LoongArch: Enable initial Rust support

Enable initial Rust support for LoongArch.

Tested-by: Miguel Ojeda <[e-mail]>
Signed-off-by: WANG Rui <[e-mail]>
Signed-off-by: Huacai Chen <[e-mail]>

Documentation/rust/arch-support.rst

···
 Below is a general summary of architectures that currently work. Level of
 support corresponds to ``S`` values in the ``MAINTAINERS`` file.
 
-============  ================  ==============================================
-Architecture  Level of support  Constraints
-============  ================  ==============================================
-``um``        Maintained        ``x86_64`` only.
-``x86``       Maintained        ``x86_64`` only.
-============  ================  ==============================================
+=============  ================  ==============================================
+Architecture   Level of support  Constraints
+=============  ================  ==============================================
+``loongarch``  Maintained        -
+``um``         Maintained        ``x86_64`` only.
+``x86``        Maintained        ``x86_64`` only.
+=============  ================  ==============================================
 

arch/loongarch/Kconfig

···
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RETHOOK
 	select HAVE_RSEQ
+	select HAVE_RUST
 	select HAVE_SAMPLE_FTRACE_DIRECT
 	select HAVE_SAMPLE_FTRACE_DIRECT_MULTI
 	select HAVE_SETUP_PER_CPU_AREA if NUMA

arch/loongarch/Makefile

···
 KBUILD_CFLAGS_MODULE		+= -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs
 endif
 
+KBUILD_RUSTFLAGS_MODULE		+= -Crelocation-model=pic
+
 ifeq ($(CONFIG_RELOCATABLE),y)
 KBUILD_CFLAGS_KERNEL		+= -fPIE
+KBUILD_RUSTFLAGS_KERNEL		+= -Crelocation-model=pie
 LDFLAGS_vmlinux			+= -static -pie --no-dynamic-linker -z notext $(call ld-option, --apply-dynamic-relocs)
 endif
 

scripts/generate_rust_target.rs

···
         ts.push("features", features);
         ts.push("llvm-target", "x86_64-linux-gnu");
         ts.push("target-pointer-width", "64");
+    } else if cfg.has("LOONGARCH") {
+        ts.push("arch", "loongarch64");
+        ts.push("data-layout", "e-m:e-p:64:64-i64:64-i128:128-n64-S128");
+        ts.push("features", "-f,-d");
+        ts.push("llvm-target", "loongarch64-linux-gnusf");
+        ts.push("llvm-abiname", "lp64s");
+        ts.push("target-pointer-width", "64");
     } else {
         panic!("Unsupported architecture");
     }