Support building rust modules against musl libc

Add a rust toolchain for musl libc, use std library built from source,
and add default dependencies on musl libc.

Bug: 216192129
Test: m USE_HOST_MUSL=true host-native
Change-Id: Ic5ff4487db9693aeb08a13405f4d18465eecdc4b

rust/config/x86_linux_host.go

@@ -22,12 +22,29 @@ import (
 
 var (
 	LinuxRustFlags     = []string{}
+	LinuxMuslRustFlags = []string{
+		// disable rustc's builtin fallbacks for crt objects
+		"-C link_self_contained=no",
+		// force rustc to use a dynamic musl libc
+		"-C target-feature=-crt-static",
+		"-Z link-native-libraries=no",
+	}
 	LinuxRustLinkFlags = []string{
 		"-B${cc_config.ClangBin}",
 		"-fuse-ld=lld",
 		"-Wl,--undefined-version",
+	}
+	LinuxRustGlibcLinkFlags = []string{
 		"--sysroot ${cc_config.LinuxGccRoot}/sysroot",
 	}
+	LinuxRustMuslLinkFlags = []string{
+		"--sysroot /dev/null",
+		"-nodefaultlibs",
+		"-nostdlib",
+		"-Wl,--no-dynamic-linker",
+		// for unwind
+		"-lgcc", "-lgcc_eh",
+	}
 	linuxX86Rustflags   = []string{}
 	linuxX86Linkflags   = []string{}
 	linuxX8664Rustflags = []string{}
@@ -35,15 +52,17 @@ var (
 )
 
 func init() {
-	registerToolchainFactory(android.Linux, android.X86_64, linuxX8664ToolchainFactory)
-	registerToolchainFactory(android.Linux, android.X86, linuxX86ToolchainFactory)
+	registerToolchainFactory(android.Linux, android.X86_64, linuxGlibcX8664ToolchainFactory)
+	registerToolchainFactory(android.Linux, android.X86, linuxGlibcX86ToolchainFactory)
 
-	// TODO: musl rust support
-	registerToolchainFactory(android.LinuxMusl, android.X86_64, linuxX8664ToolchainFactory)
-	registerToolchainFactory(android.LinuxMusl, android.X86, linuxX86ToolchainFactory)
+	registerToolchainFactory(android.LinuxMusl, android.X86_64, linuxMuslX8664ToolchainFactory)
+	registerToolchainFactory(android.LinuxMusl, android.X86, linuxMuslX86ToolchainFactory)
 
 	pctx.StaticVariable("LinuxToolchainRustFlags", strings.Join(LinuxRustFlags, " "))
+	pctx.StaticVariable("LinuxMuslToolchainRustFlags", strings.Join(LinuxMuslRustFlags, " "))
 	pctx.StaticVariable("LinuxToolchainLinkFlags", strings.Join(LinuxRustLinkFlags, " "))
+	pctx.StaticVariable("LinuxGlibcToolchainLinkFlags", strings.Join(LinuxRustGlibcLinkFlags, " "))
+	pctx.StaticVariable("LinuxMuslToolchainLinkFlags", strings.Join(LinuxRustMuslLinkFlags, " "))
 	pctx.StaticVariable("LinuxToolchainX86RustFlags", strings.Join(linuxX86Rustflags, " "))
 	pctx.StaticVariable("LinuxToolchainX86LinkFlags", strings.Join(linuxX86Linkflags, " "))
 	pctx.StaticVariable("LinuxToolchainX8664RustFlags", strings.Join(linuxX8664Rustflags, " "))
@@ -51,19 +70,9 @@ func init() {
 
 }
 
-type toolchainLinux struct {
-	toolchainRustFlags string
-	toolchainLinkFlags string
-}
-
-type toolchainLinuxX86 struct {
-	toolchain32Bit
-	toolchainLinux
-}
-
+// Base 64-bit linux rust toolchain
 type toolchainLinuxX8664 struct {
 	toolchain64Bit
-	toolchainLinux
 }
 
 func (toolchainLinuxX8664) Supported() bool {
@@ -78,10 +87,6 @@ func (t *toolchainLinuxX8664) Name() string {
 	return "x86_64"
 }
 
-func (t *toolchainLinuxX8664) RustTriple() string {
-	return "x86_64-unknown-linux-gnu"
-}
-
 func (t *toolchainLinuxX8664) ToolchainLinkFlags() string {
 	// Prepend the lld flags from cc_config so we stay in sync with cc
 	return "${cc_config.LinuxLldflags} ${cc_config.LinuxX8664Lldflags} " +
@@ -92,8 +97,49 @@ func (t *toolchainLinuxX8664) ToolchainRustFlags() string {
 	return "${config.LinuxToolchainRustFlags} ${config.LinuxToolchainX8664RustFlags}"
 }
 
-func linuxX8664ToolchainFactory(arch android.Arch) Toolchain {
-	return toolchainLinuxX8664Singleton
+// Specialization of the 64-bit linux rust toolchain for glibc.  Adds the gnu rust triple and
+// sysroot linker flags.
+type toolchainLinuxGlibcX8664 struct {
+	toolchainLinuxX8664
+}
+
+func (t *toolchainLinuxX8664) RustTriple() string {
+	return "x86_64-unknown-linux-gnu"
+}
+
+func (t *toolchainLinuxGlibcX8664) ToolchainLinkFlags() string {
+	return t.toolchainLinuxX8664.ToolchainLinkFlags() + " " + "${config.LinuxGlibcToolchainLinkFlags}"
+}
+
+func linuxGlibcX8664ToolchainFactory(arch android.Arch) Toolchain {
+	return toolchainLinuxGlibcX8664Singleton
+}
+
+// Specialization of the 64-bit linux rust toolchain for musl.  Adds the musl rust triple and
+// linker flags to avoid using the host sysroot.
+type toolchainLinuxMuslX8664 struct {
+	toolchainLinuxX8664
+}
+
+func (t *toolchainLinuxMuslX8664) RustTriple() string {
+	return "x86_64-unknown-linux-musl"
+}
+
+func (t *toolchainLinuxMuslX8664) ToolchainLinkFlags() string {
+	return t.toolchainLinuxX8664.ToolchainLinkFlags() + " " + "${config.LinuxMuslToolchainLinkFlags}"
+}
+
+func (t *toolchainLinuxMuslX8664) ToolchainRustFlags() string {
+	return t.toolchainLinuxX8664.ToolchainRustFlags() + " " + "${config.LinuxMuslToolchainRustFlags}"
+}
+
+func linuxMuslX8664ToolchainFactory(arch android.Arch) Toolchain {
+	return toolchainLinuxMuslX8664Singleton
+}
+
+// Base 32-bit linux rust toolchain
+type toolchainLinuxX86 struct {
+	toolchain32Bit
 }
 
 func (toolchainLinuxX86) Supported() bool {
@@ -116,10 +162,6 @@ func (toolchainLinuxX8664) LibclangRuntimeLibraryArch() string {
 	return "x86_64"
 }
 
-func (t *toolchainLinuxX86) RustTriple() string {
-	return "i686-unknown-linux-gnu"
-}
-
 func (t *toolchainLinuxX86) ToolchainLinkFlags() string {
 	// Prepend the lld flags from cc_config so we stay in sync with cc
 	return "${cc_config.LinuxLldflags} ${cc_config.LinuxX86Lldflags} " +
@@ -130,9 +172,47 @@ func (t *toolchainLinuxX86) ToolchainRustFlags() string {
 	return "${config.LinuxToolchainRustFlags} ${config.LinuxToolchainX86RustFlags}"
 }
 
-func linuxX86ToolchainFactory(arch android.Arch) Toolchain {
-	return toolchainLinuxX86Singleton
+// Specialization of the 32-bit linux rust toolchain for glibc.  Adds the gnu rust triple and
+// sysroot linker flags.
+type toolchainLinuxGlibcX86 struct {
+	toolchainLinuxX86
 }
 
-var toolchainLinuxX8664Singleton Toolchain = &toolchainLinuxX8664{}
-var toolchainLinuxX86Singleton Toolchain = &toolchainLinuxX86{}
+func (t *toolchainLinuxGlibcX86) RustTriple() string {
+	return "i686-unknown-linux-gnu"
+}
+
+func (t *toolchainLinuxGlibcX86) ToolchainLinkFlags() string {
+	return t.toolchainLinuxX86.ToolchainLinkFlags() + " " + "${config.LinuxGlibcToolchainLinkFlags}"
+}
+
+func linuxGlibcX86ToolchainFactory(arch android.Arch) Toolchain {
+	return toolchainLinuxGlibcX86Singleton
+}
+
+// Specialization of the 32-bit linux rust toolchain for musl.  Adds the musl rust triple and
+// linker flags to avoid using the host sysroot.
+type toolchainLinuxMuslX86 struct {
+	toolchainLinuxX86
+}
+
+func (t *toolchainLinuxMuslX86) RustTriple() string {
+	return "i686-unknown-linux-musl"
+}
+
+func (t *toolchainLinuxMuslX86) ToolchainLinkFlags() string {
+	return t.toolchainLinuxX86.ToolchainLinkFlags() + " " + "${config.LinuxMuslToolchainLinkFlags}"
+}
+
+func (t *toolchainLinuxMuslX86) ToolchainRustFlags() string {
+	return t.toolchainLinuxX86.ToolchainRustFlags() + " " + "${config.LinuxMuslToolchainRustFlags}"
+}
+
+func linuxMuslX86ToolchainFactory(arch android.Arch) Toolchain {
+	return toolchainLinuxMuslX86Singleton
+}
+
+var toolchainLinuxGlibcX8664Singleton Toolchain = &toolchainLinuxGlibcX8664{}
+var toolchainLinuxGlibcX86Singleton Toolchain = &toolchainLinuxGlibcX86{}
+var toolchainLinuxMuslX8664Singleton Toolchain = &toolchainLinuxMuslX8664{}
+var toolchainLinuxMuslX86Singleton Toolchain = &toolchainLinuxMuslX86{}