[PATCH 1/3] x86: work around compiler diagnosing dangling pointer

[Jan Beulich <jbeulich@suse.com>]

For quite come time print_insn() has been storing the address of a local
variable into info->private_data. Since the compiler can't know that the
field won't be accessed again after print_insn() returns, it may kind of
legitimately diagnose this. And recent enough gcc does as of the
introduction of the fetch_error() return paths (replacing setjmp()-based
error handling).

Utilizing that neither prefix_name() nor i386_dis_printf() actually use
info->private_data, zap the pointer in fetch_error(), after having
retrieved it for local use.
---
Let's hope that this addresses the observed issues, which I haven't been
seeing myself. And of course there are further return paths which may
(sooner or later) also have such a warning trigger.

--- a/opcodes/i386-dis.c
+++ b/opcodes/i386-dis.c
@@ -345,6 +345,12 @@ fetch_error (const instr_info *ins)
   const struct dis_private *priv = ins->info->private_data;
   const char *name = NULL;
 
+  /* Our caller has put a pointer to a local variable in info->private_data
+     and it is going to return right after this function has returned.  Some
+     compilers diagnose this as a dangling pointer.  Zap the pointer here to
+     avoid needing to do so on all involved return paths in the caller.  */
+  ins->info->private_data = NULL;
+
   if (ins->codep <= priv->the_buffer)
     return -1;