diff mbox

Get rid of array-bounds warning in __kernel_rem_pio2[f] with gcc 6.1 -O3.

Message ID nn5cpo$pfn$1@ger.gmane.org
State Superseded
Headers show

Commit Message

Stefan Liebler July 25, 2016, 3:55 p.m. UTC
On 07/20/2016 06:33 PM, Joseph Myers wrote:
> On Thu, 7 Jul 2016, Stefan Liebler wrote:
>
>> Hi,
>>
>> while testing, I've got the following werror on s390x when build with gcc 6.1
>> (or current gcc head) and -O3:
>> ../sysdeps/ieee754/dbl-64/k_rem_pio2.c: In function ‘__kernel_rem_pio2’:
>> ../sysdeps/ieee754/dbl-64/k_rem_pio2.c:254:18: error: array subscript is below
>> array bounds [-Werror=array-bounds]
>>      for (k = 1; iq[jk - k] == 0; k++)
>>                  ~~^~~~~~~~
>>
>> I get the same error with sysdeps/ieee754/flt-32/k_rem_pio2f.c.
>>
>> Does anybody else get this warning on another architecture, too?
>>
>> This patch adds a check so that the index is always >= 0.
>
> Such an unnecessary check is not how we deal with bogus warnings.
> Rather, use the DIAG_*_NEEDS_COMMENT macros from include/libc-internal.h,
> with a detailed comment explaining what the warning is and why it is a
> false positive.
>

Sorry for the delay. Here is the updated patch with DIAG_* macros.
Is this okay?

Bye Stefan

ChangeLog:


ChangeLog:

	* sysdeps/ieee754/dbl-64/k_rem_pio2.c (__kernel_rem_pio2):
	Use DIAG_*_NEEDS_COMMENT macro to get rid of array-bounds
	warning.
	* sysdeps/ieee754/flt-32/k_rem_pio2f.c (__kernel_rem_pio2f):
	Likewise.

Comments

Mike Frysinger Aug. 1, 2016, 2:12 p.m. UTC | #1
On 25 Jul 2016 17:55, Stefan Liebler wrote:
> +	  /* On s390x gcc 6.1 -O3 produces the warning "array subscript is below
> +	     array bounds [-Werror=array-bounds]". Only __ieee754_rem_pio2l()
> +	     calls __kernel_rem_pio2f() for normal numbers and |x| > 3pi/4. Thus
> +	     x can't be zero and ipio2 is not zero, too. Thus not all iq[]
> +	     values can't be zero.  */

GNU style puts two spaces after the period
-mike
diff mbox

Patch

diff --git a/sysdeps/ieee754/dbl-64/k_rem_pio2.c b/sysdeps/ieee754/dbl-64/k_rem_pio2.c
index e58c9e8..4fa05b9 100644
--- a/sysdeps/ieee754/dbl-64/k_rem_pio2.c
+++ b/sysdeps/ieee754/dbl-64/k_rem_pio2.c
@@ -132,6 +132,7 @@  static char rcsid[] = "$NetBSD: k_rem_pio2.c,v 1.7 1995/05/10 20:46:25 jtc Exp $
 
 #include <math.h>
 #include <math_private.h>
+#include <libc-internal.h>
 
 static const int init_jk[] = {2,3,4,6}; /* initial value for jk */
 
@@ -251,8 +252,16 @@  recompute:
 	j |= iq[i];
       if (j == 0)      /* need recomputation */
 	{
+	  /* On s390x gcc 6.1 -O3 produces the warning "array subscript is below
+	     array bounds [-Werror=array-bounds]". Only __ieee754_rem_pio2l()
+	     calls __kernel_rem_pio2f() for normal numbers and |x| > 3pi/4. Thus
+	     x can't be zero and ipio2 is not zero, too. Thus not all iq[]
+	     values can't be zero.  */
+	  DIAG_PUSH_NEEDS_COMMENT;
+	  DIAG_IGNORE_NEEDS_COMMENT (6.1, "-Warray-bounds");
 	  for (k = 1; iq[jk - k] == 0; k++)
 	    ;                               /* k = no. of terms needed */
+	  DIAG_POP_NEEDS_COMMENT;
 
 	  for (i = jz + 1; i <= jz + k; i++) /* add q[jz+1] to q[jz+k] */
 	    {
diff --git a/sysdeps/ieee754/flt-32/k_rem_pio2f.c b/sysdeps/ieee754/flt-32/k_rem_pio2f.c
index 392afdb..83d3214 100644
--- a/sysdeps/ieee754/flt-32/k_rem_pio2f.c
+++ b/sysdeps/ieee754/flt-32/k_rem_pio2f.c
@@ -19,6 +19,7 @@  static char rcsid[] = "$NetBSD: k_rem_pio2f.c,v 1.4 1995/05/10 20:46:28 jtc Exp
 
 #include <math.h>
 #include <math_private.h>
+#include <libc-internal.h>
 
 /* In the float version, the input parameter x contains 8 bit
    integers, not 24 bit integers.  113 bit precision is not supported.  */
@@ -122,7 +123,15 @@  recompute:
 	    j = 0;
 	    for (i=jz-1;i>=jk;i--) j |= iq[i];
 	    if(j==0) { /* need recomputation */
+		/* On s390x gcc 6.1 -O3 produces the warning "array subscript is
+		   below array bounds [-Werror=array-bounds]". Only
+		   __ieee754_rem_pio2f() calls __kernel_rem_pio2f() for normal
+		   numbers and |x| ~> 2^7*(pi/2). Thus x can't be zero and ipio2
+		   is not zero, too. Thus not all iq[] values can't be zero.  */
+		DIAG_PUSH_NEEDS_COMMENT;
+		DIAG_IGNORE_NEEDS_COMMENT (6.1, "-Warray-bounds");
 		for(k=1;iq[jk-k]==0;k++);   /* k = no. of terms needed */
+		DIAG_POP_NEEDS_COMMENT;
 
 		for(i=jz+1;i<=jz+k;i++) {   /* add q[jz+1] to q[jz+k] */
 		    f[jx+i] = (float) ipio2[jv+i];