  Modified files:
    sys/kern             subr_sbuf.c 
  Log:
  Copy the va_list in sbuf_vprintf() before passing it to vsnprintf(),
  because we could fail due to a small buffer and loop and rerun.  If this
  happens, then the vsnprintf() will have already taken the arguments off
  the va_list.  For i386 and others, this doesn't matter because the
  va_list type is a passed as a copy.  But on powerpc and amd64, this is
  fatal because the va_list is a reference to an external structure that
  keeps the vararg state due to the more complicated argument passing system.
  On amd64, arguments can be passed as follows:
  First 6 int/pointer type arguments go in registers, the rest go on
    the memory stack.
  Float and double are similar, except using SSE registers.
  long double (80 bit precision) are similar except using the x87 stack.
  Where the 'next argument' comes from depends on how many have been
  processed so far and what type it is.  For amd64, gcc keeps this state
  somewhere that is referenced by the va_list.
  
  I found a description that showed the va_copy was required here:
  http://mirrors.ccs.neu.edu/cgi-bin/unixhelp/man-cgi?va_end+9
  The single unix spec doesn't mention va_copy() at all.
  
  Anyway, the problem was that the sysctl kern.geom.conf* nodes would panic
  due to walking off the end of the va_arg lists in vsnprintf.  A better fix
  would be to have sbuf_vprintf() use a single pass and call kvprintf()
  with a callback function that stored the results and grew the buffer
  as needed.
  
  Approved by:    re (scottl)
  
  Revision  Changes    Path
  1.24      +4 -1      src/sys/kern/subr_sbuf.c