Add custom target for compiling relibc-freestanding for riscv64gc

mk/prefix.mk

@@ -234,6 +234,7 @@ else
 	export PATH="$(PREFIX_FREESTANDING_PATH):$$PATH" && \
 	export CARGO="env -u CARGO -u RUSTUP_TOOLCHAIN cargo" && \
 	export CC_$(subst -,_,$(TARGET))="$(GNU_TARGET)-gcc -isystem $(ROOT)/$@.partial/$(GNU_TARGET)/include" && \
+	export RUST_TARGET_PATH="$(ROOT)/targets" && \
 	$(MAKE) clean && \
 	$(MAKE) -j 1 all && \
 	$(MAKE) -j 1 install DESTDIR="$(ROOT)/$@.partial/$(GNU_TARGET)"

targets/README

@@ -0,0 +1,3 @@
+This contains a target definition for targets that Redox supports but have not
+yet been added to the upstream rust, specifically for compiling relibc in
+freestanding mode.

targets/riscv64gc-unknown-redox.json

@@ -0,0 +1,41 @@
+{
+  "arch": "riscv64",
+  "code-model": "medium",
+  "cpu": "generic-rv64",
+  "crt-objects-fallback": "false",
+  "crt-static-allows-dylibs": true,
+  "crt-static-default": true,
+  "crt-static-respected": true,
+  "data-layout": "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128",
+  "dynamic-linking": true,
+  "env": "relibc",
+  "features": "+m,+a,+f,+d,+c",
+  "has-rpath": true,
+  "has-thread-local": true,
+  "late-link-args": {
+    "gnu-cc": [
+      "-lgcc"
+    ],
+    "gnu-lld-cc": [
+      "-lgcc"
+    ]
+  },
+  "linker-flavor": "gnu-cc",
+  "llvm-abiname": "lp64d",
+  "llvm-target": "riscv64-unknown-redox",
+  "max-atomic-width": 64,
+  "metadata": {
+    "description": null,
+    "host_tools": null,
+    "std": null,
+    "tier": null
+  },
+  "os": "redox",
+  "plt-by-default": false,
+  "position-independent-executables": true,
+  "relro-level": "full",
+  "target-family": [
+    "unix"
+  ],
+  "target-pointer-width": "64"
+}