bpftool incorrectly prints "true" for a false boolean about bpftool HOT 6 CLOSED

Thanks a lot!
Patchwork: https://patchwork.kernel.org/project/netdevbpf/patch/[email protected]/
ML archives: https://lore.kernel.org/all/[email protected]/t/#u

from bpftool.

Thanks for the report!

The raw bytes look right (this is the initial state of the array) but the formatted output is wrong.

Interesting, I wonder what could be the cause. If you have a chance to build locally and run with GDB on your setup, it would be interesting to see what value is passed to jsonw_bool() in btf_dumper_int() (here). Otherwise I'll try to reproduce on my side, but I don't have a 32-bit setup at hand right now.

from bpftool.

Thanks for the pointer! I ran it under gdb and the value passed to jsonw_bool is true. I think the problem is the caller:

	case BTF_INT_BOOL:
		jsonw_bool(jw, *(int *)data);
		break;

The struct layout is:

a: 4 byte
b: 4 byte
c: 2 byte
d: 1 byte
padding: 1 byte

data is a pointer to d so casting to int * and dereference it will read outside the struct boundary right?

from bpftool.

Right, your analysis sounds correct. Have you tried replacing int * with bool *? If it fixes the issue, would you like to submit a patch to the mailing list? I can send one otherwise.

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Making it bool * fixes the issue. I submitted a patch to [email protected] since the change is straightforward but not sure yet how to link it to this issue though.

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Fixed in https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=7184aef9c0f7a81db8fd18d183ee42481d89bf35, well done. I'll pull it here at the next sync.

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