Prevent musl riscv32 builds

The upstream musl libc does not support 32bit RISC-V builds.
We therefore only allow building the 64bit version (i.e.,
riscv64-unknown-linux-musl-).

Signed-off-by: Florian Hofhammer <florian.hofhammer@fhofhammer.de>

Author: florianhofhammer

.github/workflows/build.yaml

@@ -16,6 +16,9 @@ jobs:
         os:     [ubuntu-18.04, ubuntu-20.04]
         mode:   [newlib, linux, musl]
         target: [rv32gc-ilp32d, rv64gc-lp64d]
+        exclude:
+          - mode: musl
+            target: rv32gc-ilp32d
     steps:
       - uses: actions/checkout@v2
 

.github/workflows/nightly-release.yaml

@@ -51,6 +51,9 @@ jobs:
         os:     [ubuntu-18.04, ubuntu-20.04]
         mode:   [newlib, linux, musl]
         target: [rv32gc-ilp32d, rv64gc-lp64d]
+        exclude:
+          - mode: musl
+            target: rv32gc-ilp32d
     steps:
       - uses: actions/checkout@v2
 

Makefile.in

@@ -102,7 +102,13 @@ CONFIGURE_HOST   = @configure_host@
 all: @default_target@
 newlib: stamps/build-gcc-newlib-stage2
 linux: stamps/build-gcc-linux-stage2
+ifneq (,$(findstring riscv32,$(MUSL_TUPLE)))
+.PHONY: musl
+musl:
+	@echo "musl only supports 64bit builds." && exit 1
+else
 musl: stamps/build-gcc-musl-stage2
+endif
 ifeq (@enable_gdb@,--enable-gdb)
 newlib: stamps/build-gdb-newlib
 linux: stamps/build-gdb-linux

README.md

@@ -94,11 +94,16 @@ To build either cross-compiler with support for both 32-bit and
 And then either `make`, `make linux` or `make musl` for the Newlib, Linux
 glibc-based or Linux musl libc-based cross-compiler, respectively.
 
-The multilib compiler will have the prefix riscv64-unknown-elf-,
-riscv64-unknown-linux-gnu- or riscv64-unknown-linux-musl-
-but will be able to target both 32-bit and 64-bit systems. It will support
-the most common `-march`/`-mabi` options, which can be seen by using the
-`--print-multi-lib` flag on either cross-compiler.
+The multilib compiler will have the prefix riscv64-unknown-elf- or
+riscv64-unknown-linux-gnu- but will be able to target both 32-bit and 64-bit
+systems.
+It will support the most common `-march`/`-mabi` options, which can be seen by
+using the `--print-multi-lib` flag on either cross-compiler.
+
+The musl compiler (riscv64-unknown-linux-musl-) will only be able to target
+64-bit systems due to limitations in the upstream musl architecture support.
+The `--enable-multilib` flag therefore does not actually enable multilib support
+for musl libc.
 
 ### Troubleshooting Build Problems
 

configure

@@ -1320,7 +1320,7 @@ Optional Features:
   --enable-FEATURE[=ARG]  include FEATURE [ARG=yes]
   --enable-linux          set linux as the default make target
                           [--disable-linux]
-  --enable-multilib       build both RV32 and RV64 runtime libraries
+  --enable-multilib       build both RV32 and RV64 runtime libraries (only RV64 for musl libc)
                           [--disable-multilib]
   --enable-gcc-checking   Enable gcc internal checking, it will make gcc very
                           slow, only enable it when developing gcc

configure.ac

@@ -89,7 +89,7 @@ AC_SUBST(WITH_TUNE, --with-tune=$with_tune)
 
 AC_ARG_ENABLE(multilib,
 	[AS_HELP_STRING([--enable-multilib],
-		[build both RV32 and RV64 runtime libraries @<:@--disable-multilib@:>@])],
+		[build both RV32 and RV64 runtime libraries (only RV64 for musl libc) @<:@--disable-multilib@:>@])],
 	[],
 	[enable_multilib=no]
 	)
@@ -118,6 +118,10 @@ AS_IF([test "x$enable_multilib" != xno],
         [AC_SUBST(newlib_multilib_names,"rv32i-ilp32 rv32iac-ilp32 rv32im-ilp32 rv32imac-ilp32 rv32imafc-ilp32f rv64imac-lp64 rv64imafdc-lp64d")],
         [AC_SUBST(newlib_multilib_names,"$with_arch-$with_abi")])
 
+AS_IF([test "x$enable_multilib" != xno],
+        [AC_SUBST(musl_multilib_names,"rv64imac-lp64 rv64imafdc-lp64d")],
+        [AC_SUBST(musl_multilib_names,"$with_arch-$with_abi")])
+
 AC_ARG_ENABLE(gcc-checking,
         [AS_HELP_STRING([--enable-gcc-checking],
 		[Enable gcc internal checking, it will make gcc very slow, only enable it when developing gcc @<:@--disable-gcc-checking@:>@])],