gdb: fix possible uninitialised variable use

After this commit:

  commit 198ff6ff819c240545f9fc68b39636fd376d4ba9
  Date:   Tue Jan 30 15:37:23 2024 +0000

      gdb/gdbserver: share x86/linux tdesc caching

a possible use of an uninitialised variable was introduced, the
'tdesc' variable in i386_linux_core_read_description might be read
without being written too if 'xcr0' was 0.

This is fixed in this commit.  I've updated the function to follow the
same pattern as amd64_linux_core_read_description, if xcr0 is 0 then
we select a default xcr0 value and use that to select a tdesc.

diff --git a/gdb/i386-linux-tdep.c b/gdb/i386-linux-tdep.c
index ed1442236e8e23e6dd8abc154c81a42bf70e5e96..2e84384306d774ea04a69d63b13718b281e34dbd 100644 (file)
--- a/gdb/i386-linux-tdep.c
+++ b/gdb/i386-linux-tdep.c
@@ -700,17 +700,15 @@ i386_linux_core_read_description (struct gdbarch *gdbarch,
   x86_xsave_layout layout;
   uint64_t xcr0 = i386_linux_core_read_xsave_info (abfd, layout);
 
-  const struct target_desc *tdesc;
-  if (xcr0 != 0)
-    tdesc = i386_linux_read_description (xcr0);
-
-  if (tdesc != NULL)
-    return tdesc;
+  if (xcr0 == 0)
+    {
+      if (bfd_get_section_by_name (abfd, ".reg-xfp") != nullptr)
+       xcr0 = X86_XSTATE_SSE_MASK;
+      else
+       xcr0 = X86_XSTATE_X87_MASK;
+    }
 
-  if (bfd_get_section_by_name (abfd, ".reg-xfp") != NULL)
-    return i386_linux_read_description (X86_XSTATE_SSE_MASK);
-  else
-    return i386_linux_read_description (X86_XSTATE_X87_MASK);
+  return i386_linux_read_description (xcr0);
 }
 
 /* Similar to i386_supply_fpregset, but use XSAVE extended state.  */