bpf: Generate BTF_KIND_FLOAT when linking vmlinux

mainline inclusion
from mainline-5.13-rc1
commit db16c1fe
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=db16c1fe92d7ba7d39061faef897842baee2c887

-------------------------------------------------

pahole v1.21 supports the --btf_gen_floats flag, which makes it
generate the information about the floating-point types [1].

Adjust link-vmlinux.sh to pass this flag to pahole in case it's
supported, which is determined using a simple version check.

[1] https://lore.kernel.org/dwarves/YHRiXNX1JUF2Az0A@kernel.org/Signed-off-by: NIlya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: NAndrii Nakryiko <andrii@kernel.org>
Acked-by: NAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210413190043.21918-1-iii@linux.ibm.com
(cherry picked from commit db16c1fe)
Signed-off-by: NWang Yufen <wangyufen@huawei.com>

scripts/link-vmlinux.sh

@@ -140,6 +140,7 @@ vmlinux_link()
 gen_btf()
 {
 	local pahole_ver
+	local extra_paholeopt=
 
 	if ! [ -x "$(command -v ${PAHOLE})" ]; then
 		echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
@@ -154,8 +155,12 @@ gen_btf()
 
 	vmlinux_link ${1}
 
+	if [ "${pahole_ver}" -ge "121" ]; then
+		extra_paholeopt="${extra_paholeopt} --btf_gen_floats"
+	fi
+
 	info "BTF" ${2}
-	LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
+	LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${extra_paholeopt} ${1}
 
 	# Create ${2} which contains just .BTF section but no symbols. Add
 	# SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all