Re: [PATCH 00/15] Implement MODVERSIONS for Rust

Masahiro Yamada
2024-06-18T16:51:15Z

On Wed, Jun 19, 2024 at 1:44 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Mon, Jun 17, 2024 at 05:58:19PM +0000, Sami Tolvanen wrote:
> > 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