On Wed, 20 Mar 2024, Qing Zhao wrote:
> + /* This attribute only applies to a C99 flexible array member type. */
> + else if (! c_flexible_array_member_type_p (TREE_TYPE (decl)))
> + {
> + error_at (DECL_SOURCE_LOCATION (decl),
> + "%qE attribute is not allowed for a non"
> + " flexible array member field",
"non-flexible" not "non flexible" ("non" shouldn't appear as a word on its
own).
> + /* Error when the field is not found in the containing structure. */
> + if (!counted_by_field)
> + error_at (DECL_SOURCE_LOCATION (field_decl),
> + "Argument %qE to the %qE attribute is not a field declaration"
> + " in the same structure as %qD", fieldname,
Diagnostics should start with a lowercase letter, "argument" not
"Argument".
> + if (TREE_CODE (TREE_TYPE (real_field)) != INTEGER_TYPE)
> + error_at (DECL_SOURCE_LOCATION (field_decl),
> + "Argument %qE to the %qE attribute is not a field declaration"
> + " with an integer type", fieldname,
Likewise.
Generally checks for integer types should allow any INTEGRAL_TYPE_P,
rather than just INTEGER_TYPE. For example, it should be valid to use
this attribute with a field with _BitInt type. (It would be fairly
useless with a _BitInt larger than size_t, but maybe e.g. someone knows
the size in their code must fit into 24 bits and so uses unsigned
_BitInt(24) for the field.)
Of course there should be corresponding testcases for _Bool / enum /
_BitInt count fields.
What happens when there are multiple counted_by attributes on the same
field? As far as I can see, all but one end up being ignored (by the code
that actually uses the attribute). I think multiple such attributes using
different identifiers should be diagnosed, even if all the identifiers are
indeed integer fields in the same structure - it doesn't seem meaningful
to say that multiple fields give the count of elements. (Multiple
attributes with the *same* identifier are probably OK to allow; maybe that
could arise in code using complicated macros that end up adding the
attribute more than once.)
> +@cindex @code{counted_by} variable attribute
> +@item counted_by (@var{count})
> +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 named "@var{count}" in the same structure as the
> +flexible array member.
You shouldn't use ASCII quotes like that in Texinfo (outside @code etc.
where they represent literal quotes in programming language source code).
You can say ``@var{count}'' if you wish to quote the name.
> +The field that represents the number of the elements should have an
> +integer type. Otherwise, the compiler will report a warning and ignore
> +the attribute.
> +When the field that represents the number of the elements is assigned a
> +negative integer value, the compiler will treat the value as zero.
In general it's best for documentation to be in the present tense (so the
compiler *reports* a warning rather than "will report", *treats* the value
as zero rather than "will treat").
> +It's the user's responsibility to make sure the above requirements to
> +be kept all the time. Otherwise the compiler will report warnings,
> +at the same time, the results of the array bound sanitizer and the
> +@code{__builtin_dynamic_object_size} is undefined.
Likewise.
--
Joseph S. Myers
josmy...@redhat.com
