Em Tue, Mar 09, 2021 at 12:59:13AM +0100, Ilya Leoshkevich escreveu:
> Some BPF programs compiled on s390 fail to load, because s390
> arch-specific linux headers contain float and double types.
>
> Fix as follows:
>
> - Make the DWARF loader fill base_type.float_type.
>
> - Introduce libbpf compatibility level command-line parameter, so that
> pahole could be used to build both the older and the newer kernels.
>
> - libbpf introduced the support for the floating-point types in commit
> 986962fade5, so update the libbpf submodule to that version and use
> the new btf__add_float() function in order to emit the floating-point
> types when not in the compatibility mode and base_type.float_type is
> set.
>
> - Make the BTF loader recognize the new BTF kind.
>
> Example of the resulting entry in the vmlinux BTF:
>
> [7164] FLOAT 'double' size=8
>
> when building with:
>
> LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} --libbpf_compat=0.4.0
I'm testing it now, and added as a followup patch the man page entry,
please check that the wording is appropriate.
Thanks,
- Arnaldo
[acme@five pahole]$ vim man-pages/pahole.1
[acme@five pahole]$ git diff
diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index 352bb5e45f319da4..787771753d1933b1 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -199,6 +199,12 @@ Path to the base BTF file, for instance: vmlinux when encoding kernel module BTF
This may be inferred when asking for a /sys/kernel/btf/MODULE, when it will be autoconfigured
to "/sys/kernel/btf/vmlinux".
+.TP
+.B \-\-libbpf_compat=LIBBPF_VERSION
+Produce output compatible with this libbpf version. For instance, specifying 0.4.0 as
+the version would encode BTF_KIND_FLOAT entries in systems where the vmlinux DWARF
+information has float types.
+
.TP
.B \-l, \-\-show_first_biggest_size_base_type_member
Show first biggest size base_type member.
[acme@five pahole]$
