Add notes for cross-compilation to gcc-only targets

Readme.md

@@ -116,3 +116,20 @@ p loc->m_line
  * Build the stage1 compiler (`rustup toolchain link debug-current stage2 build/x86_64-unknown-linux-gnu/stage1`).
  * Clean and rebuild the codegen with `debug-current` in the file `rust-toolchain`.
  * Add `~/.rustup/toolchains/debug-current/lib/rustlib/x86_64-unknown-linux-gnu/lib` to `LD_LIBRARY_PATH`.
+
+### How to build a cross-compiling libgccjit
+
+#### Building libgccjit
+
+ * Follow these instructions: https://preshing.com/20141119/how-to-build-a-gcc-cross-compiler/ with the following changes:
+ * Configure gcc with `../gcc/configure --enable-host-shared --disable-multilib --enable-languages=c,jit,c++ --disable-bootstrap --enable-checking=release --prefix=/opt/m68k-gcc/ --target=m68k-linux --without-headers`.
+ * Some shells, like fish, don't define the environment variable `$MACHTYPE`.
+ * Add `CFLAGS="-Wno-error=attributes -g -O2"` at the end of the configure command for building glibc (`CFLAGS="-Wno-error=attributes -Wno-error=array-parameter -Wno-error=stringop-overflow -Wno-error=array-bounds -g -O2"` for glibc 2.31, which is useful for Debian).
+
+#### Configuring rustc_codegen_gcc
+
+ * Set `TARGET_TRIPLE="m68k-unknown-linux-gnu"` in config.sh.
+ * Since rustc doesn't support this architecture yet, set it back to `TARGET_TRIPLE="mips-unknown-linux-gnu"` (or another target having the same attributes).
+ * Set `linker='-Clinker=m68k-linux-gcc'`.
+ * Set the path to the cross-compiling libgccjit in `gcc_path`.
+ * Disable the 128-bit integer types if the target doesn't support them by using `let i128_type = context.new_type::<i64>();` in `context.rs` (same for u128_type).

config.sh

@@ -16,12 +16,15 @@ fi
 
 HOST_TRIPLE=$(rustc -vV | grep host | cut -d: -f2 | tr -d " ")
 TARGET_TRIPLE=$HOST_TRIPLE
-#TARGET_TRIPLE="aarch64-unknown-linux-gnu"
+#TARGET_TRIPLE="m68k-unknown-linux-gnu"
 
 linker=''
 RUN_WRAPPER=''
 if [[ "$HOST_TRIPLE" != "$TARGET_TRIPLE" ]]; then
-   if [[ "$TARGET_TRIPLE" == "aarch64-unknown-linux-gnu" ]]; then
+   if [[ "$TARGET_TRIPLE" == "m68k-unknown-linux-gnu" ]]; then
+       TARGET_TRIPLE="mips-unknown-linux-gnu"
+       linker='-Clinker=m68k-linux-gcc'
+   elif [[ "$TARGET_TRIPLE" == "aarch64-unknown-linux-gnu" ]]; then
       # We are cross-compiling for aarch64. Use the correct linker and run tests in qemu.
       linker='-Clinker=aarch64-linux-gnu-gcc'
       RUN_WRAPPER='qemu-aarch64 -L /usr/aarch64-linux-gnu'

src/base.rs

@@ -74,8 +74,12 @@ pub fn compile_codegen_unit<'tcx>(tcx: TyCtxt<'tcx>, cgu_name: Symbol) -> (Modul
         // Instantiate monomorphizations without filling out definitions yet...
         //let llvm_module = ModuleLlvm::new(tcx, &cgu_name.as_str());
         let context = Context::default();
-        // TODO(antoyo): only set on x86 platforms.
-        context.add_command_line_option("-masm=intel");
+
+        if tcx.sess.target.arch.starts_with("x86") {
+            // TODO(antoyo): check tcx.sess.asm_arch instead?
+            context.add_command_line_option("-masm=intel");
+        }
+
         for arg in &tcx.sess.opts.cg.llvm_args {
             context.add_command_line_option(arg);
         }