Re: [PATCH net-next v1] net: stmmac: Drop useless code related to ethtool rx-copybreak

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Jakub Kicinski <kuba@kernel.org>
Date: Wed, 18 Dec 2024 16:42:06 -0800

> On Wed, 18 Dec 2024 16:48:38 +0100 Alexander Lobakin wrote:
>> If sizeof(dma_addr_t) == 8, you're clearly introducing a 4-byte hole
>> here. Perhaps you could reshuffle the struct a bit to avoid this.
>>
>> It's always good to inspect the .kos with pahole after modifying
>> structures to make sure there are no regressions.
> 
> Pretty off topic but I have a dumb question - how do you dump a struct
> with pahole using debug info or BTF from a random .ko?
> Ever since pahole got converted to BTF modules stopped working for me :S

Hmm...

I have this

CONFIG_DEBUG_INFO=y
# CONFIG_DEBUG_INFO_NONE is not set
# CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT is not set
# CONFIG_DEBUG_INFO_DWARF4 is not set
CONFIG_DEBUG_INFO_DWARF5=y
# CONFIG_DEBUG_INFO_REDUCED is not set
# CONFIG_DEBUG_INFO_COMPRESSED_NONE is not set
# CONFIG_DEBUG_INFO_COMPRESSED_ZLIB is not set
CONFIG_DEBUG_INFO_COMPRESSED_ZSTD=y
# CONFIG_DEBUG_INFO_SPLIT is not set
CONFIG_DEBUG_INFO_BTF=y
CONFIG_DEBUG_INFO_BTF_MODULES=y

CONFIG_PAHOLE_VERSION=127
CONFIG_PAHOLE_HAS_SPLIT_BTF=y
CONFIG_PAHOLE_HAS_BTF_TAG=y
CONFIG_PAHOLE_HAS_LANG_EXCLUDE=y

enabled in .config, then I just do

$ pahole path/to/module.ko | less

and search for the struct :D

My pahole is korg Git HEAD.

> I never cared enough to check as most interesting stuff is built-in
> in Meta's kernels but it annoys me every now and then..

Thanks,
Olek