[PATCH] Fix -Os related -Werror failures.

[Carlos O'Donell <carlos at redhat dot com>]

While investigating bug 20729 I decided to fix up the -Wmaybe-uninitialized
errors caused by building with -Os rather than build with -Wno-error.
The comments provide all the details.

No regressions on x86_64 and x86 (building with -O2). There are _tons_
of failures building with -Os, but nothing that is novel, lots of linkspace
failures because of lack of inlining, and lots of extra PLT references that
should not be in the dynamic loader, all things that would need fixing.

Is there value in checking in these fixes then to let others work out the
-Os failures?

2016-10-27  Carlos O'Donell  <carlos@redhat.com>

	* iso-2022-cn-ext.c: Include libc-internal.h and ignore
	-Wmaybe-uninitialized for BODY macro.
	* locale/weight.h (findix): Ignore -Wmaybe-uninitialized error
	for seq2.back_us and seq1.back_us.
	* locale/weightwc.h (findix): Likewise.
	* nptl_db/thread_dbP.h: Ignore -Wmaybe-uninitialized error for
	DB_GET_FIELD_ADDRESS.
	* resolv/res_send (reopen): Ignore -Wmaybe-uninitialized error for
	slen.
	* string/strcoll_l.c (get_next_seq): Ignore -Wmaybe-uninitialized
	for seq2.save_idx and seq1.save_idx.

diff --git a/iconvdata/iso-2022-cn-ext.c b/iconvdata/iso-2022-cn-ext.c
index df5b5df..6c9fc97 100644
--- a/iconvdata/iso-2022-cn-ext.c
+++ b/iconvdata/iso-2022-cn-ext.c
@@ -27,6 +27,7 @@
 #include "cns11643.h"
 #include "cns11643l1.h"
 #include "cns11643l2.h"
+#include <libc-internal.h>
 
 #include <assert.h>
 
@@ -394,6 +395,16 @@ enum
 #define MIN_NEEDED_OUTPUT	TO_LOOP_MIN_NEEDED_TO
 #define MAX_NEEDED_OUTPUT	TO_LOOP_MAX_NEEDED_TO
 #define LOOPFCT			TO_LOOP
+/* With GCC 5.3 when compiling with -Os the compiler emits a warning
+   that buf[0] and buf[1] may be used uninitialized.  This can only
+   happen in the case where tmpbuf[3] is used, and in that case the
+   write to the tmpbuf[1] and tmpbuf[2] was assured because
+   ucs4_to_cns11643 would have filled in those entries.  The difficulty
+   is in getting the compiler to see this logic because tmpbuf[0] is
+   involved in determining the code page and is the indicator that
+   tmpbuf[2] is initialized.  */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (5.3, "-Wmaybe-uninitialized");
 #define BODY \
   {									      \
     uint32_t ch;							      \
@@ -645,6 +656,7 @@ enum
     /* Now that we wrote the output increment the input pointer.  */	      \
     inptr += 4;								      \
   }
+DIAG_POP_NEEDS_COMMENT;
 #define EXTRA_LOOP_DECLS	, int *setp
 #define INIT_PARAMS		int set = (*setp >> 3) & CURRENT_MASK; \
 				int ann = (*setp >> 3) & ~CURRENT_MASK
diff --git a/locale/weight.h b/locale/weight.h
index c99730c..4c35313 100644
--- a/locale/weight.h
+++ b/locale/weight.h
@@ -61,9 +61,17 @@ findidx (const int32_t *table,
 	     already.  */
 	  size_t cnt;
 
+	  /* With GCC 5.3 when compiling with -Os the compiler warns
+	     that seq2.back_us, which becomes usrc, might be used
+	     uninitialized.  This can't be true because we pass a length
+	     of -1 for len at the same time which means that this loop
+	     never executes.  */
+	  DIAG_PUSH_NEEDS_COMMENT;
+	  DIAG_IGNORE_NEEDS_COMMENT (5.3, "-Wmaybe-uninitialized");
 	  for (cnt = 0; cnt < nhere && cnt < len; ++cnt)
 	    if (cp[cnt] != usrc[cnt])
 	      break;
+	  DIAG_POP_NEEDS_COMMENT;
 
 	  if (cnt == nhere)
 	    {
diff --git a/locale/weightwc.h b/locale/weightwc.h
index ab26482..5dcfb2e 100644
--- a/locale/weightwc.h
+++ b/locale/weightwc.h
@@ -59,9 +59,17 @@ findidx (const int32_t *table,
 	     already.  */
 	  size_t cnt;
 
+	  /* With GCC 5.3 when compiling with -Os the compiler warns
+	     that seq2.back_us, which becomes usrc, might be used
+	     uninitialized.  This can't be true because we pass a length
+	     of -1 for len at the same time which means that this loop
+	     never executes.  */
+	  DIAG_PUSH_NEEDS_COMMENT;
+	  DIAG_IGNORE_NEEDS_COMMENT (5.3, "-Wmaybe-uninitialized");
 	  for (cnt = 0; cnt < nhere && cnt < len; ++cnt)
 	    if (cp[cnt] != usrc[cnt])
 	      break;
+	  DIAG_POP_NEEDS_COMMENT;
 
 	  if (cnt == nhere)
 	    {
diff --git a/nptl_db/thread_dbP.h b/nptl_db/thread_dbP.h
index 39c3061..116a546 100644
--- a/nptl_db/thread_dbP.h
+++ b/nptl_db/thread_dbP.h
@@ -160,10 +160,19 @@ extern ps_err_e td_mod_lookup (struct ps_prochandle *ps, const char *modname,
 		   SYM_##type##_FIELD_##field, \
 		   (psaddr_t) 0 + (idx), (ptr), &(var))
 
+/* With GCC 5.3 when compiling with -Os the compiler emits a warning
+   that slot may be used uninitialized.  This is never the case since
+   the dynamic loader initializes the slotinfo list and
+   dtv_slotinfo_list will point slot at the first entry.  Therefore
+   when DB_GET_FIELD_ADDRESS is called with a slot for ptr, the slot is
+   always initialized.  */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_NEEDS_COMMENT (5.3, "-Wmaybe-uninitialized");
 #define DB_GET_FIELD_ADDRESS(var, ta, ptr, type, field, idx) \
   ((var) = (ptr), _td_locate_field ((ta), (ta)->ta_field_##type##_##field, \
 				    SYM_##type##_FIELD_##field, \
 				    (psaddr_t) 0 + (idx), &(var)))
+DIAG_POP_NEEDS_COMMENT;
 
 extern td_err_e _td_locate_field (td_thragent_t *ta,
 				  db_desc_t desc, int descriptor_name,
diff --git a/resolv/res_send.c b/resolv/res_send.c
index 6d46bb2..19a4c1f 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -930,7 +930,16 @@ reopen (res_state statp, int *terrno, int ns)
 		 * error message is received.  We can thus detect
 		 * the absence of a nameserver without timing out.
 		 */
+		/* With GCC 5.3 when compiling with -Os the compiler
+		   emits a warning that slen may be used uninitialized,
+		   but that is never true.  Both slen and
+		   EXT(statp).nssocks[ns] are initialized together or the
+		   function return -1 before control flow reaches the
+		   call to connect with slen.  */
+		DIAG_PUSH_NEEDS_COMMENT;
+		DIAG_IGNORE_NEEDS_COMMENT (5.3, "-Wmaybe-uninitialized");
 		if (connect(EXT(statp).nssocks[ns], nsap, slen) < 0) {
+		DIAG_POP_NEEDS_COMMENT;
 			Aerror(statp, stderr, "connect(dg)", errno, nsap);
 			__res_iclose(statp, false);
 			return (0);
diff --git a/string/strcoll_l.c b/string/strcoll_l.c
index 4d1e3ab..8e689ba 100644
--- a/string/strcoll_l.c
+++ b/string/strcoll_l.c
@@ -24,6 +24,7 @@
 #include <stdint.h>
 #include <string.h>
 #include <sys/param.h>
+#include <libc-internal.h>
 
 #ifndef STRING_TYPE
 # define STRING_TYPE char
@@ -170,7 +171,19 @@ get_next_seq (coll_seq *seq, int nrules, const unsigned char *rulesets,
 	    }
 	}
 
+      /* With GCC 5.3 when compiling with -Os the compiler complains
+	 that idx, taken from seq->idx (seq1 or seq2 from STRCOLL) may
+	 be used uninitialized.  In general this can't possibly be true
+	 since seq1.idx and seq2.idx are initialized to zero in the
+	 outer function.  Only one case where seq->idx is restored from
+	 seq->save_idx might result in an uninitialized idx value, but
+	 it is guarded by a sequence of checks against backw_stop which
+	 ensures that seq->save_idx was saved to first and contains a
+	 valid value.  */
+      DIAG_PUSH_NEEDS_COMMENT;
+      DIAG_IGNORE_NEEDS_COMMENT (5.3, "-Wmaybe-uninitialized");
       len = weights[idx++];
+      DIAG_POP_NEEDS_COMMENT;
       /* Skip over indices of previous levels.  */
       for (int i = 0; i < pass; i++)
 	{
---

-- 
Cheers,
Carlos.