On 2020-03-16, Andrii Nakryiko wrote:
On Mon, Mar 16, 2020 at 6:17 PM Fangrui Song <maskray@xxxxxxxxxx> wrote:
Simplify gen_btf logic to make it work with llvm-objcopy and
llvm-objdump. We just need to retain one section .BTF. To do so, we can
use a simple objcopy --only-section=.BTF instead of jumping all the
hoops via an architecture-less binary file.
We use a dd comment to change the e_type field in the ELF header from
ET_EXEC to ET_REL so that .btf.vmlinux.bin.o will be accepted by lld.
Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux")
Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/871
Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx>
---
scripts/link-vmlinux.sh | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index dd484e92752e..84be8d7c361d 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -120,18 +120,9 @@ gen_btf()
info "BTF" ${2}
vmlinux_link ${1}
- LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
Is it really tested? Seems like you just dropped .BTF generation step
completely...
Sorry, dropped the whole line:/
I don't know how to test .BTF . I can only check readelf -S...
Attached the new patch.
From 02afb9417d4f0f8d2175c94fc3797a94a95cc248 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@xxxxxxxxxx>
Date: Mon, 16 Mar 2020 18:02:31 -0700
Subject: [PATCH bpf v2] bpf: Support llvm-objcopy and llvm-objdump for
vmlinux BTF
Simplify gen_btf logic to make it work with llvm-objcopy and llvm-objdump.
We use a dd comment to change the e_type field in the ELF header from
ET_EXEC to ET_REL so that .btf.vmlinux.bin.o can be accepted by lld.
Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux")
Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/871
Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx>
---
scripts/link-vmlinux.sh | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index dd484e92752e..b23313944c89 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -120,18 +120,10 @@ gen_btf()
info "BTF" ${2}
vmlinux_link ${1}
- LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
+ ${PAHOLE} -J ${1}
- # dump .BTF section into raw binary file to link with final vmlinux
- bin_arch=$(LANG=C ${OBJDUMP} -f ${1} | grep architecture | \
- cut -d, -f1 | cut -d' ' -f2)
- bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
- awk '{print $4}')
- ${OBJCOPY} --change-section-address .BTF=0 \
- --set-section-flags .BTF=alloc -O binary \
- --only-section=.BTF ${1} .btf.vmlinux.bin
- ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
- --rename-section .data=.BTF .btf.vmlinux.bin ${2}
+ # Extract .BTF section, change e_type to ET_REL, to link with final vmlinux
+ ${OBJCOPY} --only-section=.BTF ${1} ${2} && printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16
}
# Create ${2} .o file with all symbols from the ${1} object file
--
2.25.1.481.gfbce0eb801-goog
