tools/mpy_ld.py: Add RV64 natmod support.

This commit adds the ability to compile native modules for the RV64
platform, using "rv64imc" as its architecture name (eg.
"make ARCH=rv64imc" should build a RV64 natmod).

The rest of 64-bits relocations needed to build a native module are now
implemented, and all sample native modules build without errors or
warnings.  The same Picolibc caveats on RV32 also apply on RV64, thus
the documentation was updated accordingly.

RV64 native modules are also built as part of the CI process, but not
yet executed as the QEMU port is not yet able to load and run them.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>

tools/mpy_ld.py

@@ -49,6 +49,7 @@ MP_NATIVE_ARCH_ARMV7EMDP = 8
 MP_NATIVE_ARCH_XTENSA = 9
 MP_NATIVE_ARCH_XTENSAWIN = 10
 MP_NATIVE_ARCH_RV32IMC = 11
+MP_NATIVE_ARCH_RV64IMC = 12
 MP_PERSISTENT_OBJ_STR = 5
 MP_SCOPE_FLAG_VIPERRELOC = 0x10
 MP_SCOPE_FLAG_VIPERRODATA = 0x20
@@ -62,6 +63,7 @@ R_RISCV_32 = 1
 R_X86_64_64 = 1
 R_XTENSA_32 = 1
 R_386_PC32 = 2
+R_RISCV_64 = 2
 R_X86_64_PC32 = 2
 R_ARM_ABS32 = 2
 R_386_GOT32 = 3
@@ -175,7 +177,7 @@ def asm_jump_xtensa(entry):
     return struct.pack("<BH", jump_op & 0xFF, jump_op >> 8)
 
 
-def asm_jump_rv32(entry):
+def asm_jump_riscv(entry):
     # This could be 6 bytes shorter, but the code currently cannot
     # support a trampoline with varying length depending on the offset.
 
@@ -261,7 +263,14 @@ ARCH_DATA = {
         MP_NATIVE_ARCH_RV32IMC << 2,
         4,
         (R_RISCV_32, R_RISCV_GOT_HI20, R_RISCV_GOT32_PCREL),
-        asm_jump_rv32,
+        asm_jump_riscv,
+    ),
+    "rv64imc": ArchData(
+        "EM_RISCV",
+        MP_NATIVE_ARCH_RV64IMC << 2,
+        8,
+        (R_RISCV_64, R_RISCV_GOT_HI20, R_RISCV_GOT32_PCREL),
+        asm_jump_riscv,
     ),
 }
 
@@ -779,7 +788,7 @@ def do_relocation_data(env, text_addr, r):
         or env.arch.name == "EM_XTENSA"
         and r_info_type == R_XTENSA_32
         or env.arch.name == "EM_RISCV"
-        and r_info_type == R_RISCV_32
+        and r_info_type in (R_RISCV_32, R_RISCV_64)
     ):
         # Relocation in data.rel.ro to internal/external symbol
         if env.arch.word_size == 4: