Segment register reading on Windows targets.

This patch makes sure that the value of segment registers are
read properly as 16bit values on Windows.

gdb/ChangeLog:

        * windows-nat.h (segment_register_p_ftype): New typedef.
        (windows_set_segment_register_p): Add declaration.
        * windows-nat.c (segment_register_p): New static global.
        (windows_set_segment_register_p): New function.
        (do_windows_fetch_inferior_registers): Add special handling
        for segment registers.
        * amd64-windows-nat.c: #include "amd64-tdep.h".
        (amd64_windows_segment_register_p): New function.
        (_initialize_amd64_windows_nat): Call windows_set_segment_register_p.
        * i386-windows-nat.c: #include "i386-tdep.h".
        (i386_windows_segment_register_p): New function.
        (_initialize_i386_windows_nat): Call windows_set_segment_register_p.

5 files changed, 64 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index a073454..5e63549 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,18 @@
+2012-05-04  Joel Brobecker  <brobecker@adacore.com>
+
+	* windows-nat.h (segment_register_p_ftype): New typedef.
+	(windows_set_segment_register_p): Add declaration.
+	* windows-nat.c (segment_register_p): New static global.
+	(windows_set_segment_register_p): New function.
+	(do_windows_fetch_inferior_registers): Add special handling
+	for segment registers.
+	* amd64-windows-nat.c: #include "amd64-tdep.h".
+	(amd64_windows_segment_register_p): New function.
+	(_initialize_amd64_windows_nat): Call windows_set_segment_register_p.
+	* i386-windows-nat.c: #include "i386-tdep.h".
+	(i386_windows_segment_register_p): New function.
+	(_initialize_i386_windows_nat): Call windows_set_segment_register_p.
+
 2012-05-04  Tristan Gingold  <gingold@adacore.com>
 
 	* printcmd.c (set_command): Emit a warning if the expression is not
diff --git a/gdb/amd64-windows-nat.c b/gdb/amd64-windows-nat.c
index bc2c047..e5fb0e0 100644
--- a/gdb/amd64-windows-nat.c
+++ b/gdb/amd64-windows-nat.c
@@ -18,6 +18,8 @@
 #include "defs.h"
 #include "windows-nat.h"
 #include "i386-nat.h"
+#include "amd64-tdep.h"
+
 #include <windows.h>
 
 #define context_offset(x) (offsetof (CONTEXT, x))
@@ -85,6 +87,14 @@ static const int mappings[] =
 };
 #undef context_offset
 
+/* segment_register_p_ftype implementation for amd64.  */
+
+static int
+amd64_windows_segment_register_p (int regnum)
+{
+  return regnum >= AMD64_CS_REGNUM && regnum <= AMD64_GS_REGNUM;
+}
+
 /* -Wmissing-prototypes */
 extern initialize_file_ftype _initialize_amd64_windows_nat;
 
@@ -92,5 +102,6 @@ void
 _initialize_amd64_windows_nat (void)
 {
   windows_set_context_register_offsets (mappings);
+  windows_set_segment_register_p (amd64_windows_segment_register_p);
   i386_set_debug_register_length (8);
 }
diff --git a/gdb/i386-windows-nat.c b/gdb/i386-windows-nat.c
index 5d93915..0928c9f 100644
--- a/gdb/i386-windows-nat.c
+++ b/gdb/i386-windows-nat.c
@@ -18,6 +18,7 @@
 #include "defs.h"
 #include "windows-nat.h"
 #include "i386-nat.h"
+#include "i386-tdep.h"
 
 #include <windows.h>
 
@@ -70,6 +71,14 @@ static const int mappings[] =
 };
 #undef context_offset
 
+/* segment_register_p_ftype implementation for x86.  */
+
+static int
+i386_windows_segment_register_p (int regnum)
+{
+  return regnum >= I386_CS_REGNUM && regnum <= I386_GS_REGNUM;
+}
+
 /* -Wmissing-prototypes */
 extern initialize_file_ftype _initialize_i386_windows_nat;
 
@@ -77,5 +86,6 @@ void
 _initialize_i386_windows_nat (void)
 {
   windows_set_context_register_offsets (mappings);
+  windows_set_segment_register_p (i386_windows_segment_register_p);
   i386_set_debug_register_length (4);
 }
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index f536ed1..000c86f 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -243,6 +243,10 @@ static int useshell = 0;		/* use shell for subprocesses */
 
 static const int *mappings;
 
+/* The function to use in order to determine whether a register is
+   a segment register or not.  */
+static segment_register_p_ftype *segment_register_p;
+
 /* This vector maps the target's idea of an exception (extracted
    from the DEBUG_EVENT structure) to GDB's idea.  */
 
@@ -272,6 +276,14 @@ windows_set_context_register_offsets (const int *offsets)
   mappings = offsets;
 }
 
+/* See windows-nat.h.  */
+
+void
+windows_set_segment_register_p (segment_register_p_ftype *fun)
+{
+  segment_register_p = fun;
+}
+
 static void
 check (BOOL ok, const char *file, int line)
 {
@@ -456,6 +468,14 @@ do_windows_fetch_inferior_registers (struct regcache *regcache, int r)
       l = (*((long *) context_offset) >> 16) & ((1 << 11) - 1);
       regcache_raw_supply (regcache, r, (char *) &l);
     }
+  else if (segment_register_p (r))
+    {
+      /* GDB treats segment registers as 32bit registers, but they are
+	 in fact only 16 bits long.  Make sure we do not read extra
+	 bits from our source buffer.  */
+      l = *((long *) context_offset) & 0xffff;
+      regcache_raw_supply (regcache, r, (char *) &l);
+    }
   else if (r >= 0)
     regcache_raw_supply (regcache, r, context_offset);
   else
diff --git a/gdb/windows-nat.h b/gdb/windows-nat.h
index 08200b9..a6cc5ec 100644
--- a/gdb/windows-nat.h
+++ b/gdb/windows-nat.h
@@ -20,5 +20,13 @@
 
 extern void windows_set_context_register_offsets (const int *offsets);
 
+/* A pointer to a function that should return non-zero iff REGNUM
+   corresponds to one of the segment registers.  */
+typedef int (segment_register_p_ftype) (int regnum);
+
+/* Set the function that should be used by this module to determine
+   whether a given register is a segment register or not.  */
+extern void windows_set_segment_register_p (segment_register_p_ftype *fun);
+
 #endif