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From: Eric Botcazou <ebotcazou@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-1072] Warn on type punning that toggles scalar storage order Date: Wed, 26 May 2021 17:14:05 +0000 (GMT) [thread overview] Message-ID: <20210526171405.7BDF23858004@sourceware.org> (raw) https://gcc.gnu.org/g:401bd4adcfda9965363b1ac3ba7e1580f15d6883 commit r12-1072-g401bd4adcfda9965363b1ac3ba7e1580f15d6883 Author: Eric Botcazou <ebotcazou@adacore.com> Date: Wed May 26 19:12:05 2021 +0200 Warn on type punning that toggles scalar storage order As documented in the manual, we do not support type punning that toggles the scalar storage order, so this adds a warning for the case of unions. gcc/c/ PR c/100653 * c-decl.c (finish_struct): Warn for a union containing an aggregate field with a differing scalar storage order. gcc/testsuite/ * gcc.dg/sso-13.c: New test. Diff: --- gcc/c/c-decl.c | 7 +++++++ gcc/testsuite/gcc.dg/sso-13.c | 24 ++++++++++++++++++++++++ 2 files changed, 31 insertions(+) diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c index 53b2b5b637d..3c7b306809d 100644 --- a/gcc/c/c-decl.c +++ b/gcc/c/c-decl.c @@ -8853,6 +8853,13 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes, = c_build_qualified_type (fmain_type, TYPE_QUALS (ftype)); } } + + if (TREE_CODE (t) == UNION_TYPE + && AGGREGATE_TYPE_P (TREE_TYPE (field)) + && TYPE_REVERSE_STORAGE_ORDER (t) + != TYPE_REVERSE_STORAGE_ORDER (TREE_TYPE (field))) + warning_at (DECL_SOURCE_LOCATION (field), OPT_Wscalar_storage_order, + "type punning toggles scalar storage order"); } /* Now we have the truly final field list. diff --git a/gcc/testsuite/gcc.dg/sso-13.c b/gcc/testsuite/gcc.dg/sso-13.c new file mode 100644 index 00000000000..ddfde00b758 --- /dev/null +++ b/gcc/testsuite/gcc.dg/sso-13.c @@ -0,0 +1,24 @@ +/* Test support of scalar_storage_order attribute */ + +/* { dg-do compile } */ + +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ +#define REV_ENDIANNESS __attribute__((scalar_storage_order("big-endian"))) +#else +#define REV_ENDIANNESS __attribute__((scalar_storage_order("little-endian"))) +#endif + +typedef struct tIp6Addr +{ + unsigned int s6_addr32[4]; +} tIp6Addr; + +struct _tBeTimNetAddr +{ + unsigned char isIPv4; + union + { + unsigned int addr; + tIp6Addr addr6; /* { dg-warning "type punning toggles" } */ + } REV_ENDIANNESS u; +} REV_ENDIANNESS;
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