Hi,

At some point, c6x used different data structures for its DSBT-based 
loadmap.

DSBT-based

struct target_loadmap
{
   /* Protocol version number, must be zero.  */
   Elf32_Word version;
   /* Pointer to the DSBT table, its size, and the DSBT index.  */
   unsigned *dsbt_table;
   unsigned dsbt_size, dsbt_index;
   /* Number of segments in this map.  */
   Elf32_Word nsegs;
   /* The actual memory map.  */
   struct target_loadseg segs[/*nsegs*/];
};

FDPIC-based

struct target_loadmap
{
   /* Protocol version number, must be zero.  */
   Elf32_Half version;
   /* Number of segments in this map.  */
   Elf32_Half nsegs;
   /* The actual memory map.  */
   struct target_loadseg segs[/*nsegs*/];
};

We shared a little bit of code with FDPIC-based targets though...

struct target_loadseg
{
   /* Core address to which the segment is mapped.  */
   Elf32_Addr addr;
   /* VMA recorded in the program header.  */
   Elf32_Addr p_vaddr;
   /* Size of this segment in memory.  */
   Elf32_Word p_memsz;
};

Things have changed, and c6x is now using the exact same data structures 
as FDPIC-based targets in uClibc. Please refer to 
http://lists.uclibc.org/pipermail/uclibc/2013-May/047789.html for the 
uClibc changes that led to this.

Mark Salter, the author of the uClibc change, has agreed with the 
solution i proposed: 
http://lists.uclibc.org/pipermail/uclibc/2013-May/047790.html.

It is all good, but we've been conditionalizing the c6x-specific 
target_loadmap data structure based on the presence of PT_GETDSBT. This 
has always been defined in uClibc and, since Mark's change, it doesn't 
work as a hint of whether to use the new or the old target_loadmap data 
structure anymore. Therefore we will/already have a potential problem 
with backwards compatibility.

Bernhard has stated that backwards compatibility on uClibc's side is not 
a problem: http://lists.uclibc.org/pipermail/uclibc/2013-June/047801.html.

With all that exposed, my proposed change to gdbserver is to drop all 
the DSBT-specific bits, remove their definitions and explicitly use 
FDPIC definitions instead, making things a little bit cleaner.

In the following patch i also changed the code slightly to stop defining 
linux_read_loadmap to NULL and i switched to explicitly setting the 
target hook to NULL in the absence of the required definition.

What do you think? Yao? Mike?

Luis