| Message ID | 20241218145758.701008-1-aleksander.lobakin@intel.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | stddef: make __struct_group() UAPI C++-friendly | expand |
On December 18, 2024 6:57:58 AM PST, Alexander Lobakin <aleksander.lobakin@intel.com> wrote: >For the most part of C++ history, it couldn't have type declarations >inside anonymous unions for different reasons. At the same time, >__struct_group() relies on the latters, so when the @TAG argument >is not empty, C++ code doesn't want to build (even under >`extern "C"`): > >../linux/include/uapi/linux/pkt_cls.h:25:24: error: >'struct tc_u32_sel::<unnamed union>::tc_u32_sel_hdr,' invalid; >an anonymous union may only have public non-static data members >[-fpermissive] > >The safest way to fix this without trying to switch standards (which >is impossible in UAPI anyway) etc., is to disable tag declaration >for that language. This won't break anything since for now it's not >buildable at all. >Use a separate definition for __struct_group() when __cplusplus is >defined to mitigate the error, including the version from tools/. > >Fixes: 50d7bd38c3aa ("stddef: Introduce struct_group() helper macro") >Reported-by: Christopher Ferris <cferris@google.com> >Closes: https://lore.kernel.org/linux-hardening/Z1HZpe3WE5As8UAz@google.com >Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com> >--- > include/uapi/linux/stddef.h | 12 ++++++++++-- > tools/include/uapi/linux/stddef.h | 14 +++++++++++--- > 2 files changed, 21 insertions(+), 5 deletions(-) > >diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h >index 58154117d9b0..ad51b1362bbb 100644 >--- a/include/uapi/linux/stddef.h >+++ b/include/uapi/linux/stddef.h >@@ -20,14 +20,22 @@ > * and size: one anonymous and one named. The former's members can be used > * normally without sub-struct naming, and the latter can be used to > * reason about the start, end, and size of the group of struct members. >- * The named struct can also be explicitly tagged for layer reuse, as well >- * as both having struct attributes appended. >+ * The named struct can also be explicitly tagged for layer reuse (C only), >+ * as well as both having struct attributes appended. > */ >+#ifndef __cplusplus > #define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \ > union { \ > struct { MEMBERS } ATTRS; \ > struct TAG { MEMBERS } ATTRS NAME; \ > } ATTRS >+#else >+#define __struct_group(__IGNORED, NAME, ATTRS, MEMBERS...) \ >+ union { \ >+ struct { MEMBERS } ATTRS; \ >+ struct { MEMBERS } ATTRS NAME; \ >+ } ATTRS >+#endif Instead of copying the entire define, what about just wrapping the tag? #ifdef __cplusplus #define __struct_group_tag(TAG) #else #define __struct_group_tag(TAG) TAG #endif #define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \ union { \ struct { MEMBERS } ATTRS; \ struct __struct_group_tag(TAG) { MEMBERS } ATTRS NAME; \ } ATTRS -Kees > > #ifdef __cplusplus > /* sizeof(struct{}) is 1 in C++, not 0, can't use C version of the macro. */ >diff --git a/tools/include/uapi/linux/stddef.h b/tools/include/uapi/linux/stddef.h >index bb6ea517efb5..12b854ecc215 100644 >--- a/tools/include/uapi/linux/stddef.h >+++ b/tools/include/uapi/linux/stddef.h >@@ -20,14 +20,22 @@ > * and size: one anonymous and one named. The former's members can be used > * normally without sub-struct naming, and the latter can be used to > * reason about the start, end, and size of the group of struct members. >- * The named struct can also be explicitly tagged for layer reuse, as well >- * as both having struct attributes appended. >+ * The named struct can also be explicitly tagged for layer reuse (C only), >+ * as well as both having struct attributes appended. > */ >+#ifndef __cplusplus > #define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \ > union { \ > struct { MEMBERS } ATTRS; \ > struct TAG { MEMBERS } ATTRS NAME; \ >- } >+ } ATTRS >+#else >+#define __struct_group(__IGNORED, NAME, ATTRS, MEMBERS...) \ >+ union { \ >+ struct { MEMBERS } ATTRS; \ >+ struct { MEMBERS } ATTRS NAME; \ >+ } ATTRS >+#endif > > /** > * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h index 58154117d9b0..ad51b1362bbb 100644 --- a/include/uapi/linux/stddef.h +++ b/include/uapi/linux/stddef.h @@ -20,14 +20,22 @@ * and size: one anonymous and one named. The former's members can be used * normally without sub-struct naming, and the latter can be used to * reason about the start, end, and size of the group of struct members. - * The named struct can also be explicitly tagged for layer reuse, as well - * as both having struct attributes appended. + * The named struct can also be explicitly tagged for layer reuse (C only), + * as well as both having struct attributes appended. */ +#ifndef __cplusplus #define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \ union { \ struct { MEMBERS } ATTRS; \ struct TAG { MEMBERS } ATTRS NAME; \ } ATTRS +#else +#define __struct_group(__IGNORED, NAME, ATTRS, MEMBERS...) \ + union { \ + struct { MEMBERS } ATTRS; \ + struct { MEMBERS } ATTRS NAME; \ + } ATTRS +#endif #ifdef __cplusplus /* sizeof(struct{}) is 1 in C++, not 0, can't use C version of the macro. */ diff --git a/tools/include/uapi/linux/stddef.h b/tools/include/uapi/linux/stddef.h index bb6ea517efb5..12b854ecc215 100644 --- a/tools/include/uapi/linux/stddef.h +++ b/tools/include/uapi/linux/stddef.h @@ -20,14 +20,22 @@ * and size: one anonymous and one named. The former's members can be used * normally without sub-struct naming, and the latter can be used to * reason about the start, end, and size of the group of struct members. - * The named struct can also be explicitly tagged for layer reuse, as well - * as both having struct attributes appended. + * The named struct can also be explicitly tagged for layer reuse (C only), + * as well as both having struct attributes appended. */ +#ifndef __cplusplus #define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \ union { \ struct { MEMBERS } ATTRS; \ struct TAG { MEMBERS } ATTRS NAME; \ - } + } ATTRS +#else +#define __struct_group(__IGNORED, NAME, ATTRS, MEMBERS...) \ + union { \ + struct { MEMBERS } ATTRS; \ + struct { MEMBERS } ATTRS NAME; \ + } ATTRS +#endif /** * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
For the most part of C++ history, it couldn't have type declarations inside anonymous unions for different reasons. At the same time, __struct_group() relies on the latters, so when the @TAG argument is not empty, C++ code doesn't want to build (even under `extern "C"`): ../linux/include/uapi/linux/pkt_cls.h:25:24: error: 'struct tc_u32_sel::<unnamed union>::tc_u32_sel_hdr,' invalid; an anonymous union may only have public non-static data members [-fpermissive] The safest way to fix this without trying to switch standards (which is impossible in UAPI anyway) etc., is to disable tag declaration for that language. This won't break anything since for now it's not buildable at all. Use a separate definition for __struct_group() when __cplusplus is defined to mitigate the error, including the version from tools/. Fixes: 50d7bd38c3aa ("stddef: Introduce struct_group() helper macro") Reported-by: Christopher Ferris <cferris@google.com> Closes: https://lore.kernel.org/linux-hardening/Z1HZpe3WE5As8UAz@google.com Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com> --- include/uapi/linux/stddef.h | 12 ++++++++++-- tools/include/uapi/linux/stddef.h | 14 +++++++++++--- 2 files changed, 21 insertions(+), 5 deletions(-)