undefined reference to `__sheap'

[Christopher Hunt]

When linking my library with the following:

    unsafe { ALLOCATOR.init(cortex_m_rt::heap_start() as usize, HEAP_SIZE_BYTES) }

I receive a:

undefined reference to `__sheap'

I didn't find a documented means by which this symbol is declared. Any pointers? I'm linking my Rust library to an nRF52 C based project. Thanks.

[Thales]

Do you have this line on your .cargo/config ?

https://github.com/rust-embedded/cortex-m-quickstart/blob/3cbcb9956acd638c0fb864937770f51d663fba6f/.cargo/config#L18

[Christopher Hunt]

I don’t have that line. Also, I’m using the gcc linker so I might have to read up on those options. Is there a section in the doc discussing the need for these options? Happy to PR the doc once I learn more if not. Thanks.

…

On 15 Oct 2020, at 00:46, Thales ***@***.***> wrote:  Do you have this line on your .cargo/config ? https://github.com/rust-embedded/cortex-m-quickstart/blob/3cbcb9956acd638c0fb864937770f51d663fba6f/.cargo/config#L18 — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or unsubscribe.

[Christopher Hunt]

Unfortunately, that line, or a combo of the other lines doesn’t help to resolve the symbol.

…

On 15 Oct 2020, at 12:46 am, Thales ***@***.***> wrote: Do you have this line on your .cargo/config ? https://github.com/rust-embedded/cortex-m-quickstart/blob/3cbcb9956acd638c0fb864937770f51d663fba6f/.cargo/config#L18 <https://github.com/rust-embedded/cortex-m-quickstart/blob/3cbcb9956acd638c0fb864937770f51d663fba6f/.cargo/config#L18> — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#298 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAFJU3JHI4PBXHBPLIUVYSLSKWTSZANCNFSM4SQFX3BA>.

[Adam Greig]

__sheap is defined in the linker script here; if you're not getting it it probably means the linker script is not being included. Regardless of gcc or lld linker, you need to pass -Tlink.x somehow or other, which is what that line in .cargo/config does. If you have a RUSTFLAGS environment variable set, it will override .cargo/config, or perhaps you're specifying another linker script somehow?

[Christopher Hunt]

Thanks. I’m getting the hang of this now. My situation is that I’ve got another nRF52 SDK C based project actually linking this Rust-based library statically. The nRF project is responsible for doing the linking and has a linker script already. So what’s the approach here… do I need to include just that one symbol from link.x, or am I looking to somehow merge link.x with my existing linker script?

…

On 15 Oct 2020, at 10:27 am, Adam Greig ***@***.***> wrote: __sheap is defined in the linker script here <https://github.com/rust-embedded/cortex-m-rt/blob/master/link.x.in#L162>; if you're not getting it it probably means the linker script is not being included. Regardless of gcc or lld linker, you need to pass -Tlink.x somehow or other, which is what that line in .cargo/config does. If you have a RUSTFLAGS environment variable set, it will override .cargo/config, or perhaps you're specifying another linker script somehow? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#298 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAFJU3JH6OMWK7EVZHF6DI3SKYXWXANCNFSM4SQFX3BA>.

[Christopher Hunt]

It occurs to me that I might not even need the cortex-m-rt library given that I’m calling Rust as a static lib and my nRF52 project has effectively set up its runtime. Obviously, I’ll need to take care of setting up an allocator etc… or am I in for a world of pain assuming an approach without cortex-m-rt?

…

On 15 Oct 2020, at 10:46 am, Christopher Hunt ***@***.***> wrote: Thanks. I’m getting the hang of this now. My situation is that I’ve got another nRF52 SDK C based project actually linking this Rust-based library statically. The nRF project is responsible for doing the linking and has a linker script already. So what’s the approach here… do I need to include just that one symbol from link.x, or am I looking to somehow merge link.x with my existing linker script? > On 15 Oct 2020, at 10:27 am, Adam Greig ***@***.*** ***@***.***>> wrote: > > > __sheap is defined in the linker script here <https://github.com/rust-embedded/cortex-m-rt/blob/master/link.x.in#L162>; if you're not getting it it probably means the linker script is not being included. Regardless of gcc or lld linker, you need to pass -Tlink.x somehow or other, which is what that line in .cargo/config does. If you have a RUSTFLAGS environment variable set, it will override .cargo/config, or perhaps you're specifying another linker script somehow? > > — > You are receiving this because you authored the thread. > Reply to this email directly, view it on GitHub <#298 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAFJU3JH6OMWK7EVZHF6DI3SKYXWXANCNFSM4SQFX3BA>. >

[Hanno Braun]

I have little experience with such C/Rust integrations, but I'd assume you're in a world of pain if you try to use cortex-m-rt and have some C-based runtime. cortex-m-rt will set up the vector table, do all the setup needed before entering main (copying/zeroing memory), etc. Which is all stuff that your C runtime presumable already does.

It's required for Rust applications. For a Rust library you only need the cortex-m crate, which will provide you some APIs, but won't interfere with another program that calls into your Rust code.

[Sympatron GmbH]

But I suppose @huntc would still have to define a global allocator if the Rust library depends on it. Is there some allocator one could use that uses malloc and free provided by the C runtime? Otherwise you would have to define 2 separate heaps, which is probably not desirable.

[Christopher Hunt]

Thanks for the replies, everyone. I'll keep this issue open as I'd like to ultimately raise a PR to improve the doc around calling static libs in an embedded context.

Meanwhile, I did provide my own allocator and things appear to work (although I'm having difficulty getting tests to work). Here's the gist of it - happy for feedback on the gist as I'm a Rust newbie:

https://gist.github.com/huntc/ab9a505683647aac7bccd2df0fc75f9e)

Thanks!

[Adam Greig]

I'm closing this issue while doing some backlog triage; please feel free to re-open if you do get back to documenting calling static libs in an embedded context, that would definitely be useful! Perhaps it could go into the Rust with C chapter of the book?