Speaker
Description
I would like to discuss my ongoing work to supply true
signatures for available functions in kallsyms. The
change will be in clang, pahole, libbpf and kernel.
For clang, the goal is to add additional functions to
dwarf where these functions are not in current dwarf or
their signatures have changed. The example includes like
- original func 'void foo(int a, int b)' becomes
'void foo(int b)', so a new 'void foo(int b)' will
be encoded in dwarf.
- functions like bar.llvm.<hash> at lto mode.
- functions with struct/union arguments and these
arguments will become two (or more?) separate
arguments (e.g., 16 byte struct will become two actual
arguments for x86_64), or become a pointer to the
struct/union.
In pahole, the new functions will be added to vmlinux.BTF.
If an existing func signature changed, add the
signature-changed func to vmlinux.BTF and discard the old one.
The goal is to represent actual function signatures in vmlinux.
With new vmlinux.BTF, we can have true signatures available
to users for fentry etc. We can also handle functions like
bar(...) (in vmlinux.BTF bar.llvm.<hash>) in libbpf properly
(e.g., through regex match etc.). gcc functions like bar.isra,
tar.constprop, etc. can be handled as well if true signature
is available.