cmd/go: add GORISCV64 environment variable

The variable represents the RISC-V user-mode application profile for
which to compile.  Valid values are rva20u64 (the default) and
rva22u64.

Setting GORISCV64=rva20u64 defines the riscv64.rva20u64 build tag,
sets the internal variable buildcfg.GORISCV64 to 20 and defines the
macro GORISCV64_rva20u64 for use in assembly language code.

Setting GORISCV64=rva22u64 defines the riscv64.rva20u64 and
riscv64.rva22u64 build tags, sets the internal variable
buildcfg.GORISCV64 to 22 and defines the macro GORISCV64_rva22u64
for use in assembly language code.

This patch only provides a mechanism for the compiler and hand-coded
assembly language functions to take advantage of the RISC-V
extensions mandated by the application profiles.  Further patches
will be required to get the compiler/assembler and assembly language
functions to actually generate and use these extensions.

Fixes #61476

Change-Id: I9195ae6ee71703cd2112160e89157ab63b8391af
Reviewed-on: https://go-review.googlesource.com/c/go/+/541135
Reviewed-by: M Zhuo <mengzhuo1203@gmail.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Wang Yaduo <wangyaduo@linux.alibaba.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: M Zhuo <mengzhuo1203@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

2 files changed, 16 insertions, 0 deletions

diff --git a/src/cmd/dist/build.go b/src/cmd/dist/build.go
index 32e59b446a..96199bcbfa 100644
--- a/src/cmd/dist/build.go
+++ b/src/cmd/dist/build.go
@@ -38,6 +38,7 @@ var (
 	gomips           string
 	gomips64         string
 	goppc64          string
+	goriscv64        string
 	goroot           string
 	goroot_final     string
 	goextlinkenabled string
@@ -177,6 +178,12 @@ func xinit() {
 	}
 	goppc64 = b
 
+	b = os.Getenv("GORISCV64")
+	if b == "" {
+		b = "rva20u64"
+	}
+	goriscv64 = b
+
 	if p := pathf("%s/src/all.bash", goroot); !isfile(p) {
 		fatalf("$GOROOT is not set correctly or not exported\n"+
 			"\tGOROOT=%s\n"+
@@ -236,6 +243,7 @@ func xinit() {
 	os.Setenv("GOMIPS", gomips)
 	os.Setenv("GOMIPS64", gomips64)
 	os.Setenv("GOPPC64", goppc64)
+	os.Setenv("GORISCV64", goriscv64)
 	os.Setenv("GOROOT", goroot)
 	os.Setenv("GOROOT_FINAL", goroot_final)
 
@@ -891,6 +899,10 @@ func runInstall(pkg string, ch chan struct{}) {
 			asmArgs = append(asmArgs, "-D", "GOPPC64_power8")
 		}
 	}
+	if goarch == "riscv64" {
+		// Define GORISCV64_value from goriscv64
+		asmArgs = append(asmArgs, "-D", "GORISCV64_"+goriscv64)
+	}
 	goasmh := pathf("%s/go_asm.h", workdir)
 
 	// Collect symabis from assembly code.
@@ -1236,6 +1248,9 @@ func cmdenv() {
 	if goarch == "ppc64" || goarch == "ppc64le" {
 		xprintf(format, "GOPPC64", goppc64)
 	}
+	if goarch == "riscv64" {
+		xprintf(format, "GORISCV64", goriscv64)
+	}
 	xprintf(format, "GOWORK", "off")
 
 	if *path {
diff --git a/src/cmd/dist/buildruntime.go b/src/cmd/dist/buildruntime.go
index 1de78f0fdb..b041183bdf 100644
--- a/src/cmd/dist/buildruntime.go
+++ b/src/cmd/dist/buildruntime.go
@@ -57,6 +57,7 @@ func mkbuildcfg(file string) {
 	fmt.Fprintf(&buf, "const defaultGOMIPS = `%s`\n", gomips)
 	fmt.Fprintf(&buf, "const defaultGOMIPS64 = `%s`\n", gomips64)
 	fmt.Fprintf(&buf, "const defaultGOPPC64 = `%s`\n", goppc64)
+	fmt.Fprintf(&buf, "const defaultGORISCV64 = `%s`\n", goriscv64)
 	fmt.Fprintf(&buf, "const defaultGOEXPERIMENT = `%s`\n", goexperiment)
 	fmt.Fprintf(&buf, "const defaultGO_EXTLINK_ENABLED = `%s`\n", goextlinkenabled)
 	fmt.Fprintf(&buf, "const defaultGO_LDSO = `%s`\n", defaultldso)