Patchwork Fix build warnings in resolv/res_send.c

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Submitter Stefan Liebler
Date June 25, 2019, 1:18 p.m.
Message ID <de6e4add-1a9d-373c-7343-d055d4e4d80e@linux.ibm.com>
Download mbox | patch
Permalink /patch/33395/
State New
Headers show

Comments

Stefan Liebler - June 25, 2019, 1:18 p.m.
Hi,

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.

Bye
Stefan

ChangeLog:

	* resolv/res_send.c (__res_context_send):
	Disable maybe-uninitialized warning.
Stefan Liebler - July 1, 2019, 2:12 p.m.
On 6/25/19 3:18 PM, Stefan Liebler wrote:
> Hi,
> 
> 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.
> 
> Bye
> Stefan
> 
> ChangeLog:
> 
>      * resolv/res_send.c (__res_context_send):
>      Disable maybe-uninitialized warning.

ping

Patch

commit 6c3b01619ec2260a95bb7651e9c3a7aa3619745b
Author: Stefan Liebler <stli@linux.ibm.com>
Date:   Tue Jun 25 13:59:28 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 --git a/resolv/res_send.c b/resolv/res_send.c
index eeeb8acf27..ed27f3abf8 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,