On Fri, 11 Oct 2024 22:38:53 +0800 Zheng Yejian zhengyejian@huaweicloud.com wrote:

Currently when the length of a symbol is longer than 0x7f characters, its type shown in /proc/kallsyms can be incorrect.

I found this issue when reading the code, but it can be reproduced by following steps:

1. Define a function which symbol length is 130 characters:

#define X13(x) x##x##x##x##x##x##x##x##x##x##x##x##x static noinline void X13(x123456789)(void) { printk("hello world\n"); }

2. The type in vmlinux is 't':

$ nm vmlinux | grep x123456 ffffffff816290f0 t x123456789x123456789x123456789x12[...]

3. Then boot the kernel, the type shown in /proc/kallsyms becomes 'g'

instead of the expected 't':

# cat /proc/kallsyms | grep x123456 ffffffff816290f0 g x123456789x123456789x123456789x12[...]

The root cause is that, after commit 73bbb94466fd ("kallsyms: support "big" kernel symbols"), ULEB128 was used to encode symbol name length. That is, for "big" kernel symbols of which name length is longer than 0x7f characters, the length info is encoded into 2 bytes.

kallsyms_get_symbol_type() expects to read the first char of the symbol name which indicates the symbol type. However, due to the "big" symbol case not being handled, the symbol type read from /proc/kallsyms may be wrong, so handle it properly.

Cc: stable@vger.kernel.org Fixes: 73bbb94466fd ("kallsyms: support "big" kernel symbols") Signed-off-by: Zheng Yejian zhengyejian@huaweicloud.com

Gary made me aware of this thread (thanks!) -- we are coming from:

https://lore.kernel.org/all/aQjua6zkEHYNVN3X@x1/

For which I sent this patch without knowing about this one:

https://lore.kernel.org/rust-for-linux/20251107050414.511648-1-ojeda@kernel....

This has been seen now by Arnaldo (Cc'ing) in a real system, so I think we should take this one since it was first, with:

Cc: stable@vger.kernel.org

Thanks!

Cheers, Miguel