Message ID | 20200317033701.w7jwos7mvfnde2t2@google.com |
---|---|
State | Changes Requested |
Delegated to: | BPF Maintainers |
Headers | show |
Series | [bpf,v2] bpf: Support llvm-objcopy and llvm-objdump for vmlinux BTF | expand |
On Mon, Mar 16, 2020 at 8:37 PM Fangrui Song <maskray@google.com> wrote: > > On 2020-03-16, Andrii Nakryiko wrote: > >On Mon, Mar 16, 2020 at 6:17 PM Fangrui Song <maskray@google.com> 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@google.com> > >> Cc: Nick Desaulniers <ndesaulniers@google.com> > >> Tested-by: Nick Desaulniers <ndesaulniers@google.com> > >> Reported-by: Nathan Chancellor <natechancellor@gmail.com> > >> Link: https://github.com/ClangBuiltLinux/linux/issues/871 > >> Signed-off-by: Fangrui Song <maskray@google.com> > >> --- > >> 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@google.com> > 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@google.com> > Cc: Nick Desaulniers <ndesaulniers@google.com> > Reported-by: Nathan Chancellor <natechancellor@gmail.com> > Link: https://github.com/ClangBuiltLinux/linux/issues/871 > Signed-off-by: Fangrui Song <maskray@google.com> > --- > 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 ${1} I'm not sure why you are touching this line at all. LLVM_OBJCOPY part is necessary, pahole assumes llvm-objcopy by default, but that can (and should for objcopy) be overridden with LLVM_OBJCOPY. > > - # dump .BTF section into raw binary file to link with final vmlinux > - bin_arch=$(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 >
On 2020-03-16, Andrii Nakryiko wrote: >On Mon, Mar 16, 2020 at 8:37 PM Fangrui Song <maskray@google.com> wrote: >> >> On 2020-03-16, Andrii Nakryiko wrote: >> >On Mon, Mar 16, 2020 at 6:17 PM Fangrui Song <maskray@google.com> 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@google.com> >> >> Cc: Nick Desaulniers <ndesaulniers@google.com> >> >> Tested-by: Nick Desaulniers <ndesaulniers@google.com> >> >> Reported-by: Nathan Chancellor <natechancellor@gmail.com> >> >> Link: https://github.com/ClangBuiltLinux/linux/issues/871 >> >> Signed-off-by: Fangrui Song <maskray@google.com> >> >> --- >> >> 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@google.com> >> 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@google.com> >> Cc: Nick Desaulniers <ndesaulniers@google.com> >> Reported-by: Nathan Chancellor <natechancellor@gmail.com> >> Link: https://github.com/ClangBuiltLinux/linux/issues/871 >> Signed-off-by: Fangrui Song <maskray@google.com> >> --- >> 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 ${1} > >I'm not sure why you are touching this line at all. LLVM_OBJCOPY part >is necessary, pahole assumes llvm-objcopy by default, but that can >(and should for objcopy) be overridden with LLVM_OBJCOPY. Why is LLVM_OBJCOPY assumed? What if llvm-objcopy is not available? This is confusing that one tool assumes llvm-objcopy while the block below immediately uses GNU objcopy (without this patch). e83b9f55448afce3fe1abcd1d10db9584f8042a6 "kbuild: add ability to generate BTF type info for vmlinux" does not say why LLVM_OBJCOPY is set. >> >> - # dump .BTF section into raw binary file to link with final vmlinux >> - bin_arch=$(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 >>
On Mon, Mar 16, 2020 at 10:21 PM Fangrui Song <maskray@google.com> wrote: > > > On 2020-03-16, Andrii Nakryiko wrote: > >On Mon, Mar 16, 2020 at 8:37 PM Fangrui Song <maskray@google.com> wrote: > >> > >> On 2020-03-16, Andrii Nakryiko wrote: > >> >On Mon, Mar 16, 2020 at 6:17 PM Fangrui Song <maskray@google.com> 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@google.com> > >> >> Cc: Nick Desaulniers <ndesaulniers@google.com> > >> >> Tested-by: Nick Desaulniers <ndesaulniers@google.com> > >> >> Reported-by: Nathan Chancellor <natechancellor@gmail.com> > >> >> Link: https://github.com/ClangBuiltLinux/linux/issues/871 > >> >> Signed-off-by: Fangrui Song <maskray@google.com> > >> >> --- > >> >> 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@google.com> > >> 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@google.com> > >> Cc: Nick Desaulniers <ndesaulniers@google.com> > >> Reported-by: Nathan Chancellor <natechancellor@gmail.com> > >> Link: https://github.com/ClangBuiltLinux/linux/issues/871 > >> Signed-off-by: Fangrui Song <maskray@google.com> > >> --- > >> 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 ${1} > > > >I'm not sure why you are touching this line at all. LLVM_OBJCOPY part > >is necessary, pahole assumes llvm-objcopy by default, but that can > >(and should for objcopy) be overridden with LLVM_OBJCOPY. > > Why is LLVM_OBJCOPY assumed? What if llvm-objcopy is not available? It's pahole assumption that we have to live with. pahole assumes llvm-objcopy internally, unless it is overriden with LLVM_OBJCOPY env var. So please revert this line otherwise you are breaking it for GCC objcopy case. > This is confusing that one tool assumes llvm-objcopy while the block > below immediately uses GNU objcopy (without this patch). > > e83b9f55448afce3fe1abcd1d10db9584f8042a6 "kbuild: add ability to > generate BTF type info for vmlinux" does not say why LLVM_OBJCOPY is > set. > > >> > >> - # dump .BTF section into raw binary file to link with final vmlinux > >> - bin_arch=$(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 > >>
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