On Tue, Sep 29, 2020 at 09:27:31PM -0700, Andrii Nakryiko wrote:
> This patch set switches pahole to use libbpf-provided BTF loading and encoding
> APIs. This reduces pahole's own BTF encoding code, speeds up the process,
> reduces amount of RAM needed for DWARF-to-BTF conversion. Also, pahole finally
> gets support to generating BTF for cross-compiled ELF binaries with different
> endianness (patch #11).
>
Hello Andrii,
After a small hiccup (see below) I managed to build a modified 'pahole' and test
cross-compiling from x86_64 to mips 64/32-bit and big/little-endian
targets. Using
"bpftool btf dump file /sys/kernel/btf/vmlinux format c" succeeded on
all targets,
whereas prior to your changes running on big-endian targets would
raise an error.
(Note that the 'bpftool' used a 'libbpf' without any of your changes.)
Thanks so much for tackling these BTF endianness problems; it's been a great
help for working with embedded systems.
> Additionally, patch #6 fixes previously missed problem with invalid array
> index type generation.
>
> Patches #7-10 are speeding up DWARF-to-BTF convertion/dedup pretty
> significantly, saving overall about 9 seconds out of current 27 or so.
>
> Patch #8 revamps how per-CPU BTF variables are emitted, eliminating repeated
> and expensive looping over ELF symbols table.
>
> Patch #10 admittedly has some hacky parts to satisfy CTF use case, but its
> speed ups are greatest. So I'll understand if it gets dropped, but it would be
> a pity.
>
Possibly a case of operator error, but I had to skip this patch to
cleanly build 'pahole',
and didn't have much chance to look into the compile error:
[ 1%] Building C object CMakeFiles/bpf.dir/lib/bpf/src/ringbuf.c.o
In file included from /home/kodidev/pahole/strings.h:9,
from /usr/include/string.h:432,
from /home/kodidev/pahole/lib/bpf/src/libbpf_common.h:12,
from /home/kodidev/pahole/lib/bpf/src/libbpf.h:20,
from /home/kodidev/pahole/lib/bpf/src/ringbuf.c:20:
/home/kodidev/pahole/lib/bpf/src/btf.h:33:11: error: expected ‘;’
before ‘void’
33 | LIBBPF_API void btf__free(struct btf *btf);
| ^~~~~
| ;
Kind regards,
Tony
> More details could be found in respective patches.
>
> Andrii Nakryiko (11):
> libbpf: update to latest libbpf version
> btf_encoder: detect BTF encoding errors and exit
> dwarves: expose and maintain active debug info loader operations
> btf_loader: use libbpf to load BTF
> btf_encoder: use libbpf APIs to encode BTF type info
> btf_encoder: fix emitting __ARRAY_SIZE_TYPE__ as index range type
> btf_encoder: discard CUs after BTF encoding
> btf_encoder: revamp how per-CPU variables are encoded
> dwarf_loader: increase the size of lookup hash map
> strings: use BTF's string APIs for strings management
> btf_encoder: support cross-compiled ELF binaries with different
> endianness
>
