From: Jay Conrod <jayconrod@google.com>
Date: Tue, 21 Sep 2021 20:54:58 +0000 (-0700)
Subject: cmd/go: adjust comments on why fuzzing instrumentation is disabled
X-Git-Tag: go1.18beta1~1204
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=d5d3f80013fa9c4fda5ed2fd3d04868dd212ff8d;p=gostls13.git

cmd/go: adjust comments on why fuzzing instrumentation is disabled

For #48504
Related #14565

Change-Id: Ibe43c75224525c4b80dbb66a1b6e0d688e47e2e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/351314
Trust: Jay Conrod <jayconrod@google.com>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
---

diff --git a/src/cmd/go/internal/work/init.go b/src/cmd/go/internal/work/init.go
index 2a605e73ee..34d2e1cbe1 100644
--- a/src/cmd/go/internal/work/init.go
+++ b/src/cmd/go/internal/work/init.go
@@ -60,9 +60,23 @@ func BuildInit() {
 	}
 }
 
+// FuzzInstrumentFlags returns compiler flags that enable fuzzing instrumation
+// on supported platforms. On unsupported platforms, FuzzInstrumentFlags returns
+// nil.
 func FuzzInstrumentFlags() []string {
-	if cfg.Goarch != "amd64" && cfg.Goarch != "arm64" {
-		// Instrumentation is only supported on 64-bit architectures.
+	// TODO: expand the set of supported platforms, with testing.
+	// Nothing about the instrumentation is OS specific, but only amd64 and arm64
+	// are supported in the runtime. See src/runtime/libfuzzer*.
+	//
+	// Keep in sync with build constraints in internal/fuzz/counters_{un,}supported.go
+	switch cfg.Goos {
+	case "darwin", "freebsd", "linux", "windows":
+	default:
+		return nil
+	}
+	switch cfg.Goarch {
+	case "amd64", "arm64":
+	default:
 		return nil
 	}
 	return []string{"-d=libfuzzer"}
diff --git a/src/cmd/go/testdata/script/test_fuzz_cache.txt b/src/cmd/go/testdata/script/test_fuzz_cache.txt
index 8bcf2be61e..a3fcca887e 100644
--- a/src/cmd/go/testdata/script/test_fuzz_cache.txt
+++ b/src/cmd/go/testdata/script/test_fuzz_cache.txt
@@ -1,8 +1,9 @@
 # TODO(jayconrod): support shared memory on more platforms.
 [!darwin] [!linux] [!windows] skip
 
-# TODO(#48504): fix and re-enable.
-[linux] [386] skip
+# Instrumentation not supported on other archs.
+# See #14565.
+[!amd64] [!arm64] skip
 
 [short] skip
 env GOCACHE=$WORK/cache
diff --git a/src/cmd/go/testdata/script/test_fuzz_seed_corpus.txt b/src/cmd/go/testdata/script/test_fuzz_seed_corpus.txt
index f810ad48d9..a66d0554b6 100644
--- a/src/cmd/go/testdata/script/test_fuzz_seed_corpus.txt
+++ b/src/cmd/go/testdata/script/test_fuzz_seed_corpus.txt
@@ -1,8 +1,9 @@
 # TODO(jayconrod): support shared memory on more platforms.
 [!darwin] [!linux] [!windows] skip
 
-# TODO(#48504): fix and re-enable.
-[linux] [386] skip
+# Instrumentation not supported on other archs.
+# See #14565.
+[!amd64] [!arm64] skip
 
 [short] skip
 env GOCACHE=$WORK/cache
diff --git a/src/internal/fuzz/counters_unsupported.go b/src/internal/fuzz/counters_unsupported.go
index 743ef45a66..9595cb93f7 100644
--- a/src/internal/fuzz/counters_unsupported.go
+++ b/src/internal/fuzz/counters_unsupported.go
@@ -7,7 +7,9 @@
 package fuzz
 
 // TODO(#48504): re-enable on platforms where instrumentation works.
-// This was disabled due to an init failure on aix_ppc64.
+// In theory, we shouldn't need this file at all: if the binary was built
+// without coverage, then _counters and _ecounters should have the same address.
+// However, this caused an init failure on aix/ppc64, so it's disabled here.
 
 // coverage returns a []byte containing unique 8-bit counters for each edge of
 // the instrumented source code. This coverage data will only be generated if