netdev - Re: [PATCH net-next v7 2/5] rust: net::phy add module_phy

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Message-ID: <7f300ba1-44e1-4a98-9289-a53928204aa7@proton.me>
Date: Fri, 17 Nov 2023 23:01:58 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Andrew Lunn <andrew@...n.ch>, Boqun Feng <boqun.feng@...il.com>
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>, netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, tmgross@...ch.edu, miguel.ojeda.sandonis@...il.com, wedsonaf@...il.com
Subject: Re: [PATCH net-next v7 2/5] rust: net::phy add module_phy_driver macro

On 11/17/23 23:54, Andrew Lunn wrote:
> Each kernel module should be in its own symbol name space. The only
> symbols which are visible outside of the module are those exported
> using EXPORT_SYMBOL_GPL() or EXPORT_SYMBOL(). A PHY driver does not
> export anything, in general.
> 
> Being built in also does not change this.
> 
> Neither drivers/net/phy/ax88796b_rust.o nor
> rust/doctests_kernel_generated.o should have exported this symbol.
> 
> I've no idea how this actually works, i guess there are multiple
> passes through the linker? Maybe once to resolve symbols across object
> files within a module. Normal global symbols are then made local,
> leaving only those exported with EXPORT_SYMBOL_GPL() or
> EXPORT_SYMBOL()? A second pass through linker then links all the
> exported symbols thorough the kernel?

I brought this issue up in [1], but I was a bit confused by your last
reply there, as I have no idea how the `EXPORT_SYMBOL` macros work.

IIRC on the Rust side all public items are automatically GPL exported.
But `#[no_mangle]` is probably a special case, since in userspace it
is usually used to do interop with C (and therefore the symbol is always
exported with the name not mangled).

One fix would be to make the name unique by using the type name supplied
in the macro.

[1]: https://lore.kernel.org/rust-for-linux/1aea7ddb-73b7-8228-161e-e2e4ff5bc98d@proton.me/

-- 
Cheers,
Benno