The existing BTF pruning logic meant that an anonymous struct or
union type hidden behind a typedef, such as in the common construct:
typedef struct { ... } my_struct_type;
could be pruned if 'my_struct_type' was only ever referenced via pointer
members in other structs/unions types used in the program.
The result of pruning is to skip emitting full type information for
a struct or union type by replacing it with a BTF_KIND_FWD, indicating
that it exists but its definition is omitted. Any types used only by
pruned types are fully omitted from the generated BTF.
In cases like this where the struct/union type is anonymous, the result
is an anonymous BTF_KIND_FWD, which is useless. The presence of such a
type record rightly causes complaints from BTF loaders. Worse, since
the TYPEDEF for 'my_struct_type' itself may _not_ be pruned, its type
information will be incomplete.
Change the BTF pruner so that we never consider pruning at a typedef,
and always either keep or discard both the type and the typedef.
Tested on x86_64-linux-gnu and that host for bpf-unknown-none target.
gcc/
* btfout.cc (btf_add_used_type_1): Do not consider creating
fixups at typedefs.
gcc/testsuite/
* gcc.dg/debug/btf/btf-prune-4.c: New.
---
gcc/btfout.cc | 3 +-
gcc/testsuite/gcc.dg/debug/btf/btf-prune-4.c | 61 ++++++++++++++++++++
2 files changed, 63 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-prune-4.c
diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index 5a210cd51e6..eb794ff8694 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -1138,7 +1138,8 @@ btf_add_used_type_1 (ctf_container_ref ctfc,
ctf_dtdef_ref dtd,
/* Try to avoid chasing pointers to struct/union types if the
underlying type isn't used. */
- if (check_ptr && seen_ptr && create_fixups)
+ if (check_ptr && seen_ptr && create_fixups
+ && kind != BTF_KIND_TYPEDEF)
{
ctf_dtdef_ref ref = dtd->ref_type;
uint32_t ref_kind = btf_dtd_kind (ref);
diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-prune-4.c
b/gcc/testsuite/gcc.dg/debug/btf/btf-prune-4.c
new file mode 100644
index 00000000000..9274abf836e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-prune-4.c
@@ -0,0 +1,61 @@
+/* Test that -gprune-btf does not prune at typedefs. */
+
+/* { dg-do compile } */
+/* { dg-options "-gbtf -gprune-btf -dA" } */
+
+/* We must have the full definitions of td1 and td3. Neither are pruned.
+ td2 will be skipped entirely, only because the only reference to
+ it is through struct inner, which is pruned because inner itself
+ is only used as a pointer member.
+
+ In general, we must never get an anonymous FWD; the only FWD in this
+ case will be for 'inner' */
+
+/* Exactly 1 FWD for inner and no anonymous FWD. */
+/* { dg-final { scan-assembler-times "TYPE \[0-9\]+ BTF_KIND_FWD" 1 } } */
+/* { dg-final { scan-assembler-not "TYPE \[0-9\]+ BTF_KIND_FWD ''" } } */
+/* { dg-final { scan-assembler " BTF_KIND_FWD 'inner'" } } */
+
+/* 1 anonymous struct for td1 and 1 anonymous union for td3 */
+/* { dg-final { scan-assembler-times "TYPE \[0-9\]+ BTF_KIND_STRUCT ''" 1 } }
*/
+/* { dg-final { scan-assembler-times "TYPE \[0-9\]+ BTF_KIND_UNION ''" 1 } } */
+
+/* The two remaining typedefs. */
+/* { dg-final { scan-assembler " BTF_KIND_TYPEDEF 'td1'" } } */
+/* { dg-final { scan-assembler " BTF_KIND_TYPEDEF 'td3'" } } */
+
+typedef struct {
+ int x;
+ char c;
+} td1;
+
+typedef struct {
+ long l;
+ char b[4];
+} td2;
+
+typedef union {
+ long l;
+ unsigned short s[2];
+} td3;
+
+struct inner {
+ char a;
+ td2 *ptd;
+ long z;
+};
+
+struct A {
+ td1 *pt;
+ struct inner *in;
+ unsigned long l[4];
+};
+
+struct A foo;
+
+struct B {
+ int x;
+ td3 **ppptd3;
+};
+
+struct B bar;
--
2.51.0
