Re: [OE-core] [PATCH] rust: Enable dynamic linking with llvm

[Randy MacLeod <randy.macleod@windriver.com>]

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On 2026-02-13 2:51 p.m., Dora, Sunil Kumar via lists.openembedded.org wrote:
> On Thu, Feb 12, 2026 at 10:36 PM, Ross Burton wrote:
>
>     What’s the impact on the native sysroot and target packages when
>     we link rust against all of libLLVM.so dynamically vs statically
>     linking the pieces that are used?
>
> Hi Ross,
>
> Below are the observed impacts when linking Rust against shared 
> libLLVM.so versus
> statically linking LLVM components.
>
> On Native:
> **********
> All required LLVM-related libraries were already present in 
> recipe-sysroot-native before switching
> Rust to dynamic LLVM. Dynamic linking does not introduce any new 
> native dependencies.
> Existing llvm-native artifacts are reused.
>
> Static:
> -rw-r--r-- 1 xxx users 213M Feb 13 00:29 
> librustc_driver-4b6f2c2478f9ef2c.so
> Dynamic:
> -rw-r--r-- 1 xxx users 132M Feb 13 00:52 
> librustc_driver-4b6f2c2478f9ef2c.so
>
> So on native we see ~81 MB reduction in librustc_driver, with no 
> additional sysroot growth.
>
> On Target:
> **********
> librustc_driver shrinks from 144.8 MB to 84.2 MB (~60 MB reduction).
> However, dynamic linking introduces shared libLLVM.so plus a few 
> runtime dependencies.
>
> Static:
> root@qemux86-64:~# ls -lh /usr/lib/librustc_driver-*.so
> -rw-r--r--    1 root     root      144.8M Apr  5  2011 
> /usr/lib/librustc_driver-151eed90355bbdac.so
>
> Dynamic:
> root@qemux86-64:~# ls -lh /usr/lib/librustc_driver-*.so
> -rw-r--r--    1 root     root       84.2M Apr  5  2011 
> /usr/lib/librustc_driver-151eed90355bbdac.so
>
> New dynamic dependencies:
> root@qemux86-64:~# ldd /usr/lib/librustc_driver-*.so
>         libLLVM.so.21.1 libffi.so.8 libxml2.so.16
>
> Size contribution on target:
>  - libLLVM.so.21.1 ≈ 75.5 MB
>  - libxml2.so.16 ≈ 1.2 MB
>  - libffi.so.8 ≈ 42.5 KB
>
> When LLVM is only used by Rust, this results in a net image increase 
> of approximately 15–16 MB.


Good, that's annoying but acceptable increase: ~7% to work-around this bug.

I'm still a bit uncomfortable with changing the way that target Rust is 
built to deal with
a Rust-native problem. Also there's the question about dynamic linking 
increasing runtime
by a small amount. Finally, I worry that few people/distros change the 
default linking to by dynamic.

So I won't object to this work-around especially if we can easily limit 
it to -native. Have you tried that?
In a few years, we won't have this mix of toolchain versions and can 
drop this change

so if this gets merged please open a tracking bug so that we don't forget.

../Randy



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-- 
# Randy MacLeod
# Wind River Linux

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