> From: Scott Mitchell <[email protected]> > > Add __rte_may_alias attribute to unaligned_uint{16,32,64}_t typedefs > to prevent GCC strict-aliasing optimization bugs. GCC has a bug where > it incorrectly elides struct initialization when strict aliasing is > enabled, causing reads from uninitialized memory. > > The __rte_may_alias attribute signals to the compiler that these types > can alias other types, preventing the incorrect optimization.
I'm wondering if this is the right place to add __rte_may_alias, i.e. if the scope of the workaround is correct. Are the unaligned_uintNN_t types only used in a way where they are affected by the GCC bug? If not, adding __rte_may_alias to the types themselves may be too broad. Does the GCC bug only affect the unaligned_uintNN_t types? Or does it occur elsewhere or for other types too? Then this workaround only solves the problem for parts of the code. Minor detail: If the bug only occurs on GCC, not Clang, please make the workaround GCC-only, using the preprocessor. > > Signed-off-by: Scott Mitchell <[email protected]> > --- > lib/eal/include/rte_common.h | 34 +++++++++++++++++++--------------- > 1 file changed, 19 insertions(+), 15 deletions(-) > > diff --git a/lib/eal/include/rte_common.h > b/lib/eal/include/rte_common.h > index 9e7d84f929..ac70270cfb 100644 > --- a/lib/eal/include/rte_common.h > +++ b/lib/eal/include/rte_common.h > @@ -121,14 +121,27 @@ extern "C" { > #define __rte_aligned(a) __attribute__((__aligned__(a))) > #endif > > +/** > + * Macro to mark a type that is not subject to type-based aliasing > rules > + */ > +#ifdef RTE_TOOLCHAIN_MSVC > +#define __rte_may_alias > +#else > +#define __rte_may_alias __attribute__((__may_alias__)) > +#endif > + > +/** > + * __rte_may_alias avoids compiler bugs (GCC) that elide > initialization > + * of memory when strict-aliasing is enabled. > + */ > #ifdef RTE_ARCH_STRICT_ALIGN > -typedef uint64_t unaligned_uint64_t __rte_aligned(1); > -typedef uint32_t unaligned_uint32_t __rte_aligned(1); > -typedef uint16_t unaligned_uint16_t __rte_aligned(1); > +typedef uint64_t unaligned_uint64_t __rte_may_alias __rte_aligned(1); > +typedef uint32_t unaligned_uint32_t __rte_may_alias __rte_aligned(1); > +typedef uint16_t unaligned_uint16_t __rte_may_alias __rte_aligned(1); > #else > -typedef uint64_t unaligned_uint64_t; > -typedef uint32_t unaligned_uint32_t; > -typedef uint16_t unaligned_uint16_t; > +typedef uint64_t unaligned_uint64_t __rte_may_alias; > +typedef uint32_t unaligned_uint32_t __rte_may_alias; > +typedef uint16_t unaligned_uint16_t __rte_may_alias; > #endif > > /** > @@ -159,15 +172,6 @@ typedef uint16_t unaligned_uint16_t; > #define __rte_packed_end __attribute__((__packed__)) > #endif > > -/** > - * Macro to mark a type that is not subject to type-based aliasing > rules > - */ > -#ifdef RTE_TOOLCHAIN_MSVC > -#define __rte_may_alias > -#else > -#define __rte_may_alias __attribute__((__may_alias__)) > -#endif > - > /******* Macro to mark functions and fields scheduled for removal > *****/ > #ifdef RTE_TOOLCHAIN_MSVC > #define __rte_deprecated > -- > 2.39.5 (Apple Git-154)
