> On Aug 5, 2024, at 09:53, Jakub Jelinek <ja...@redhat.com> wrote: > > On Mon, Aug 05, 2024 at 01:33:01PM +0000, Qing Zhao wrote: >> As discussed in >> PR116016:https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116016#c48 >> >> We should explicitly document this limitation and issue error messages for >> C++. >> >> The "counted_by" attribute currently is only supported in C, mention this >> explicitly in documentation and also issue error when see "counted_by" >> attribute in C++. >> >> The patch has been bootstrappped and regression tested on both aarch64 and >> X86, >> no issue. >> >> Okay for committing? >> >> thanks. >> >> Qing >> >> gcc/c-family/ChangeLog: >> >> * c-attribs.cc (handle_counted_by_attribute): Issue error for C++. >> >> gcc/ChangeLog: >> >> * doc/extend.texi: Explicitly mentions counted_by is available >> only for C. >> >> gcc/testsuite/ChangeLog: >> >> * g++.dg/flex-array-counted-by.C: New test. >> --- >> gcc/c-family/c-attribs.cc | 9 ++++++++- >> gcc/doc/extend.texi | 1 + >> gcc/testsuite/g++.dg/flex-array-counted-by.C | 11 +++++++++++ >> 3 files changed, 20 insertions(+), 1 deletion(-) >> create mode 100644 gcc/testsuite/g++.dg/flex-array-counted-by.C >> >> diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc >> index 685f212683f..f936058800b 100644 >> --- a/gcc/c-family/c-attribs.cc >> +++ b/gcc/c-family/c-attribs.cc >> @@ -2859,8 +2859,15 @@ handle_counted_by_attribute (tree *node, tree name, >> tree argval = TREE_VALUE (args); >> tree old_counted_by = lookup_attribute ("counted_by", DECL_ATTRIBUTES >> (decl)); >> >> + /* This attribute is not supported in C++. */ >> + if (c_dialect_cxx ()) >> + { >> + error_at (DECL_SOURCE_LOCATION (decl), >> + "%qE attribute is not supported for C++", name); > > This should be sorry_at instead IMHO (at least if there is a plan to support > it later, hopefully in the 15 timeframe). Okay. > >> + *no_add_attrs = true; >> + } >> /* This attribute only applies to field decls of a structure. */ >> - if (TREE_CODE (decl) != FIELD_DECL) >> + else if (TREE_CODE (decl) != FIELD_DECL) >> { >> error_at (DECL_SOURCE_LOCATION (decl), >> "%qE attribute is not allowed for a non-field" >> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi >> index 48b27ff9f39..f31f3bdb53d 100644 >> --- a/gcc/doc/extend.texi >> +++ b/gcc/doc/extend.texi >> @@ -7848,6 +7848,7 @@ The @code{counted_by} attribute may be attached to the >> C99 flexible array >> member of a structure. It indicates that the number of the elements of the >> array is given by the field "@var{count}" in the same structure as the >> flexible array member. >> +This attribute is available only for C. > > And this should say for now or something similar. Okay. > > > >> GCC may use this information to improve detection of object size information >> for such structures and provide better results in compile-time diagnostics >> and runtime features like the array bound sanitizer and >> diff --git a/gcc/testsuite/g++.dg/flex-array-counted-by.C >> b/gcc/testsuite/g++.dg/flex-array-counted-by.C >> new file mode 100644 >> index 00000000000..7f1a345615e >> --- /dev/null >> +++ b/gcc/testsuite/g++.dg/flex-array-counted-by.C > > Tests shouldn't be added directly to g++.dg/ directory, I think this should > go into g++.dg/ext/ as it is an (unsupported) extension. Makes sense. > >> @@ -0,0 +1,11 @@ >> +/* Testing the fact that the attribute counted_by is not supported in C++. >> */ >> +/* { dg-do compile } */ >> +/* { dg-options "-O2" } */ >> + >> +int size; >> +int x __attribute ((counted_by (size))); /* { dg-error "attribute is not >> supported for C\\+\\+" } */ >> + >> +struct trailing { >> + int count; >> + int field[] __attribute ((counted_by (count))); /* { dg-error "attribute >> is not supported for C\\+\\+" } */ >> +}; > > Maybe it should also test in another { dg-do compile { target c++11 } } test > that the same happens even for [[gnu::counted_by (size)]].
Okay, will add one more test for c++11. > Seems even for C23 there are no tests with [[gnu::counted_by (size)]]. So, you want me to add counted_by test-suite for C23? (Which should be supported) Okay, but I will do it in another separate patch since this patch is for C++. > The C++11/C23 standard attributes are more strict on where they can appear > depending on what it appertains to, as it applies to declarations, I think > it needs to go before the [] or at the start of the declaration, so > [[gnu::counted_by (count)]] int field[]; > or > int field [[gnu::counted_by (count)]] []; > but I could be wrong, better test it… For C++11, as I just checked: int field[] [[gnu::counted_by (count)]]; Is fine. thanks. Qing > > > Jakub
