From e3251d0a287e1fac7e445ece8afb201512ecf374 Mon Sep 17 00:00:00 2001
From: Douglas Raillard <douglas.raillard@arm.com>
Date: Thu, 2 Jan 2025 11:22:38 +0000
Subject: [PATCH] lisa._btf: Ensure padding members in nested anonymous
 struct/union have unique names

FIX

Nested anonymous struct or union are logically expanded into their
parent struct/union. This means that members of those anonymous types
may clash with the members of a sibling anonymous type. This will never
happen in the original C source (as it would not compile) but we need to
take care when generating synthetic members for padding purpose.

Ensure those padding members are uniquely named by encoding the BTF id
of the anonymous parent(s) they are located in in their name.  Since the
members themselves can be shared at BTF level (thanks to BTF type
deduplication, this can happen), we use the effective parents stack the
type is anonymous type is emitted in.  This way, no clash can happen.
---
 lisa/_btf.py | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/lisa/_btf.py b/lisa/_btf.py
index 44805a31e..9ae24950a 100644
--- a/lisa/_btf.py
+++ b/lisa/_btf.py
@@ -483,12 +483,14 @@ class _BTFStructUnion(_CDecl, BTFType):
             for member in self.members:
                 member._dump_c_introspection(ctx)
 
-    def _do_dump_c_decls(self, ctx, anonymous=False, memoize=True):
+    def _do_dump_c_decls(self, ctx, anonymous=False, memoize=True, parents=None):
         members = self._all_members
         size = self.size
         kind = self._KIND
         name = self.name or ctx.make_name()
         fwd_decl = f'{kind} {name}'
+        _parents = parents or []
+        children_parents = (*_parents, self)
 
         def format_member(member):
             name = member.name
@@ -507,7 +509,7 @@ class _BTFStructUnion(_CDecl, BTFType):
                 # back an internal typedef, which would break the layout of the
                 # parent struct. Anonymous union/struct are only useful if
                 # their declaration are expanded in the parent.
-                return typ._dump_c_decls(ctx, anonymous=True, memoize=False)
+                return typ._dump_c_decls(ctx, anonymous=True, memoize=False, parents=children_parents)
             else:
                 raise ValueError(f'Unsupported anonymous member in {self}')
 
@@ -519,7 +521,7 @@ class _BTFStructUnion(_CDecl, BTFType):
             assert byte_offset >= 0
             return f'_Static_assert(__builtin_offsetof({fwd_decl}, {name}) == {byte_offset}ull, "{fwd_decl}.{name} does not have the expected offset: {byte_offset}")'
 
-        attrs, last_padding = self._align_attribute
+        attrs, last_padding = self._align_attribute(parents=_parents)
         if last_padding:
             members = (*members, last_padding)
         attrs = attrs or ''
@@ -755,8 +757,7 @@ class BTFStruct(_BTFStructUnion):
             else:
                 return alignment
 
-    @property
-    def _align_attribute(self):
+    def _align_attribute(self, parents):
         members = self.members
         size = self.size
         min_alignment = self._min_alignment
@@ -776,13 +777,14 @@ class BTFStruct(_BTFStructUnion):
                 assert size >= min_size
                 last_padding = abs(size - min_size)
 
+                id_ = '_'.join(str(parent.id) for parent in parents)
                 padding = BTFPaddingMember(
                     # The name must be unique inside the struct
                     # (self._index) but also unique among sibling structs,
                     # as ISO C allows anonymous structs inside a top-level
                     # struct, behaving as if their content was inlined in
                     # the parent struct.
-                    name=f'____PADDING_{self.id}_{len(members) + 1}',
+                    name=f'____PADDING_{id_}_{self.id}_{len(members) + 1}',
                     size=last_padding,
                     bit_offset=min_size * 8,
                 )
@@ -812,9 +814,9 @@ class BTFUnion(_BTFStructUnion):
     def alignment(self):
         return self._min_alignment
 
-    @property
-    def _align_attribute(self):
+    def _align_attribute(self, parents):
         size = self.size
+        id_ = '_'.join(str(parent.id) for parent in parents)
         return (
             '__attribute__((packed))' if size % self._min_alignment else None,
             # Always add a padding member in unions since some unions are
@@ -827,7 +829,7 @@ class BTFUnion(_BTFStructUnion):
                 # as ISO C allows anonymous structs inside a top-level
                 # struct, behaving as if their content was inlined in
                 # the parent struct.
-                name=f'__ENSURE_UNION_SIZE_{self.id}_{len(self.members) + 1}',
+                name=f'____ENSURE_UNION_SIZE_{id_}_{self.id}_{len(self.members) + 1}',
                 size=size,
                 bit_offset=0,
             )
-- 
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