stddef: Remove token-pasting in TRAILING_OVERLAP()

Browse source

Currently, TRAILING_OVERLAP() token-pastes the FAM parameter into the
name of internal pdding member `__offset_to_##FAM`. This forces FAM to
be a single identifier, which prevents callers from using a FAM when
it's a nested member. For instance, see the following scenario:

| struct flex {
| 	size_t count;
| 	int data[];
| };

| struct foo {
| 	int hdr_foo;
| 	struct flex f;
| };

| struct composite {
| 	struct foo hdr;
| 	int data[100];
| };

In this case, it'd be useful if TRAILING_OVERLAP() could be used in
the following way:

| struct composite {
| 	TRAILING_OVERLAP(struct foo, hdr, f.data,
| 		int data[100];
| 	);
| };

However, this is not current possible due to the token concatenation
in `__offset_to_##FAM`, which fails when FAM contains a dot.

So, remove token-pasting and use the fixed internal name
`__offset_to_FAM` and, with this, expand the capabilities of
TRAILING_OVERLAP(). :)

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/13b3e0a69aad837b4e32ca8269b9d91bf1fbe9ef.1758115257.git.gustavoars@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

...

This commit is contained in:

Gustavo A. R. Silva 2025-09-17 15:26:49 +02:00 • committed by Kees Cook

parent 01c7344e21

commit 413187f790

1 changed files with 1 additions and 1 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

2

include/linux/stddef.h

View file