[PATCH, gdbserver] Further cleanup of FDPIC/DSBT divergences

[Luis Machado <lgustavo at codesourcery dot com>]

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

2013-06-20  Luis Machado  <lgustavo@codesourcery.com>

	* linux-low.c: Remove check for PT_GETDSBT.
	(target_loadmap): Remove data structure conditionalized by
	the presence of PT_GETDSBT.
	(LINUX_LOADMAP, LINUX_LOADMAP_EXEC,
	LINUX_LOADMAP_INTERP): Remove definitions.
	(linux_read_loadmap): Replace LINUX_LOADMAP_EXEC with
	PTRACE_GETFDPIC_EXEC, LINUX_LOADMAP_INTERP with
	PTRACE_GETFDPIC_INTERP and LINUX_LOADMAP with PTRACE_GETFDPIC.
	Do not set linux_read_loadmap to NULL in the absence of
	PTRACE_GETFDPIC.
	(linux_target_ops) <read_loadmap>: Only set to linux_read_loadmap
	in the presence of PTRACE_GETFDPIC.

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index bb7298a..df53775 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -5263,7 +5263,7 @@ linux_qxfer_spu (const char *annex, unsigned char *readbuf,
   return ret;
 }
 
-#if defined PT_GETDSBT || defined PTRACE_GETFDPIC
+#if defined PTRACE_GETFDPIC
 struct target_loadseg
 {
   /* Core address to which the segment is mapped.  */
@@ -5274,23 +5274,6 @@ struct target_loadseg
   Elf32_Word p_memsz;
 };
 
-# if defined PT_GETDSBT
-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*/];
-};
-#  define LINUX_LOADMAP		PT_GETDSBT
-#  define LINUX_LOADMAP_EXEC	PTRACE_GETDSBT_EXEC
-#  define LINUX_LOADMAP_INTERP	PTRACE_GETDSBT_INTERP
-# else
 struct target_loadmap
 {
   /* Protocol version number, must be zero.  */
@@ -5300,10 +5283,6 @@ struct target_loadmap
   /* The actual memory map.  */
   struct target_loadseg segs[/*nsegs*/];
 };
-#  define LINUX_LOADMAP		PTRACE_GETFDPIC
-#  define LINUX_LOADMAP_EXEC	PTRACE_GETFDPIC_EXEC
-#  define LINUX_LOADMAP_INTERP	PTRACE_GETFDPIC_INTERP
-# endif
 
 static int
 linux_read_loadmap (const char *annex, CORE_ADDR offset,
@@ -5315,13 +5294,13 @@ linux_read_loadmap (const char *annex, CORE_ADDR offset,
   unsigned int actual_length, copy_length;
 
   if (strcmp (annex, "exec") == 0)
-    addr = (int) LINUX_LOADMAP_EXEC;
+    addr = (int) PTRACE_GETFDPIC_EXEC;
   else if (strcmp (annex, "interp") == 0)
-    addr = (int) LINUX_LOADMAP_INTERP;
+    addr = (int) PTRACE_GETFDPIC_INTERP;
   else
     return -1;
 
-  if (ptrace (LINUX_LOADMAP, pid, addr, &data) != 0)
+  if (ptrace (PTRACE_GETFDPIC, pid, addr, &data) != 0)
     return -1;
 
   if (data == NULL)
@@ -5337,9 +5316,7 @@ linux_read_loadmap (const char *annex, CORE_ADDR offset,
   memcpy (myaddr, (char *) data + offset, copy_length);
   return copy_length;
 }
-#else
-# define linux_read_loadmap NULL
-#endif /* defined PT_GETDSBT || defined PTRACE_GETFDPIC */
+#endif /* defined PTRACE_GETFDPIC */
 
 static void
 linux_process_qsupported (const char *query)
@@ -6037,7 +6014,11 @@ static struct target_ops linux_target_ops = {
   NULL,
 #endif
   linux_common_core_of_thread,
+#if defined PTRACE_GETFDPIC
   linux_read_loadmap,
+#else
+  NULL,
+#endif /* defined PTRACE_GETFDPIC */
   linux_process_qsupported,
   linux_supports_tracepoints,
   linux_read_pc,