This patch added the following additional compile-once
run-everywhere (CO-RE) relocations:
- existence/size of typedef, struct/union or enum type
- enum value and enum value existence
These additional relocations will make CO-RE bpf programs more
adaptive for potential kernel internal data structure changes.
For existence/size relocations, the following two code patterns
are supported:
1. uint32_t __builtin_preserve_type_info(*(<type> *)0, flag);
2. <type> var;
uint32_t __builtin_preserve_field_info(var, flag);
flag = 0 for existence relocation and flag = 1 for size relocation.
For enum value existence and enum value relocations, the following code
pattern is supported:
uint64_t __builtin_preserve_enum_value(*(<enum_type> *)<enum_value>,
flag);
flag = 0 means existence relocation and flag = 1 for enum value.
relocation. In the above <enum_type> can be an enum type or
a typedef to enum type. The <enum_value> needs to be an enumerator
value from the same enum type. The return type is uint64_t to
permit potential 64bit enumerator values.
Differential Revision: https://reviews.llvm.org/D83242
Yonghong Song