[Bug c/47418] warning: array subscript is above array bounds at O2 with sin6_addr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47418 Richard Guenther rguenth at gcc dot gnu.org changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2011.01.25 11:24:58 Ever Confirmed|0 |1 --- Comment #4 from Richard Guenther rguenth at gcc dot gnu.org 2011-01-25 11:24:58 UTC --- VRP sees bb 2: D.2725_3 = u.sa_data[15]; D.2726_4 = (int) D.2725_3; D.2728_6 = u.sa_data[14]; D.2729_7 = (int) D.2728_6; ... D.2769_47 = u.sa_data[0]; D.2770_48 = (int) D.2769_47; test_func (0, D.2770_48, D.2768_46, D.2765_43, D.2762_40, D.2759_37, D.2756_34, D.2753_31, D.2750_28, D.2747_25, D.2744_22, D.2741_19, D.2738_16, D.2735_13, D.2732_10, D.2729_7, D.2726_4); return 0; because of our fancy way of re-building non-addressed components. With 4.6 the warning is gone and we instead have (thanks to MEM-REF): bb 2: D.2695_3 = MEM[(char *)u + 15B]; D.2696_4 = (int) D.2695_3; D.2698_6 = MEM[(char *)u + 14B]; D.2699_7 = (int) D.2698_6; ... D.2740_48 = (int) D.2739_47; test_func (0, D.2740_48, D.2738_46, D.2735_43, D.2732_40, D.2729_37, D.2726_34, D.2723_31, D.2720_28, D.2717_25, D.2714_22, D.2711_19, D.2708_16, D.2705_13, D.2702_10, D.2699_7, D.2696_4); return 0; thus, no more array access and still non-address-taken u. 4.4 also warns about small-test.c: In function 'main': small-test.c:18: warning: array subscript is above array bounds small-test.c:18: warning: array subscript is above array bounds small-test.c:18: warning: array subscript is above array bounds small-test.c:18: warning: 'u' is used uninitialized in this function 4.3 doesn't warn at all. Confirmed. I'd close it as fixed in 4.6 and add a testcase (no time for that right now).
[Bug c/47418] warning: array subscript is above array bounds at O2 with sin6_addr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47418 --- Comment #1 from Dan McGee dpmcgee at gmail dot com 2011-01-23 00:15:29 UTC --- Also of note is the commented bit in the test case- if you instead dereference the s6_addr bit of the union, it all works without warnings. In the preprocessed source, replace ap = (char *)u.sin6.sin6_addr; with: ap = (char *)u.sin6.sin6_addr.__in6_u.__u6_addr8;
[Bug c/47418] warning: array subscript is above array bounds at O2 with sin6_addr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47418 Xavier chantry.xavier at gmail dot com changed: What|Removed |Added CC||chantry.xavier at gmail dot ||com --- Comment #2 from Xavier chantry.xavier at gmail dot com 2011-01-23 02:02:18 UTC --- (In reply to comment #1) Also of note is the commented bit in the test case- if you instead dereference the s6_addr bit of the union, it all works without warnings. In the preprocessed source, replace ap = (char *)u.sin6.sin6_addr; with: ap = (char *)u.sin6.sin6_addr.__in6_u.__u6_addr8; Actually it works with any member from __in6.u union. It seems gcc gets confused with the other anonymous union, and use the size of struct sockaddr instead of struct sockaddr_in6. I've got a simpler testcase which shows another interesting information : gcc gets confused when the sign of ap is the same as the size of the smallest struct/array of the union, and different from the sign of the big member that should be used.
[Bug c/47418] warning: array subscript is above array bounds at O2 with sin6_addr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47418 --- Comment #3 from Xavier chantry.xavier at gmail dot com 2011-01-23 02:06:35 UTC --- Created attachment 23084 -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=23084 simpler testcase $ gcc -O3 -Wall -c small-test.c small-test.c: In function 'main': small-test.c:18:51: warning: array subscript is above array bounds small-test.c:18:43: warning: array subscript is above array bounds small-test.c:18:35: warning: array subscript is above array bounds so gcc seems to think that the size of ap is 13 instead of 16. It's important that ap and sa_data are both char, and u6_addr8 is unsigned char. Same warning if ap and sa_data are unsigned char and u6_addr8 is char. But other combinations apparently do not give any warning.
