added support for more granular RISCV32/64 ISA extensions

Author: cordawyn

CMakeLists.txt

@@ -42,10 +42,47 @@ function(_rust_map_target)
   elseif(CONFIG_RISCV)
     if(CONFIG_RISCV_ISA_RV64I)
       # TODO: Should fail if the extensions don't match.
-      set(RUST_TARGET "riscv64imac-unknown-none-elf" PARENT_SCOPE)
+      # We have multiple choices, try to pick the best.
+      # Note that Rust currently only supports "riscv64gc" and "riscv64imac" targets!
+      set(RUST_TARGET "riscv64")
+      if(CONFIG_RISCV_ISA_EXT_G)
+        set(RUST_TARGET "${RUST_TARGET}g")
+      else()
+        set(RUST_TARGET "${RUST_TARGET}i")
+        if(CONFIG_RISCV_ISA_EXT_M)
+          set(RUST_TARGET "${RUST_TARGET}m")
+        endif()
+        if(CONFIG_RISCV_ISA_EXT_A)
+          set(RUST_TARGET "${RUST_TARGET}a")
+        endif()
+        if(CONFIG_RISCV_ISA_EXT_F)
+          set(RUST_TARGET "${RUST_TARGET}f")
+        endif()
+        if(CONFIG_RISCV_ISA_EXT_D)
+          set(RUST_TARGET "${RUST_TARGET}d")
+        endif()
+      endif()
+      if(CONFIG_RISCV_ISA_EXT_C)
+        set(RUST_TARGET "${RUST_TARGET}c")
+      endif()
+      set(RUST_TARGET "${RUST_TARGET}-unknown-none-elf" PARENT_SCOPE)
     elseif(CONFIG_RISCV_ISA_RV32I)
-      # TODO: We have multiple choices, try to pick the best.
-      set(RUST_TARGET "riscv32i-unknown-none-elf" PARENT_SCOPE)
+      # We have multiple choices, try to pick the best.
+      # Note that Rust currently only supports subsets of "riscv32imafc" targets!
+      set(RUST_TARGET "riscv32i")
+      if(CONFIG_RISCV_ISA_EXT_M)
+        set(RUST_TARGET "${RUST_TARGET}m")
+      endif()
+      if(CONFIG_RISCV_ISA_EXT_A)
+        set(RUST_TARGET "${RUST_TARGET}a")
+      endif()
+      if(CONFIG_RISCV_ISA_EXT_F)
+        set(RUST_TARGET "${RUST_TARGET}f")
+      endif()
+      if(CONFIG_RISCV_ISA_EXT_C)
+        set(RUST_TARGET "${RUST_TARGET}c")
+      endif()
+      set(RUST_TARGET "${RUST_TARGET}-unknown-none-elf" PARENT_SCOPE)
     else()
       message(FATAL_ERROR "Rust: Unsupported riscv ISA")
     endif()