cmd/dist, cmd/link: allow passing default dynamic linker/loader

Add an environment variable to make.bash to allow setting the default
dynamic linker/loader. This fixes alpine builds to use
/lib/ld-musl-x86_64.so.1:

  $ readelf -l ../bin/go | grep 'interpreter:' | sed -e 's/^.*interpreter: \(.*\)[]]/\1/'
  /lib/ld-musl-x86_64.so.1

Also re-enable the internal linker tests that were previously disabled
for alpine (CL 41759, CL 41678).

Fixes #18243
Updates #19938

This resurrects CL 50070 authored by Jessie Frazelle.

Change-Id: I132b5282045a3d60c8568e3b002a7f075eac2d93
Reviewed-on: https://go-review.googlesource.com/c/163977
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/make.bash b/src/make.bash
index 13497eb039..b0e33cf6a4 100755
--- a/src/make.bash
+++ b/src/make.bash
@@ -34,6 +34,9 @@
 # controls the default behavior of the linker's -linkmode option.  The
 # default value depends on the system.
 #
+# GO_LDSO: Sets the default dynamic linker/loader (ld.so) to be used
+# by the internal linker.
+#
 # CC: Command line to run to compile C code for GOHOSTARCH.
 # Default is "gcc". Also supported: "clang".
 #
@@ -126,6 +129,15 @@ if [ "$(uname -s)" = "GNU/kFreeBSD" ]; then
 	export CGO_ENABLED=0
 fi
 
+# On Alpine Linux, use the musl dynamic linker/loader
+if [ -f "/etc/alpine-release" ]; then
+	if type readelf >/dev/null 2>&1; then
+		echo "int main() { return 0; }" | ${CC:-gcc} -o ./test-alpine-ldso -x c -
+		export GO_LDSO=$(readelf -l ./test-alpine-ldso | grep 'interpreter:' | sed -e 's/^.*interpreter: \(.*\)[]]/\1/')
+		rm -f ./test-alpine-ldso
+	fi
+fi
+
 # Clean old generated file that will cause problems in the build.
 rm -f ./runtime/runtime_defs.go