As a means to continue the discussion in [1], which is
concerned with finding the best long-term solution to
having a BPF Type Format (BTF) representation of
functions that is usable for tracing of edge cases, this
proof-of-concept series is intended to explore one approach
to adding information to help make tracing more accurate.
A key problem today is that there is no matching from function
description to the actual instances of a function.
When that function only has one description, that is
not an issue, but if we have multiple inconsistent
static functions in different CUs such as
>From kernel/irq/irqdesc.c
static ssize_t wakeup_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
...and from drivers/base/power/sysfs.c
static ssize_t wakeup_show(struct device *dev, struct device_attribute *attr,
char *buf);
...this becomes a problem. If I am attaching,
which do I want? And even if I know which one
I want, which instance in kallsyms is which?
This series is a proof-of-concept that supports encoding
function addresses and associating them with BTF FUNC
descriptions using BTF declaration tags.
More work would need to be done on the kernel side
to _use_ this representation, but hopefully having a
rough approach outlined will help make that more feasible.
[1] https://lore.kernel.org/bpf/ZF61j8WJls25BYTl@krava/
Alan Maguire (6):
btf_encoder: record function address and if it is local
dwarf_loader: store address in function low_pc if available
dwarf_loader: transfer low_pc info from subtroutine to its abstract
origin
btf_encoder: add "addr=0x<addr>" function declaration tag if
--btf_gen_func_addr specified
btf_encoder: store ELF function representations sorted by name _and_
address
pahole: document --btf_gen_func_addr
btf_encoder.c | 64 +++++++++++++++++++++++++++++++++++-----------
btf_encoder.h | 4 +--
dwarf_loader.c | 16 +++++++++---
dwarves.h | 3 +++
man-pages/pahole.1 | 8 ++++++
pahole.c | 12 +++++++--
6 files changed, 85 insertions(+), 22 deletions(-)
--
2.31.1
