[Clang][counted_by] Add support for 'counted_by' on struct pointers #137250
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The 'counted_by' attribute is now available for structs. It generates
code for sanity checks as well as __builtin_dynamic_object_size()
calculations. For example:
struct annotated_ptr {
int count;
void *buf __attribute__((counted_by(count)));
};
The attribute can be applied to a 'void *'. In that case, use the
'sized_by' attribute instead:
struct annotated_ptr {
void *buf __attribute__((sized_by(count)));
size_t count;
};
The 'count' field member may occur after the pointer. If it does, use
the '-fexperimental-late-parse-attributes' flag (which will hopefully be
made the default in future Clang versions).
Note that 'counted_by' cannot be applied to a pointer to an incomplete
type, because the size isn't known.
struct foo;
struct annotated_ptr {
int count;
struct foo *buf __attribute__((counted_by(count))); /* invalid */
};
Signed-off-by: Bill Wendling <[email protected]>
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✅ With the latest revision this PR passed the C/C++ code formatter. |
… redundant 'isCounteAttributedType'.
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This is looking good, but needs to support |
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Friendly ping. :-) |
AaronBallman
reviewed
May 1, 2025
There was a problem hiding this comment.
I think the changes look reasonable but I'd appreciate final sign-off from @efriedma-quic or @rjmccall given this is all codegen work.
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Friendly ping x 2 :) |
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The 'counted_by' attribute is now available for pointers in structs.
It generates code for sanity checks as well as __builtin_dynamic_object_size()
calculations. For example:
struct annotated_ptr {
int count;
char *buf attribute((counted_by(count)));
};
If the pointer's type is 'void *', use the 'sized_by' attribute, which
works similarly to 'counted_by', but can handle the 'void' base type:
struct annotated_ptr {
int count;
void *buf attribute((sized_by(count)));
};
If the 'count' field member occurs after the pointer, use the
'-fexperimental-late-parse-attributes' flag during compilation.
Note that 'counted_by' cannot be applied to a pointer to an incomplete
type, because the size isn't known.
struct foo;
struct annotated_ptr {
int count;
struct foo buf attribute((counted_by(count))); / invalid */
};
Signed-off-by: Bill Wendling [email protected]