[PATCH v3] rust: Enable dynamic linking with llvm

[sunilkumar.dora@windriver.com]

From: Sunil Dora <sunilkumar.dora@windriver.com>

Fixes [Yocto #16058]

A segmentation fault occurs in rustc (e.g. in
llvm::X86ReadAdvanceTable) when reusing sstate artifacts built with
different host toolchain versions.

Issue sequence:
1. llvm-native is built with a newer toolchain
   (e.g. GCC 15/Binutils 2.45).
2. rust-native is later built with an older linker.
   (e.g. GCC 12/Binutils 2.40).
3. The older linker statically links parts of llvm-native into
   librustc_driver.
4. The resulting binary crashes at runtime inside the statically
   linked LLVM code.

The corruption happens at link time when mixing static native objects
produced by different toolchain generations.

Enable dynamic LLVM linking (link-shared = true) for rust-native so rustc
links against libLLVM.so instead of static archives, avoiding host linker
incompatibilities when reusing sstate artifacts.

Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
Suggested-by: Alexander Kanavin <alex@linutronix.de>
---
# v2 Feedback:
#   rust-native should link LLVM dynamically
#   rust-target should remain static
#   Workaround limited to -native only

 meta/recipes-devtools/rust/rust_1.93.0.bb | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/meta/recipes-devtools/rust/rust_1.93.0.bb b/meta/recipes-devtools/rust/rust_1.93.0.bb
index a25f65f674..2be0bd8d89 100644
--- a/meta/recipes-devtools/rust/rust_1.93.0.bb
+++ b/meta/recipes-devtools/rust/rust_1.93.0.bb
@@ -124,6 +124,8 @@ python do_configure() {
 
     # [llvm]
     config.add_section("llvm")
+    if d.getVar('PN') == "rust-native":
+        config.set("llvm", "link-shared", e(True))
     config.set("llvm", "static-libstdcpp", e(False))
     config.set("llvm", "download-ci-llvm", e(False))
     if "llvm" in (d.getVar('TC_CXX_RUNTIME') or ""):
-- 
2.49.0