Re: RFA: probable rs6000-aix-tdep.c bug found by clang

[Joel Brobecker <brobecker@adacore.com>]

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> OK - I will take care of removing the condition and simplifying
> the function.

Here is what I propose we check in.  I can't test it at the moment,
because we've suffered a massive power outage and we're still working
on getting every machine back up. I'm fairly confident, though.

Rather than remove the check, I added an assertion. That's because
eventually I want to add an extra check, for Lynx178. On the GDB side,
the Lynx178 port is roughly a bareboard powerpc configuration. But
it is using XCOFF, and I wanted to make sure that we'd never match
a Lynx178 binary with the AIX ABI. To do that, I use a BFD/XCOFF
function, so I thought adding the explict assertion would help.

While at it, I added a function description, that explicitly mentions
the pre-condition/assertion.

If there are no objections, I will commit the attached patch within
the next few days, after being able to test on AIX again.

Thanks,
-- 
Joel

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From a2aff2ac36f9573ede236e899994054e6194ba65 Mon Sep 17 00:00:00 2001
From: Joel Brobecker <brobecker@adacore.com>
Date: Thu, 18 Oct 2012 11:31:28 -0700
Subject: [PATCH] ppc-aix osabi sniffer: Turn test of bfd flavour into
 assertion

Due to the way this function is registers, we know that given bfd's
flavour should always be bfd_target_xcoff_flavour, thus making
the former test always true, which means that this function should
always return GDB_OSABI_AIX, and never return GDB_OSABI_UNKNOWN.

This patch also fixes a typo detected by Tom Tromey that caused
the test itself to be completely ineffective.

gdb/ChangeLog (by Tom Tromey and Joel Brobecker):

        * rs6000-aix-tdep.c (rs6000_aix_osabi_sniffer): Replace
        inneffective if condition by gdb assertion.  Add function
        description comment.
---
 gdb/rs6000-aix-tdep.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/gdb/rs6000-aix-tdep.c b/gdb/rs6000-aix-tdep.c
index 59cfa73..06b43de 100644
--- a/gdb/rs6000-aix-tdep.c
+++ b/gdb/rs6000-aix-tdep.c
@@ -719,14 +719,19 @@ rs6000_software_single_step (struct frame_info *frame)
   return 1;
 }
 
+/* Implement an osabi sniffer for RS6000/AIX.
+
+   This function assumes that ABFD's flavour is XCOFF.  In other words,
+   it should be registered as a sniffer for bfd_target_xcoff_flavour
+   objfiles only.  A failed assertion will be raised if this condition
+   is not met.  */
+
 static enum gdb_osabi
 rs6000_aix_osabi_sniffer (bfd *abfd)
 {
-  
-  if (bfd_get_flavour (abfd) == bfd_target_xcoff_flavour);
-    return GDB_OSABI_AIX;
+  gdb_assert (bfd_get_flavour (abfd) == bfd_target_xcoff_flavour);
 
-  return GDB_OSABI_UNKNOWN;
+  return GDB_OSABI_AIX;
 }
 
 static void
-- 
1.7.9.5