| Message ID | 20191128033959.87715-1-pihsun@chromium.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Johannes Berg |
| Headers | show |
| Series | [RESEND] wireless: Use offsetof instead of custom macro. | expand |
On Thu, 2019-11-28 at 11:39 +0800, Pi-Hsun Shih wrote: > Use offsetof to calculate offset of a field to take advantage of > compiler built-in version when possible, and avoid UBSAN warning when > compiling with Clang: [] > diff --git a/include/uapi/linux/wireless.h b/include/uapi/linux/wireless.h [] > @@ -1090,8 +1090,7 @@ struct iw_event { > /* iw_point events are special. First, the payload (extra data) come at > * the end of the event, so they are bigger than IW_EV_POINT_LEN. Second, > * we omit the pointer, so start at an offset. */ > -#define IW_EV_POINT_OFF (((char *) &(((struct iw_point *) NULL)->length)) - \ > - (char *) NULL) > +#define IW_EV_POINT_OFF offsetof(struct iw_point, length) > #define IW_EV_POINT_LEN (IW_EV_LCP_LEN + sizeof(struct iw_point) - \ > IW_EV_POINT_OFF) This is uapi. Is offsetof guaranteed to be available? Perhaps this is better without using another macro #define IW_EV_POINT_OFF ((size_t)&((struct iw_point *)NULL)->length)
On Thu, Nov 28, 2019 at 11:54 AM Joe Perches <joe@perches.com> wrote: > > On Thu, 2019-11-28 at 11:39 +0800, Pi-Hsun Shih wrote: > > Use offsetof to calculate offset of a field to take advantage of > > compiler built-in version when possible, and avoid UBSAN warning when > > compiling with Clang: > [] > > diff --git a/include/uapi/linux/wireless.h b/include/uapi/linux/wireless.h > [] > > @@ -1090,8 +1090,7 @@ struct iw_event { > > /* iw_point events are special. First, the payload (extra data) come at > > * the end of the event, so they are bigger than IW_EV_POINT_LEN. Second, > > * we omit the pointer, so start at an offset. */ > > -#define IW_EV_POINT_OFF (((char *) &(((struct iw_point *) NULL)->length)) - \ > > - (char *) NULL) > > +#define IW_EV_POINT_OFF offsetof(struct iw_point, length) > > #define IW_EV_POINT_LEN (IW_EV_LCP_LEN + sizeof(struct iw_point) - \ > > IW_EV_POINT_OFF) > > This is uapi. Is offsetof guaranteed to be available? offsetof is already used in other uapi headers (include/uapi/linux/fuse.h FUSE_NAME_OFFSET). Also offsetof is also defined back in C89 standard (in stddef.h), so it should be widely available and should be fine to use here? (Should I add a #ifndef __KERNEL__ #include <stddef.h> to the file?) > > Perhaps this is better without using another macro > > #define IW_EV_POINT_OFF ((size_t)&((struct iw_point *)NULL)->length) Clang UBSAN would still complain about this, since it's the same pattern as the original one. >
On Thu, Nov 28, 2019 at 8:05 PM Pi-Hsun Shih <pihsun@chromium.org> wrote: > > On Thu, Nov 28, 2019 at 11:54 AM Joe Perches <joe@perches.com> wrote: > > > > On Thu, 2019-11-28 at 11:39 +0800, Pi-Hsun Shih wrote: > > > Use offsetof to calculate offset of a field to take advantage of > > > compiler built-in version when possible, and avoid UBSAN warning when > > > compiling with Clang: > > [] > > > diff --git a/include/uapi/linux/wireless.h b/include/uapi/linux/wireless.h > > [] > > > @@ -1090,8 +1090,7 @@ struct iw_event { > > > /* iw_point events are special. First, the payload (extra data) come at > > > * the end of the event, so they are bigger than IW_EV_POINT_LEN. Second, > > > * we omit the pointer, so start at an offset. */ > > > -#define IW_EV_POINT_OFF (((char *) &(((struct iw_point *) NULL)->length)) - \ > > > - (char *) NULL) > > > +#define IW_EV_POINT_OFF offsetof(struct iw_point, length) > > > #define IW_EV_POINT_LEN (IW_EV_LCP_LEN + sizeof(struct iw_point) - \ > > > IW_EV_POINT_OFF) > > > > This is uapi. Is offsetof guaranteed to be available? > > offsetof is already used in other uapi headers > (include/uapi/linux/fuse.h FUSE_NAME_OFFSET). > > Also offsetof is also defined back in C89 standard (in stddef.h), so > it should be widely available and should be fine to use here? > (Should I add a #ifndef __KERNEL__ #include <stddef.h> to the file?) Yes, please, otherwise userspace could have a -Wimplicit-function-definition warning from including this header, since it would look like a function call to a previously undeclared function. Actually, it looks like include/uapi/linux/posix_types.h includes it unconditionally, and many other headers under include/uapi/ include include/uapi/linux/posix_types.h (unconditionally). So it may be ok to just include stddef.h unconditionally, but please do so in addition to the current diff you have.
diff --git a/include/uapi/linux/wireless.h b/include/uapi/linux/wireless.h index 86eca3208b6b..f259cca5cc2b 100644 --- a/include/uapi/linux/wireless.h +++ b/include/uapi/linux/wireless.h @@ -1090,8 +1090,7 @@ struct iw_event { /* iw_point events are special. First, the payload (extra data) come at * the end of the event, so they are bigger than IW_EV_POINT_LEN. Second, * we omit the pointer, so start at an offset. */ -#define IW_EV_POINT_OFF (((char *) &(((struct iw_point *) NULL)->length)) - \ - (char *) NULL) +#define IW_EV_POINT_OFF offsetof(struct iw_point, length) #define IW_EV_POINT_LEN (IW_EV_LCP_LEN + sizeof(struct iw_point) - \ IW_EV_POINT_OFF)
Use offsetof to calculate offset of a field to take advantage of compiler built-in version when possible, and avoid UBSAN warning when compiling with Clang: ================================================================== UBSAN: Undefined behaviour in net/wireless/wext-core.c:525:14 member access within null pointer of type 'struct iw_point' CPU: 3 PID: 165 Comm: kworker/u16:3 Tainted: G S W 4.19.23 #43 Workqueue: cfg80211 __cfg80211_scan_done [cfg80211] Call trace: dump_backtrace+0x0/0x194 show_stack+0x20/0x2c __dump_stack+0x20/0x28 dump_stack+0x70/0x94 ubsan_epilogue+0x14/0x44 ubsan_type_mismatch_common+0xf4/0xfc __ubsan_handle_type_mismatch_v1+0x34/0x54 wireless_send_event+0x3cc/0x470 ___cfg80211_scan_done+0x13c/0x220 [cfg80211] __cfg80211_scan_done+0x28/0x34 [cfg80211] process_one_work+0x170/0x35c worker_thread+0x254/0x380 kthread+0x13c/0x158 ret_from_fork+0x10/0x18 =================================================================== Signed-off-by: Pi-Hsun Shih <pihsun@chromium.org> --- include/uapi/linux/wireless.h | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) base-commit: 1875ff320f14afe21731a6e4c7b46dd33e45dfaa