https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125888
Bug ID: 125888
Summary: btf_type_tag for types not supported for defined
struct
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: vineetg at gcc dot gnu.org
CC: dfaust at gcc dot gnu.org, jemarch at gcc dot gnu.org
Target Milestone: ---
This was brought up by Emil@meta and seems like a legit feature request.
For an existing generic kernel structure, users might want to define a
specialized type with a custom btf_type_tag attached, e.g.
```
typedef struct rbtree __arena rbtree_t;
```
Currently gcc ignores this and emits -Wattributes warning
test.c:7:16: warning: ignoring attributes applied to ‘struct rbtree’ after
definition [-Wattributes]
The workaround is to specify struct def when creating the type which obviously
doesn't work for existing structs in kernel headers.
FWIW independent of this request - when enabling decl/type tags in Linux kernel
with gcc 16+ (containing decl gcc tag support from David) we get a lot of build
spew for percpu variables.
```
struct cpuinfo_x86 {
unsigned initialized;
};
extern __attribute__((btf_type_tag("percpu")))
__attribute__((section(".data..percpu" "..read_mostly")))
__typeof__(struct cpuinfo_x86) cpu_info;
```
