[PATCH 1/2] GDBserver: qXfer:libraries-svr4:read, and big endian hosts

[Pedro Alves <palves at redhat dot com>]

read_one_ptr doesn't work correctly on big endian machines, in the
case of a 64-bit GDBserver debugging a 32-bit inferior, which means
read_one_ptr is given a PTR_SIZE which is narrower than the size of
CORE_ADDR.  With patch #2 applied before this patch, GDBserver would
fail to walk the DSO list correctly (e.g., the lm_next pointer would
be misread with a 32-bit shift), and GDBserver would end up always
sending an empty DSO list to GDB.

This patch fixes it.

--
Pedro Alves

2012-03-23  Pedro Alves  <palves@redhat.com>

	* linux-low.c (read_one_ptr): Read the inferior's pointer through
	a variable whose type size is the same as the inferior's pointer
	size.
---
 0 files changed, 0 insertions(+), 0 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 4734f15..2dc903d 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -5428,8 +5428,30 @@ get_r_debug (const int pid, const int is_elf64)
 static int
 read_one_ptr (CORE_ADDR memaddr, CORE_ADDR *ptr, int ptr_size)
 {
-  *ptr = 0;
-  return linux_read_memory (memaddr, (unsigned char *) ptr, ptr_size);
+  int ret;
+
+  /* Go through a union so this works on either big or little endian
+     hosts, when the inferior's pointer size is smaller than the size
+     of CORE_ADDR.  It is assumed the inferior's endianness is the
+     same of the superior's.  */
+  union
+  {
+    CORE_ADDR core_addr;
+    unsigned int ui;
+    unsigned char uc;
+  } addr;
+
+  ret = linux_read_memory (memaddr, &addr.uc, ptr_size);
+  if (ret == 0)
+    {
+      if (ptr_size == sizeof (CORE_ADDR))
+	*ptr = addr.core_addr;
+      else if (ptr_size == sizeof (unsigned int))
+	*ptr = addr.ui;
+      else
+	gdb_assert_not_reached ("unhandled pointer size");
+    }
+  return ret;
 }
 
 struct link_map_offsets