package/libunwind: add libucontext support

We can expand the list of supported musl architectures by
letting libucontext provide required context API's.

Use the following table to determine which architectures require
libucontext for BR2_PACKAGE_LIBUNWIND_MUSL_CONTEXT_REQUIRED:
https://github.com/libunwind/libunwind/tree/v1.6.2#libc-requirements

Enable BR2_PACKAGE_LIBUNWIND_ARCH_SUPPORTS if we have
BR2_PACKAGE_LIBUCONTEXT_ARCH_SUPPORTS or if context is not required
by checking for !BR2_PACKAGE_LIBUNWIND_MUSL_CONTEXT_REQUIRED.

Select BR2_PACKAGE_LIBUCONTEXT when selecting BR2_PACKAGE_LIBUNWIND
if we have BR2_PACKAGE_LIBUNWIND_MUSL_CONTEXT_REQUIRED.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>

package/libunwind/Config.in

@@ -1,3 +1,17 @@
+config BR2_PACKAGE_LIBUNWIND_MUSL_CONTEXT_REQUIRED
+	bool
+	default y
+	depends on !BR2_ARM_CPU_HAS_ARM
+	depends on !BR2_aarch64
+	depends on !BR2_aarch64_be
+	depends on !BR2_mips
+	depends on !BR2_mipsel
+	depends on !BR2_mips64
+	depends on !BR2_mips64el
+	depends on !BR2_riscv
+	depends on !BR2_x86_64
+	depends on BR2_TOOLCHAIN_USES_MUSL
+
 # libunwind is only available for a certain subset of the
 # architectures (as visible in the list of architectures supported
 # with the glibc C library below).
@@ -17,7 +31,8 @@ config BR2_PACKAGE_LIBUNWIND_ARCH_SUPPORTS
 		(BR2_ARM_CPU_HAS_ARM || BR2_mips || BR2_mipsel || \
 		 BR2_mips64 || BR2_mips64el || BR2_x86_64)
 	default y if BR2_TOOLCHAIN_USES_MUSL && \
-		(BR2_ARM_CPU_HAS_ARM || BR2_aarch64 || BR2_x86_64)
+		(!BR2_PACKAGE_LIBUNWIND_MUSL_CONTEXT_REQUIRED || \
+		 BR2_PACKAGE_LIBUCONTEXT_ARCH_SUPPORTS)
 
 config BR2_PACKAGE_LIBUNWIND
 	bool "libunwind"
@@ -27,6 +42,8 @@ config BR2_PACKAGE_LIBUNWIND
 	# forcefully links against libgcc_s, only available in dynamic
 	# linking configurations
 	depends on !BR2_STATIC_LIBS
+	select BR2_PACKAGE_LIBUCONTEXT if BR2_TOOLCHAIN_USES_MUSL && \
+		BR2_PACKAGE_LIBUNWIND_MUSL_CONTEXT_REQUIRED
 	help
 	  C API to determine the call-chain of a program.
 

package/libunwind/libunwind.mk

@@ -16,4 +16,8 @@ LIBUNWIND_CONF_OPTS = \
 	--disable-tests \
 	$(if $(BR2_INSTALL_LIBSTDCPP),--enable-cxx-exceptions,--disable-cxx-exceptions)
 
+ifeq ($(BR2_PACKAGE_LIBUCONTEXT),y)
+LIBUNWIND_DEPENDENCIES += libucontext
+endif
+
 $(eval $(autotools-package))