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Message-ID: <20250401155735.GA804471@joelnvbox>
Date: Tue, 1 Apr 2025 11:57:35 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Guangbo Cui <2407018371@...com>, Miguel Ojeda <ojeda@...nel.org>,
a.hindborg@...nel.org, alex.gaynor@...il.com, aliceryhl@...gle.com,
benno.lossin@...ton.me, bjorn3_gh@...tonmail.mco,
boqun.feng@...il.com, boris.brezillon@...labora.com,
dakr@...nel.org, gary@...yguo.net, gregkh@...uxfoundation.org,
linux-kernel@...r.kernel.org, rafael@...nel.org, robh@...nel.org,
rust-for-linux@...r.kernel.org, tmgross@...ch.edu,
John Hubbard <jhubbard@...dia.com>,
Alexandre Courbot <acourbot@...dia.com>,
Alistair Popple <apopple@...dia.com>
Subject: Re: [PATCH v6 2/3] rust: io: mem: add a generic iomem abstraction
On Thu, Feb 06, 2025 at 12:57:30PM -0300, Daniel Almeida wrote:
> Btw, Miguel & others,
>
> IMHO, I think we should write a comment about this somewhere in the docs.
>
> When I first came across this issue myself, it took me a while to understand that
> the build_error was actually triggering.
>
> That’s because the result is:
>
> ```
> ERROR: modpost: "rust_build_error" [rust_platform_uio_driver.ko] undefined!
> ```
>
> When a symbol is undefined, someone would be within their rights to assume that
> something is broken in some KConfig somewhere, like this person did. It specifically
> doesn’t tell them that the problem is their own code triggering a build_error because
> they are misusing an API.
>
> I know that we can’t really provide a message through build_error itself, hence my
> suggestion about the docs.
>
> I can send a patch if you agree, it will prevent this confusion from coming up in the
> future.
Interesting, I just ran into this. I am writing function as follows that
reads bar0 in the nova driver, however not having the "if current_len + i"
causes the same issue:
ERROR: modpost: "rust_build_error" [nova_core.ko] undefined!
which did not help much about what the issue really is. I had to figure it
out through tedious trial and error. Also what is the reason for this, the
compiler is doing some checks in with_bar? Looking at with_bar
implementation, I could not see any. Also enabling
CONFIG_RUST_BUILD_ASSERT_ALLOW did not show more menaingful messages. Thanks
for taking a look:
pub(crate) fn read_more(&mut self, bytes: u32) -> Result {
with_bar!(self.bar0, |bar0| {
// Get current length
let current_len = self.data.len();
// Read ROM data bytes push directly to vector
for i in 0..bytes as usize {
// This check fixes:
// ERROR: modpost: "rust_build_error" [nova_core.ko] undefined!
if current_len + i >= 10000000 {
return Err(EINVAL);
}
// Read a byte from the VBIOS ROM and push it to the data vector
let rom_addr = ROM_OFFSET + current_len + i;
let byte = bar0.readb(rom_addr);
self.data.push(byte, GFP_KERNEL)?;
}
Ok(())
})?
}
thanks,
- Joel
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