[PATCH] rust: fix arm64 link failures when building rust apps

["S. Lockwood-Childs" <sjl@vctlabs.com>]

Typical error when trying to build a rust app (for example, librsvg)
for aarch64 targets looks like:
  undefined references to `__aarch64_ldadd8_rel'

The upstream rust commit
"add target feature outline-atomics" 0f9f241aac21bc77fb9e757da18207abefdc841d
has caused a number of such link failure regressions on platforms with aarch64
toolchains that are not able to cope with -moutline-atomics flag. This includes
musl toolchains [1] but some glibc toolchains also are not able to handle this
flag [2,3]

OE gcc-cross-aarch64 is currently one of the latter, but when it *is* able to
handle outline-atomics this patch should go away, to take advantage of the
reported performance benefit.

[1] https://github.com/rust-lang/git2-rs/issues/706
[2] https://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg661738.html
[3] https://bugzilla.redhat.com/show_bug.cgi?id=1830472

Signed-off-by: S. Lockwood-Childs <sjl@vctlabs.com>
---
 meta/recipes-devtools/rust/rust-target.inc    |  2 +
 .../rust/rust-disable-outline-atomics.patch   | 50 +++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 meta/recipes-devtools/rust/rust/rust-disable-outline-atomics.patch

diff --git a/meta/recipes-devtools/rust/rust-target.inc b/meta/recipes-devtools/rust/rust-target.inc
index 3f637b3ba5..bac743f66d 100644
--- a/meta/recipes-devtools/rust/rust-target.inc
+++ b/meta/recipes-devtools/rust/rust-target.inc
@@ -2,6 +2,8 @@ require rust.inc
 
 DEPENDS += "rust-llvm (=${PV})"
 
+SRC_URI += "file://rust-disable-outline-atomics.patch"
+
 # Otherwise we'll depend on what we provide
 INHIBIT_DEFAULT_RUST_DEPS:class-native = "1"
 # We don't need to depend on gcc-native because yocto assumes it exists
diff --git a/meta/recipes-devtools/rust/rust/rust-disable-outline-atomics.patch b/meta/recipes-devtools/rust/rust/rust-disable-outline-atomics.patch
new file mode 100644
index 0000000000..fc99a06a6a
--- /dev/null
+++ b/meta/recipes-devtools/rust/rust/rust-disable-outline-atomics.patch
@@ -0,0 +1,50 @@
+rust: fix arm64 link failures when building rust apps
+
+Typical error when trying to build a rust app looks like: 
+  undefined references to `__aarch64_ldadd8_rel'
+
+The upstream rust commit 
+"add target feature outline-atomics" 0f9f241aac21bc77fb9e757da18207abefdc841d
+has caused a number of such link failure regressions on platforms with aarch64
+toolchains that are not able to cope with -moutline-atomics flag. This includes
+musl toolchains [1] but some glibc toolchains also are not able to handle this
+flag [2,3]
+
+OE gcc-cross-aarch64 is currently one of the latter, but when it *is* able to
+handle outline-atomics this patch should go away, to take advantage of the
+reported performance benefit.
+
+[1] https://github.com/rust-lang/git2-rs/issues/706
+[2] https://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg661738.html
+[3] https://bugzilla.redhat.com/show_bug.cgi?id=1830472
+
+Upstream-Status: Inappropriate [other]
+
+Signed-off-by: S. Lockwood-Childs <sjl@vctlabs.com>
+
+diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
+index c2136f161..ca221eb4a 100644
+--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
++++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
+@@ -416,13 +416,14 @@ pub fn llvm_global_features(sess: &Session) -> Vec<String> {
+     // -Ctarget-features
+     features.extend(sess.opts.cg.target_feature.split(',').flat_map(&filter));
+ 
+-    // FIXME: Move outline-atomics to target definition when earliest supported LLVM is 12.
+-    if get_version() >= (12, 0, 0)
+-        && sess.target.llvm_target.contains("aarch64-unknown-linux")
+-        && sess.target.llvm_target != "aarch64-unknown-linux-musl"
+-    {
+-        features.push("+outline-atomics".to_string());
+-    }
++//    // FIXME: Move outline-atomics to target definition when earliest supported LLVM is 12.
++//    if get_version() >= (12, 0, 0)
++//        && sess.target.llvm_target.contains("aarch64-unknown-linux")
++//        && sess.target.llvm_target != "aarch64-unknown-linux-musl"
++//    {
++//        features.push("+outline-atomics".to_string());
++//    }
++
+ 
+     features
+ }
-- 
2.20.1