On Wed, Jun 19, 2024 at 1:44 AM Greg Kroah-Hartman
[off-list ref] wrote:

On Mon, Jun 17, 2024 at 05:58:19PM +0000, Sami Tolvanen wrote:

quoted

Hi folks,

This series implements CONFIG_MODVERSIONS for Rust, an important
feature for distributions like Android that want to ship Rust
kernel modules, and depend on modversions to help ensure module ABI
compatibility.

There have been earlier proposals [1][2] that would allow Rust
modules to coexist with modversions, but none that actually implement
symbol versioning. Unlike C, Rust source code doesn't have sufficient
information about the final ABI, as the compiler has considerable
freedom in adjusting structure layout for improved performance [3],
for example, which makes using a source code parser like genksyms
a non-starter. Based on Matt's suggestion and previous feedback
from maintainers, this series uses DWARF debugging information for
computing versions. DWARF is an established and relatively stable
format, which includes all the necessary ABI details, and adding a
CONFIG_DEBUG_INFO dependency for Rust symbol versioning seems like a
reasonable trade-off.

The first 12 patches of this series add a small tool for computing
symbol versions from DWARF, called gendwarfksyms. When passed a list
of exported symbols, the tool generates an expanded type string
for each symbol, and computes symbol CRCs similarly to genksyms.
gendwarfksyms is written in C and uses libdw to process DWARF, mainly
because of the existing support for C host tools that use elfutils
(e.g., objtool).

That's cool, can the C code be switched to also use this?  That way we
only have one path/code for all of this?

As the description says, it requires CONFIG_DEBUG_INFO.
We can strip the debug info from the final vmlinux, but
I guess the build speed will be even slower than the current genksyms.




-- 
Best Regards
Masahiro Yamada