Re: [PATCH] rust: Enable dynamic linking with llvm

["Dora, Sunil Kumar" <SunilKumar.Dora@windriver.com>]

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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.

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