netdev - Re: [PATCH bpf v2] bpf: support pre-2.25-binutils objcopy for vmlinux BTF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <9e43748f-300b-8eb8-fa88-ce5035e5ca83@fb.com>
Date:   Wed, 27 Nov 2019 00:27:05 +0000
From:   Andrii Nakryiko <andriin@...com>
To:     Stanislav Fomichev <sdf@...ichev.me>
CC:     John Fastabend <john.fastabend@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH bpf v2] bpf: support pre-2.25-binutils objcopy for vmlinux
 BTF

On 11/26/19 4:04 PM, Stanislav Fomichev wrote:
> On 11/26, Andrii Nakryiko wrote:
>> On 11/26/19 3:45 PM, Stanislav Fomichev wrote:
>>> On 11/26, John Fastabend wrote:
>>>> Stanislav Fomichev wrote:
>>>>> If vmlinux BTF generation fails, but CONFIG_DEBUG_INFO_BTF is set,
>>>>> .BTF section of vmlinux is empty and kernel will prohibit
>>>>> BPF loading and return "in-kernel BTF is malformed".
>>>>>
>>>>> --dump-section argument to binutils' objcopy was added in version 2.25.
>>>>> When using pre-2.25 binutils, BTF generation silently fails. Convert
>>>>> to --only-section which is present on pre-2.25 binutils.
>>>>>
>>>>> Documentation/process/changes.rst states that binutils 2.21+
>>>>> is supported, not sure those standards apply to BPF subsystem.
>>>>>
>>>>> v2:
>>>>> * exit and print an error if gen_btf fails (John Fastabend)
>>>>>
>>>>> Cc: Andrii Nakryiko <andriin@...com>
>>>>> Cc: John Fastabend <john.fastabend@...il.com>
>>>>> Fixes: 341dfcf8d78ea ("btf: expose BTF info through sysfs")
>>>>> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
>>>>> ---
>>>>>    scripts/link-vmlinux.sh | 7 ++++++-
>>>>>    1 file changed, 6 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
>>>>> index 06495379fcd8..2998ddb323e3 100755
>>>>> --- a/scripts/link-vmlinux.sh
>>>>> +++ b/scripts/link-vmlinux.sh
>>>>> @@ -127,7 +127,8 @@ gen_btf()
>>>>>    		cut -d, -f1 | cut -d' ' -f2)
>>>>>    	bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
>>>>>    		awk '{print $4}')
>>>>> -	${OBJCOPY} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null
>>>>> +	${OBJCOPY} --set-section-flags .BTF=alloc -O binary \
>>>>> +		--only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null
>>>>>    	${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
>>>>>    		--rename-section .data=.BTF .btf.vmlinux.bin ${2}
>>>>>    }
>>>>> @@ -253,6 +254,10 @@ btf_vmlinux_bin_o=""
>>>>>    if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
>>>>>    	if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
>>>>>    		btf_vmlinux_bin_o=.btf.vmlinux.bin.o
>>>>> +	else
>>>>> +		echo >&2 "Failed to generate BTF for vmlinux"
>>>>> +		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
>>>>
>>>> I think we should encourage upgrading binutils first? Maybe
>>>>
>>>> "binutils 2.25+ required for BTF please upgrade or disable CONFIG_DEBUG_INFO_BTF"
>>>>
>>>> otherwise I guess its going to be a bit mystical why it works in
>>>> cases and not others to folks unfamiliar with the details.
>>> With the conversion from --dump-section to --only-section that I
>>> did in this patch, binutils 2.25+ is no longer a requirement.
>>> 2.21 (minimal version from Documentation/process/changes.rst) should work
>>> just fine.
>>
>> Yeah, instead it's better to mention that pahole v1.13+ is required.
> We already have most of the messages about missing pahole or wrong version:
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/scripts/link-vmlinux.sh#n111
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/scripts/link-vmlinux.sh#n117
> 
> They are 'info' though, but it seems logical to drop -s from make arguments
> if someone wants to debug further.
> 

Fair enough. Please add back my Tested-by: tag.

Acked-by: Andrii Nakryiko <andriin@...com>