| Message ID | 20200317054359.snyyojyf6gjxufij@google.com |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [bpf,v3] bpf: Support llvm-objcopy and llvm-objdump for vmlinux BTF | expand |
On 03/16, Fangrui Song wrote: > On 2020-03-16, Andrii Nakryiko wrote: > > 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 ${1} > > > > > > > >I'm not sure why you are touching this line at all. LLVM_OBJCOPY part > > > >is necessary, pahole assumes llvm-objcopy by default, but that can > > > >(and should for objcopy) be overridden with LLVM_OBJCOPY. > > > > > > Why is LLVM_OBJCOPY assumed? What if llvm-objcopy is not available? > > > > It's pahole assumption that we have to live with. pahole assumes > > llvm-objcopy internally, unless it is overriden with LLVM_OBJCOPY env > > var. So please revert this line otherwise you are breaking it for GCC > > objcopy case. > > Acknowledged. Uploaded v3. > > I added back 2>/dev/null which was removed by a previous change, to > suppress GNU objcopy warnings. The warnings could be annoying in V=1 > output. > > > > This is confusing that one tool assumes llvm-objcopy while the block > > > below immediately uses GNU objcopy (without this patch). > > > > > > e83b9f55448afce3fe1abcd1d10db9584f8042a6 "kbuild: add ability to > > > generate BTF type info for vmlinux" does not say why LLVM_OBJCOPY is > > > set. > > > > > > >> > > > >> - # dump .BTF section into raw binary file to link with final vmlinux > > > >> - bin_arch=$(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 > > > >> > > From ca3597477542453e9f63185c27c162da081a4baf Mon Sep 17 00:00:00 2001 > From: Fangrui Song <maskray@google.com> > Date: Mon, 16 Mar 2020 22:38:23 -0700 > Subject: [PATCH bpf v3] bpf: Support llvm-objcopy and llvm-objdump for > vmlinux BTF > > Simplify gen_btf logic to make it work with llvm-objcopy and llvm-objdump. > Add 2>/dev/null to suppress GNU objcopy (but not llvm-objcopy) warnings > "empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?" > Our use of --only-section drops many SHF_ALLOC sections which will essentially nullify > program headers. When used as linker input, program headers are simply > ignored. > > We use a dd command 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. > Accepting ET_EXEC as an input file is an extremely rare GNU ld feature > that lld does not intend to support, because this is very error-prone. I'm testing this with binutils objcopy, will update with the results. > 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 | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > index dd484e92752e..c3e808a89d4a 100755 > --- a/scripts/link-vmlinux.sh > +++ b/scripts/link-vmlinux.sh > @@ -122,16 +122,8 @@ gen_btf() > vmlinux_link ${1} > LLVM_OBJCOPY=${OBJCOPY} ${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}') Should you also remove 'local bin_arch' on top? > - ${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} ${2} 2> /dev/null && printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 nit: maybe split this into multiple lines? and drop space in '2>/dev/null'? ${OBJCOPY} .... 2>/dev/null && \ printf '\1' | dd .... ?
On 03/16, Fangrui Song wrote: > On 2020-03-16, Andrii Nakryiko wrote: > > 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 ${1} > > > > > > > >I'm not sure why you are touching this line at all. LLVM_OBJCOPY part > > > >is necessary, pahole assumes llvm-objcopy by default, but that can > > > >(and should for objcopy) be overridden with LLVM_OBJCOPY. > > > > > > Why is LLVM_OBJCOPY assumed? What if llvm-objcopy is not available? > > > > It's pahole assumption that we have to live with. pahole assumes > > llvm-objcopy internally, unless it is overriden with LLVM_OBJCOPY env > > var. So please revert this line otherwise you are breaking it for GCC > > objcopy case. > > Acknowledged. Uploaded v3. > > I added back 2>/dev/null which was removed by a previous change, to > suppress GNU objcopy warnings. The warnings could be annoying in V=1 > output. > > > > This is confusing that one tool assumes llvm-objcopy while the block > > > below immediately uses GNU objcopy (without this patch). > > > > > > e83b9f55448afce3fe1abcd1d10db9584f8042a6 "kbuild: add ability to > > > generate BTF type info for vmlinux" does not say why LLVM_OBJCOPY is > > > set. > > > > > > >> > > > >> - # dump .BTF section into raw binary file to link with final vmlinux > > > >> - bin_arch=$(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 > > > >> > > From ca3597477542453e9f63185c27c162da081a4baf Mon Sep 17 00:00:00 2001 > From: Fangrui Song <maskray@google.com> > Date: Mon, 16 Mar 2020 22:38:23 -0700 > Subject: [PATCH bpf v3] bpf: Support llvm-objcopy and llvm-objdump for > vmlinux BTF > > Simplify gen_btf logic to make it work with llvm-objcopy and llvm-objdump. > Add 2>/dev/null to suppress GNU objcopy (but not llvm-objcopy) warnings > "empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?" > Our use of --only-section drops many SHF_ALLOC sections which will essentially nullify > program headers. When used as linker input, program headers are simply > ignored. > > We use a dd command 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. > Accepting ET_EXEC as an input file is an extremely rare GNU ld feature > that lld does not intend to support, because this is very error-prone. > > 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 | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > index dd484e92752e..c3e808a89d4a 100755 > --- a/scripts/link-vmlinux.sh > +++ b/scripts/link-vmlinux.sh > @@ -122,16 +122,8 @@ gen_btf() > vmlinux_link ${1} > LLVM_OBJCOPY=${OBJCOPY} ${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} ${2} 2> /dev/null && printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 No, it doesn't work unfortunately, I get "in-kernel BTF is malformed" from the kernel. I think that's because -O binary adds the following: $ nm .btf.vmxlinux.bin 00000000002f7bc9 D _binary__btf_vmlinux_bin_end 00000000002f7bc9 A _binary__btf_vmlinux_bin_size 0000000000000000 D _binary__btf_vmlinux_bin_start While non-binary mode doesn't: $ nm .btf.vmxlinux.bin We don't add them manually in the linker map and expect objcopy to add them, see: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/kernel/bpf/btf.c#n3480 > } > # 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..c3e808a89d4a 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -122,16 +122,8 @@ gen_btf() vmlinux_link ${1} LLVM_OBJCOPY=${OBJCOPY} ${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} ${2} 2> /dev/null && printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 } # Create ${2} .o file with all symbols from the ${1} object file