proposal: x/build: add a CI runner with CC="zig cc" for linux/amd64

[motiejus]

Short Summary

Add a CI worker that runs Go's unit tests with CC="zig cc" on linux/amd64.

About zig cc

On Linux, zig cc is a wrapper on top of LLVM and LLD. Main benefits compared to other popular compilers:

• Cross-compilation out of the box via a command-line flag.
• Can dynamically link to a specified glibc version via a command-line flag (i.e. it generates a libc.so.6 on the fly before linking, no need to ship one).

For example:

CC="zig cc -target aarch64-linux-gnu.2.17" go build .

Will (cross-)compile the current package for linux/arm64 and link to glibc 2.17. Read this to learn more about zig cc.

Zig also has it's own Mach-O linker, making it possible to cross-compile to OS X. This is not in scope for this proposal, but may be considered as a next step. cc @kubkon who expressed interest in this.

Logistics

Initial changes:

1. Add a linux/amd64 worker that lack any C/C++ compiler (i.e. make sure gcc/ld are not installed).
2. Install zig v0.11 (to be released in May) to the worker.
3. Run all Golang's unit tests with CC="zig cc".

Upkeep:

1. The CI worker will have ReleaseSafe+Debug build, so, in case Zig crashes or trips an assertion, there will be decent information about the crash right in the logs. Refs Proposal: change nightlies from ReleaseFast to ReleaseSafe+debug ziglang/zig#15194.
2. The worker should have Zig upgraded when a new Zig version is released. This can be coordinated by Uber's Go team (cc @linzhp @sywhang) or Zig folks (cc @kubkon @andrewrk).

Why is this important?

As of writing a few companies are known to use zig cc to compile C/C++ (via this toolchain) and bundle it with Go code. My employer Uber uses zig cc to compile+link it's Go Monorepo for linux/amd64 and linux/arm64. During the last 4 months that we have been using zig cc in production (which included an upgrade to Go 1.20) we have encountered some issues in a released Go version that would have been caught in dev versions should zig cc worker be present:

• runtime/pprof: missing profile info for CGo code when compiled with CC="zig cc" #59466
• cmd/link: Incorrect symbol linked in darwin/arm64 #58935 - any Go 1.20-1.20.2 executable on darwin/arm64 would have triggered an assertion during linking with Zig.

Since Go unit tests is a decent "integration" test, we believe it is a worth-while exercise to have this in CI.

[seankhliao]

cc @golang/release

[motiejus]

For the record, Go unit tests pass on linux/amd64 with the patch below.

How to run the unit tests (click here)

zig-cc

#!/bin/sh
export ZIG_GLOBAL_CACHE_DIR=/tmp/zig-global-cache
exec /usr/local/bin/zig cc -fno-sanitize=undefined "$@"

And this patch:

diff --git a/src/cmd/cgo/internal/testshared/shared_test.go b/src/cmd/cgo/internal/testshared/shared_test.go
index 34cf3f3141..5e5dbaea13 100644
--- a/src/cmd/cgo/internal/testshared/shared_test.go
+++ b/src/cmd/cgo/internal/testshared/shared_test.go
@@ -12,6 +12,7 @@ import (
        "flag"
        "fmt"
        "go/build"
+       "internal/testenv"
        "io"
        "log"
        "os"
@@ -682,6 +683,11 @@ func TestNotes(t *testing.T) {
 // runtime, another package (dep2) that links against the first, and an
 // executable that links against dep2.
 func TestTwoGopathShlibs(t *testing.T) {
+       // -buildmode=shared is to be removed (#47788). Does not work with linux zig-cc.
+       b := testenv.Builder()
+       if strings.HasPrefix(b, "linux-") && strings.HasSuffix(b, "-zig-cc") {
+               t.Skipf("skipping on linux zig-cc")
+       }
        goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
        goCmd(t, "install", "-buildmode=shared", "-linkshared", "./dep2")
        goCmd(t, "install", "-linkshared", "./exe2")
@@ -689,6 +695,11 @@ func TestTwoGopathShlibs(t *testing.T) {
 }
 
 func TestThreeGopathShlibs(t *testing.T) {
+       // -buildmode=shared is to be removed (#47788). Does not work with linux zig-cc.
+       b := testenv.Builder()
+       if strings.HasPrefix(b, "linux-") && strings.HasSuffix(b, "-zig-cc") {
+               t.Skipf("skipping on linux zig-cc")
+       }
        goCmd(t, "install", "-buildmode=shared", "-linkshared", "./depBase")
        goCmd(t, "install", "-buildmode=shared", "-linkshared", "./dep2")
        goCmd(t, "install", "-buildmode=shared", "-linkshared", "./dep3")
@@ -1085,6 +1096,11 @@ func TestPackageOrder(t *testing.T) {
 // Test that GC data are generated correctly by the linker when it needs a type defined in
 // a shared library. See issue 39927.
 func TestGCData(t *testing.T) {
+       // -buildmode=shared is to be removed (#47788). Does not work with linux zig-cc.
+       b := testenv.Builder()
+       if strings.HasPrefix(b, "linux-") && strings.HasSuffix(b, "-zig-cc") {
+               t.Skipf("skipping on linux zig-cc")
+       }
        goCmd(t, "install", "-buildmode=shared", "-linkshared", "./gcdata/p")
        goCmd(t, "build", "-linkshared", "./gcdata/main")
        runWithEnv(t, "running gcdata/main", []string{"GODEBUG=clobberfree=1"}, "./main")
diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go
index 04dfd22f88..1aebf7bded 100644
--- a/src/cmd/dist/test.go
+++ b/src/cmd/dist/test.go
@@ -1113,6 +1113,14 @@ func (t *tester) internalLink() bool {
                // linkmode=internal isn't supported.
                return false
        }
+
+       // internal linkmode does not always work with zig-cc due to Golang's implicit
+       // dependency on gcc_s. See issue 59735.
+       b := os.Getenv("GO_BUILDER_NAME")
+       if strings.HasPrefix(b, "linux-") && strings.HasSuffix(b, "-zig-cc") {
+               return false
+       }
+
        return true
 }
 

Run like this:

src$ GO_BUILDER_NAME=linux-amd64-zig-cc CC=zig-cc ./run.bash

Also in https://github.com/motiejus/go/blob/zig-cc-tests/README-zig-cc.md

On linux/arm64 I am getting a very similar error to #59466. I will punt linux/arm64 for now; let's get linux/amd64 going first.