[glibc/azanella/master-posix_clock] Fix build warnings in resolv/res_send.c

[Adhemerval Zanella <azanella@sourceware.org>]

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=d1bc2cbbed9aea2017ef941f63c8786571da5b4f

commit d1bc2cbbed9aea2017ef941f63c8786571da5b4f
Author: Stefan Liebler <stli@linux.ibm.com>
Date:   Tue Jul 2 14:07:44 2019 +0200

    Fix build warnings in resolv/res_send.c
    
    This patch fixes the gcc warnings seen with gcc 9 -march>=z13 on s390x:
    res_send.c: In function ‘__res_context_send’:
    res_send.c:498:7: error: ‘resplen’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
      498 |    if (n == 0 && (buf2 == NULL || *resplen2 == 0))
          |       ^
    
    In this case send_vc is inlined into __res_context_send
    and the maybe uninitialized resplen belongs to the one in send_vc.
    
    In send_vc there is already a DIAG_IGNORE_NEEDS_COMMENT (5, "-Wmaybe-uninitialized")
    and a comment which explains that this is a false-positive.
    Note that resplen is used as return value.
    
    This patch adds a further DIAG_IGNORE_NEEDS_COMMENT around the declaration of n
    in __res_context_send and the comparison after n was set to the return value of send_vc.
    
    ChangeLog:
    
    	* resolv/res_send.c (__res_context_send): Disable maybe-uninitialized
    	warning.

Diff:
---
 ChangeLog         |  5 +++++
 resolv/res_send.c | 17 ++++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 0c7bdd0..3e4d87f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2019-07-02  Stefan Liebler  <stli@linux.ibm.com>
+
+	* resolv/res_send.c (__res_context_send): Disable maybe-uninitialized
+	warning.
+
 2019-07-01  Florian Weimer  <fweimer@redhat.com>
 
 	* scripts/build-many-glibcs.py (Context.add_all_configs): Add v4t
diff --git a/resolv/res_send.c b/resolv/res_send.c
index eeeb8ac..ed27f3a 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -401,7 +401,18 @@ __res_context_send (struct resolv_context *ctx,
 		    int *nansp2, int *resplen2, int *ansp2_malloced)
 {
 	struct __res_state *statp = ctx->resp;
-	int gotsomewhere, terrno, try, v_circuit, resplen, n;
+	int gotsomewhere, terrno, try, v_circuit, resplen;
+	/* On some architectures send_vc is inlined and the compiler might emit
+	   a warning indicating 'resplen' may be used uninitialized.  Note that
+	   the warning belongs to resplen in send_vc which is used as return
+	   value!  There the maybe-uninitialized warning is already ignored as
+	   it is a false-positive - see comment in send_vc.
+	   Here the variable n is set to the return value of send_vc.
+	   See below.  */
+	DIAG_PUSH_NEEDS_COMMENT;
+	DIAG_IGNORE_NEEDS_COMMENT (9, "-Wmaybe-uninitialized");
+	int n;
+	DIAG_POP_NEEDS_COMMENT;
 
 	if (statp->nscount == 0) {
 		__set_errno (ESRCH);
@@ -495,8 +506,12 @@ __res_context_send (struct resolv_context *ctx,
 				    ansp2_malloced);
 			if (n < 0)
 				return (-1);
+			/* See comment at the declaration of n.  */
+			DIAG_PUSH_NEEDS_COMMENT;
+			DIAG_IGNORE_NEEDS_COMMENT (9, "-Wmaybe-uninitialized");
 			if (n == 0 && (buf2 == NULL || *resplen2 == 0))
 				goto next_ns;
+			DIAG_POP_NEEDS_COMMENT;
 		} else {
 			/* Use datagrams. */
 			n = send_dg(statp, buf, buflen, buf2, buflen2,