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* [Bug middle-end/95667] New: warning for memset writing across multiple members @ 2020-06-13 23:36 msebor at gcc dot gnu.org 2020-06-13 23:38 ` [Bug middle-end/95667] [11 Regression] unintended " msebor at gcc dot gnu.org ` (4 more replies) 0 siblings, 5 replies; 6+ messages in thread From: msebor at gcc dot gnu.org @ 2020-06-13 23:36 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95667 Bug ID: 95667 Summary: warning for memset writing across multiple members Product: gcc Version: 10.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: msebor at gcc dot gnu.org Target Milestone: --- Although strictly correct, GCC usually avoids warning for calls to memcpy that write into multiple members at the same time, up to the size of the complete object. This is done because the Linux kernel does these things in a few places. As dangerous as the practice is, the change committed to resolve pr95353 (r11-1183) tried to preserve this behavior for now (in the future I'd like to add a new warning option to control it), but the test case below shows it didn't preserve the GCC 10 and prior behavior in this case (same with memcpy). $ cat z.c && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout z.c struct S { char a[3], b[5]; }; void* f (void) { struct S *p = __builtin_malloc (sizeof *p); char s[] = "1234567"; __builtin_strcpy (p->a, s); // warning (good) return p; } void* g (void) { struct S *p = __builtin_malloc (sizeof *p); __builtin_memset (p->a, 0, 8); // warning not expected (yet) return p; } z.c: In function ‘f’: z.c:7:3: warning: ‘__builtin_strcpy’ writing 8 bytes into a region of size 3 [-Wstringop-overflow=] 7 | __builtin_strcpy (p->a, s); // warning (good) | ^~~~~~~~~~~~~~~~~~~~~~~~~~ z.c:1:17: note: at offset 0 to object ‘a’ with size 3 declared here 1 | struct S { char a[3], b[5]; }; | ^ ;; Function f (f, funcdef_no=0, decl_uid=1934, cgraph_uid=1, symbol_order=0) f () { char s[8]; struct S * p; long unsigned int _8; <bb 2> [local count: 1073741824]: p_4 = __builtin_malloc (8); s = "1234567"; _8 = MEM <long unsigned int> [(char * {ref-all})&s]; MEM <long unsigned int> [(char * {ref-all})p_4] = _8; s ={v} {CLOBBER}; return p_4; } ;; Function g (g, funcdef_no=1, decl_uid=1939, cgraph_uid=2, symbol_order=1) g () { struct S * p; char[3] * _1; <bb 2> [local count: 1073741824]: p_4 = __builtin_malloc (8); _1 = &p_4->a; __builtin_memset (_1, 0, 8); return p_4; } z.c: In function ‘g’: z.c:14:3: warning: ‘__builtin_memset’ writing 8 bytes into a region of size 3 overflows the destination [-Wstringop-overflow=] 14 | __builtin_memset (p->a, 0, 8); // warning not expected (yet) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ z.c:1:17: note: destination object ‘a’ 1 | struct S { char a[3], b[5]; }; | ^ ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/95667] [11 Regression] unintended warning for memset writing across multiple members 2020-06-13 23:36 [Bug middle-end/95667] New: warning for memset writing across multiple members msebor at gcc dot gnu.org @ 2020-06-13 23:38 ` msebor at gcc dot gnu.org 2020-06-15 6:49 ` rguenth at gcc dot gnu.org ` (3 subsequent siblings) 4 siblings, 0 replies; 6+ messages in thread From: msebor at gcc dot gnu.org @ 2020-06-13 23:38 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95667 Martin Sebor <msebor at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |ASSIGNED Last reconfirmed| |2020-06-13 Blocks| |88443 Assignee|unassigned at gcc dot gnu.org |msebor at gcc dot gnu.org Keywords| |diagnostic Ever confirmed|0 |1 Summary|warning for memset writing |[11 Regression] unintended |across multiple members |warning for memset writing | |across multiple members --- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> --- See https://gcc.gnu.org/pipermail/gcc-patches/2020-June/548040.html for the original report. Referenced Bugs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88443 [Bug 88443] [meta-bug] bogus/missing -Wstringop-overflow warnings ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/95667] [11 Regression] unintended warning for memset writing across multiple members 2020-06-13 23:36 [Bug middle-end/95667] New: warning for memset writing across multiple members msebor at gcc dot gnu.org 2020-06-13 23:38 ` [Bug middle-end/95667] [11 Regression] unintended " msebor at gcc dot gnu.org @ 2020-06-15 6:49 ` rguenth at gcc dot gnu.org 2020-06-18 15:32 ` msebor at gcc dot gnu.org ` (2 subsequent siblings) 4 siblings, 0 replies; 6+ messages in thread From: rguenth at gcc dot gnu.org @ 2020-06-15 6:49 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95667 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Target Milestone|--- |11.0 Version|10.0 |11.0 ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/95667] [11 Regression] unintended warning for memset writing across multiple members 2020-06-13 23:36 [Bug middle-end/95667] New: warning for memset writing across multiple members msebor at gcc dot gnu.org 2020-06-13 23:38 ` [Bug middle-end/95667] [11 Regression] unintended " msebor at gcc dot gnu.org 2020-06-15 6:49 ` rguenth at gcc dot gnu.org @ 2020-06-18 15:32 ` msebor at gcc dot gnu.org 2020-06-18 18:02 ` cvs-commit at gcc dot gnu.org 2020-08-20 16:37 ` msebor at gcc dot gnu.org 4 siblings, 0 replies; 6+ messages in thread From: msebor at gcc dot gnu.org @ 2020-06-18 15:32 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95667 Martin Sebor <msebor at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |patch --- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> --- Patch: https://gcc.gnu.org/pipermail/gcc-patches/2020-June/548511.html ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/95667] [11 Regression] unintended warning for memset writing across multiple members 2020-06-13 23:36 [Bug middle-end/95667] New: warning for memset writing across multiple members msebor at gcc dot gnu.org ` (2 preceding siblings ...) 2020-06-18 15:32 ` msebor at gcc dot gnu.org @ 2020-06-18 18:02 ` cvs-commit at gcc dot gnu.org 2020-08-20 16:37 ` msebor at gcc dot gnu.org 4 siblings, 0 replies; 6+ messages in thread From: cvs-commit at gcc dot gnu.org @ 2020-06-18 18:02 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95667 --- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Martin Sebor <msebor@gcc.gnu.org>: https://gcc.gnu.org/g:5acc654e380797bbf402bc3a0a67f9a6ac4c2a83 commit r11-1517-g5acc654e380797bbf402bc3a0a67f9a6ac4c2a83 Author: Martin Sebor <msebor@redhat.com> Date: Thu Jun 18 12:00:36 2020 -0600 Avoid warning for memset writing over multiple members. Resolves: PR middle-end/95667 - unintended warning for memset writing across multiple members PR middle-end/92814 - missing -Wstringop-overflow writing into a dynamically allocated flexible array member gcc/ChangeLog: PR middle-end/95667 PR middle-end/92814 * builtins.c (compute_objsize): Remove call to compute_builtin_object_size and instead compute conservative sizes directly here. gcc/testsuite/ChangeLog: PR middle-end/95667 PR middle-end/92814 * gcc.dg/Wstringop-overflow-25.c: Remove xfails. * gcc.dg/Wstringop-overflow-39.c: New test. ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/95667] [11 Regression] unintended warning for memset writing across multiple members 2020-06-13 23:36 [Bug middle-end/95667] New: warning for memset writing across multiple members msebor at gcc dot gnu.org ` (3 preceding siblings ...) 2020-06-18 18:02 ` cvs-commit at gcc dot gnu.org @ 2020-08-20 16:37 ` msebor at gcc dot gnu.org 4 siblings, 0 replies; 6+ messages in thread From: msebor at gcc dot gnu.org @ 2020-08-20 16:37 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95667 Martin Sebor <msebor at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |FIXED Status|ASSIGNED |RESOLVED --- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> --- Fixed in r11-1517. ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-08-20 16:37 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2020-06-13 23:36 [Bug middle-end/95667] New: warning for memset writing across multiple members msebor at gcc dot gnu.org 2020-06-13 23:38 ` [Bug middle-end/95667] [11 Regression] unintended " msebor at gcc dot gnu.org 2020-06-15 6:49 ` rguenth at gcc dot gnu.org 2020-06-18 15:32 ` msebor at gcc dot gnu.org 2020-06-18 18:02 ` cvs-commit at gcc dot gnu.org 2020-08-20 16:37 ` msebor at gcc dot gnu.org
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