ANNOUNCE: pahole v1.21 (clang's LTO edition, BTF floats)

Arnaldo Carvalho de Melo
2021-04-12T15:08:17Z

Hi,

The v1.21 release of pahole and its friends is out, this time it's
about using clang to build the kernel with LTO, some DWARF5 fixes, supporting
floating types in the BTF encoder for s/390 sake and some misc fixes and
improvements. Ah, it should also be faster due to switching to using libbpf's
hashing routines.

Main git repo:

git://git.kernel.org/pub/scm/devel/pahole/pahole.git

Mirror git repo:

https://github.com/acmel/dwarves.git

tarball + gpg signature:

https://fedorapeople.org/~acme/dwarves/dwarves-1.21.tar.xz
https://fedorapeople.org/~acme/dwarves/dwarves-1.21.tar.bz2
https://fedorapeople.org/~acme/dwarves/dwarves-1.21.tar.sign

Thanks a lot to all the contributors and distro packagers, you're on the
CC list, I appreciate a lot the work you put into these tools,

Best Regards,

- Arnaldo

DWARF loader:

- Handle DWARF5 DW_OP_addrx properly

Part of the effort to support the subset of DWARF5 that is generated when building the kernel.

- Handle subprogram ret type with abstract_origin properly

Adds a second pass to resolve abstract origin DWARF description of functions to aid
the BTF encoder in getting the right return type.

- Check .notes section for LTO build info

When LTO is used, currently only with clang, we need to do extra steps to handle references
from one object (compile unit, aka CU) to another, a way for DWARF to avoid duplicating
information.

- Check .debug_abbrev for cross-CU references

When the kernel build process doesn't add an ELF note in vmlinux indicating that LTO was
used and thus intra-CU references are present and thus we need to use a more expensive
way to resolve types and (again) thus to encode BTF, we need to look at DWARF's .debug_abbrev
ELF section to figure out if such intra-CU references are present.

- Permit merging all DWARF CU's for clang LTO built binary

Allow not trowing away previously supposedly self contained compile units
(objects, aka CU, aka Compile Units) as they have type descriptions that will
be used in later CUs.

- Permit a flexible HASHTAGS__BITS

So that we can use a more expensive algorithm when we need to keep previously processed
compile units that will then be referenced by later ones to resolve types.

- Use a better hashing function, from libbpf

Enabling patch to combine compile units when using LTO.

BTF encoder:

- Add --btf_gen_all flag

A new command line to allow asking for the generation of all BTF encodings, so that we
can stop adding new command line options to enable new encodings in the kernel Makefile.

- Match ftrace addresses within ELF functions

To cope with differences in how DWARF and ftrace describes function boundaries.

- Funnel ELF error reporting through a macro

To use libelf's elf_error() function, improving error messages.

- Sanitize non-regular int base type

Cope with clang with dwarf5 non-regular int base types, tricky stuff, see yhs
full explanation in the relevant cset.

- Add support for the floating-point types

S/390 has floats'n'doubles in its arch specific linux headers, cope with that.

Pretty printer:

- Honour conf_fprintf.hex when printing enumerations

If the user specifies --hex in the command line, honour it when printing enumerations.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>