[RFC dwarves 0/6] Encoding function addresses using DECL_TAGs

[Alan Maguire <alan.maguire@oracle.com>]

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