netdev - Re: [PATCH bpf] libbpf: Sanitise internal map names so they are not rejected by the kernel

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Date:   Tue, 18 Feb 2020 08:19:05 -0800
From:   Yonghong Song <yhs@...com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        <ast@...com>
CC:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf] libbpf: Sanitise internal map names so they are not
 rejected by the kernel



On 2/18/20 6:40 AM, Daniel Borkmann wrote:
> On 2/17/20 6:17 PM, Toke Høiland-Jørgensen wrote:
>> The kernel only accepts map names with alphanumeric characters, 
>> underscores
>> and periods in their name. However, the auto-generated internal map names
>> used by libbpf takes their prefix from the user-supplied BPF object name,
>> which has no such restriction. This can lead to "Invalid argument" errors
>> when trying to load a BPF program using global variables.
>>
>> Fix this by sanitising the map names, replacing any non-allowed 
>> characters
>> with underscores.
>>
>> Fixes: d859900c4c56 ("bpf, libbpf: support global data/bss/rodata 
>> sections")
>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> 
> Makes sense to me, applied, thanks! I presume you had something like '-' 
> in the
> global var leading to rejection?

The C global variable cannot have '-'. I saw a complain in bcc mailing 
list sometimes back like: if an object file is a-b.o, then we will 
generate a map name like a-b.bss for the bss ELF section data. The
map name "a-b.bss" name will be rejected by the kernel. The workaround
is to change object file name. Not sure whether this is the only
issue which may introduce non [a-zA-Z0-9_] or not. But this patch indeed 
should fix the issue I just described.