[PATCH v2] handle qualified anonymous structures

[PATCH v2] handle qualified anonymous structures

[Luc Van Oostenryck]

The kernel is trying to use a unnamed struct to mark a group of
fields as being 'const' and get a warning if one of its member is
assigned. GCC gives indeed a warning but Sparse and clang don't.

So, the type qualifiers of the anonymous struct need to be propagate
to the members.

An easy, one-liner, solution is to handle this inside find_identifier(),
where access to the members are recursively searched inside sub-structures.
It's very easy but it feels wrong to do semantics inside this function.
Worse, it's only working for members that are effectively accessed,
doing a type evaluation on the anonymous struct (or its parent)
would, by itself, not handle this.

So, the solution chosen here is to handle this during type examination,
more precisely, inside examine_struct_union_type(), where things are
a bit more complicated (it can't be done when examining the members
themselves because only the parent SYM_STRUCT is accessible and the
qualifiers are in the SYM_NODE, so it needs to be done when examining
the anonymous struct itself) but can be done for all members.

Note: It would seem logical to also handle at least all qualifier-like
      attributes but GCC seems to only bother with the true qualifiers
      and ignore things like attributes and alignment specifiers.

Link: lore.kernel.org/r/CAHk-=wj4Kviw8q2Sx9vrrvyn3uWK-zNi4uGRx=5bzde0Cio8uQ@mail.gmail.com
Link: lore.kernel.org/r/CAHk-=wjdJmL22+zk3_rWAfEJJCf=oDxiJ530qk-WNk_Ji0qhxw@mail.gmail.com
Thanks-to: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---

Change since v1:
* factor out the modifiers from the 'sub' loop
* remove the sym-vs-parent thing thanks to the previous point
* check that sub-members are always a SYM_NODE (via an assert, sorry)

 symbol.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/symbol.c b/symbol.c
index aa02c8c5ad80..91352a3a447b 100644
--- a/symbol.c
+++ b/symbol.c
@@ -25,6 +25,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <assert.h>
 
 #include "lib.h"
 #include "allocate.h"
@@ -175,6 +176,31 @@ static void lay_out_struct(struct symbol *sym, struct struct_union_info *info)
 	// warning (sym->pos, "regular: offset=%d", sym->offset);
 }
 
+///
+// propagate properties of anonymous structs or unions into their members.
+//
+// :note: GCC seems to only propagate the qualifiers.
+// :note: clang doesn't propagate anything at all.
+static void examine_anonymous_member(struct symbol *sym)
+{
+	unsigned long mod = sym->ctype.modifiers & MOD_QUALIFIER;
+	struct symbol *sub;
+
+	if (sym->type == SYM_NODE)
+		sym = sym->ctype.base_type;
+	if (sym->type != SYM_STRUCT && sym->type != SYM_UNION)
+		return;
+
+	FOR_EACH_PTR(sym->symbol_list, sub) {
+		assert(sub->type == SYM_NODE);
+		sub->ctype.modifiers |= mod;
+
+		// if nested, propagate all the way down
+		if (!sub->ident)
+			examine_anonymous_member(sub);
+	} END_FOR_EACH_PTR(sub);
+}
+
 static struct symbol * examine_struct_union_type(struct symbol *sym, int advance)
 {
 	struct struct_union_info info = {
@@ -196,6 +222,8 @@ static struct symbol * examine_struct_union_type(struct symbol *sym, int advance
 		if (info.flex_array)
 			sparse_error(info.flex_array->pos, "flexible array member '%s' is not last", show_ident(info.flex_array->ident));
 		examine_symbol_type(member);
+		if (!member->ident)
+			examine_anonymous_member(member);
 
 		if (member->ctype.alignment > info.max_align && !sym->packed) {
 			// Unnamed bitfields do not affect alignment.
-- 
2.30.0