On 2/18/20 5:42 PM, Toke Høiland-Jørgensen wrote:

Yonghong Song [off-list ref] writes:

quoted

On 2/18/20 6:40 AM, Daniel Borkmann wrote:

quoted

On 2/17/20 6:17 PM, Toke Høiland-Jørgensen wrote:

quoted

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 <redacted>

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.

Yep, meant object file name, just realized too late after sending. :/

Yes, this was exactly my problem; my object file is called
'xdp-dispatcher.o'. Fun error to track down :P

Why doesn't the kernel allow dashes in the name anyway?

Commit cb4d2b3f03d8 ("bpf: Add name, load_time, uid and map_ids to bpf_prog_info")
doesn't state a specific reason, and we did later extend it via 3e0ddc4f3ff1 ("bpf:
allow . char as part of the object name"). My best guess right now is potentially
not to confuse BPF's kallsyms handling with dashes etc.