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Questions - bpf

In "xdp ebpf SEC("tracepoint/xdp/xdp_devmap_xmit")" what is xdp_devmap_xmit -- is this trace means trap handler code start for some kernel function

I have ebpf xdp program with a function with elf section SEC("tracepoint/xdp/xdp_devmap_xmit") I like to know in above is this a hook for which kernel function and what is tracepoint/xdp...
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user786

c

linux

linux-kernel

ebpf

bpf

Votes: 0

Answers: 1

Latest Answer

What does the section name refer to? and what is tracepoint/xdp/xdp_devmap_xmit tracepoint/xdp/xdp_devmap_xmit is the name of the ELF section for this BPF program. The loader (here libbpf) will use ...
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pchaigno

Can struct type be value of bpf hash map?

I want the value in the bpf hash map be a struct, but it doesn't work. who knows if this is allowed by BPF? code like blow. also, I have the second question, how can I call a kernel function in the bp...
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martin bayern

hashmap

ebpf

bpf

Votes: 0

Answers: 1

Latest Answer

Regarding your error: The verifier rejects your program if you try to update the map with uninitialised date from the stack, which is what happens when you create your value. Try to initialise the who...
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Qeole

Need help in XDP program failing to load with error "R7 offset is outside of the packet"

I have written a XDP program that looks at the incoming SCTP packets. A SCTP packets can have multiple chunks into it. I am specifically interested in DATA chunks that contain the application layer pa...
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Pranav Chaudhary

filter

packet

ebpf

bpf

xdp-bpf

Votes: 0

Answers: 1

Latest Answer

TL;DR. You are hitting a corner-case limitation of the verifier. Changing the end of the for loop to the following may help. #define MAX_PACKET_OFF 0xffff ... nh->pos += size; if (nh->pos > M...
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pchaigno

Accessing BPF maps from kernel space

I am beginning with XDP and BPF maps. I understand that to access a BPF map from userspace, we use bpf_* syscalls. For example, bpf_map_lookup_elem() is used to lookup an element of a BPF map in the u...
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diviquery

linux

kernel

ebpf

bpf

xdp-bpf

Votes: 0

Answers: 1

Latest Answer

To lookup map elements from userspace, you should use the bpf(2) syscall, with command BPF_MAP_LOOKUP_ELEM. The main userspace library for BPF does expose this syscall command as bpf_map_lookup_elem()...
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pchaigno

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