[RFA] gdbserver fetch/store registers problem on s390x

[Ulrich Weigand <uweigand@de.ibm.com>]

Hello,

this patch fixes another problem with gdbserver on s390x occurring
on recent kernels.  The problem is that some registers accessed by
ptrace (notably the access registers and the floating-point status
register) are still 32 bits wide, even though the PTRACE_PEEKUSER
and PTRACE_POKEUSER commands always transfer 64 bits.

This is a problem for two reasons: when fetching those registers,
a 4-byte buffer is allocated via alloca, but then 8 bytes are 
written to that buffer (which just happens to work because alloca
rounds the size up to the next multiple of 8 anyway).  The same
holds for storing the register; but in this case the second 4 bytes
have just random contents, and recent kernels won't allow the POKEUSER
command to succeed unless those extra bytes are zero.

The following patch fixes this problem by always allocating a buffer
that has multiple of sizeof (PTRACE_XFER_TYPE) as size, and by
zeroing out the excess bytes of the buffer when storing the register.

Tested on s390-ibm-linux and s390x-ibm-linux.
OK?

Bye,
Ulrich


ChangeLog:

	* linux-low.c (fetch_register): Ensure buffer size is a multiple
	of sizeof (PTRACE_XFER_TYPE).
	(usr_store_inferior_registers): Likewise.  Zero out excess bytes.

Index: gdb/gdbserver/linux-low.c
===================================================================
RCS file: /cvs/src/src/gdb/gdbserver/linux-low.c,v
retrieving revision 1.34
diff -c -p -r1.34 linux-low.c
*** gdb/gdbserver/linux-low.c	3 Mar 2005 16:56:53 -0000	1.34
--- gdb/gdbserver/linux-low.c	10 May 2005 11:53:40 -0000
*************** static void
*** 1095,1101 ****
  fetch_register (int regno)
  {
    CORE_ADDR regaddr;
!   register int i;
    char *buf;
  
    if (regno >= the_low_target.num_regs)
--- 1095,1101 ----
  fetch_register (int regno)
  {
    CORE_ADDR regaddr;
!   int i, size;
    char *buf;
  
    if (regno >= the_low_target.num_regs)
*************** fetch_register (int regno)
*** 1106,1113 ****
    regaddr = register_addr (regno);
    if (regaddr == -1)
      return;
!   buf = alloca (register_size (regno));
!   for (i = 0; i < register_size (regno); i += sizeof (PTRACE_XFER_TYPE))
      {
        errno = 0;
        *(PTRACE_XFER_TYPE *) (buf + i) =
--- 1106,1115 ----
    regaddr = register_addr (regno);
    if (regaddr == -1)
      return;
!   size = (register_size (regno) + sizeof (PTRACE_XFER_TYPE) - 1)
!          & - sizeof (PTRACE_XFER_TYPE);
!   buf = alloca (size);
!   for (i = 0; i < size; i += sizeof (PTRACE_XFER_TYPE))
      {
        errno = 0;
        *(PTRACE_XFER_TYPE *) (buf + i) =
*************** static void
*** 1147,1153 ****
  usr_store_inferior_registers (int regno)
  {
    CORE_ADDR regaddr;
!   int i;
    char *buf;
  
    if (regno >= 0)
--- 1149,1155 ----
  usr_store_inferior_registers (int regno)
  {
    CORE_ADDR regaddr;
!   int i, size;
    char *buf;
  
    if (regno >= 0)
*************** usr_store_inferior_registers (int regno)
*** 1162,1170 ****
        if (regaddr == -1)
  	return;
        errno = 0;
!       buf = alloca (register_size (regno));
        collect_register (regno, buf);
!       for (i = 0; i < register_size (regno); i += sizeof (PTRACE_XFER_TYPE))
  	{
  	  errno = 0;
  	  ptrace (PTRACE_POKEUSER, inferior_pid, (PTRACE_ARG3_TYPE) regaddr,
--- 1164,1175 ----
        if (regaddr == -1)
  	return;
        errno = 0;
!       size = (register_size (regno) + sizeof (PTRACE_XFER_TYPE) - 1)
! 	     & - sizeof (PTRACE_XFER_TYPE);
!       buf = alloca (size);
!       memset (buf, 0, size);
        collect_register (regno, buf);
!       for (i = 0; i < size; i += sizeof (PTRACE_XFER_TYPE))
  	{
  	  errno = 0;
  	  ptrace (PTRACE_POKEUSER, inferior_pid, (PTRACE_ARG3_TYPE) regaddr,
-- 
  Dr. Ulrich Weigand
  Linux on zSeries Development
  Ulrich.Weigand@de.ibm.com