Debug: add cgo symbolizer (#5255)

* Add cgo_symbolizer config

* Add comment

* use import block

.bazelrc

@@ -39,6 +39,12 @@ build:release --compilation_mode=opt
 build:llvm --crosstool_top=@llvm_toolchain//:toolchain
 build:llvm --define compiler=llvm
 
+# Build binary with cgo symbolizer for debugging / profiling.
+build:cgo_symbolizer --config=llvm
+build:cgo_symbolizer --copt=-g
+build:cgo_symbolizer --define=USE_CGO_SYMBOLIZER=true
+build:cgo_symbolizer -c dbg
+
 # multi-arch cross-compiling toolchain configs:
 -----------------------------------------------
 build:cross --crosstool_top=@prysm_toolchains//:multiarch_toolchain

.gitignore

@@ -17,6 +17,7 @@ bazel-*
 # Coverage outputs
 coverage.txt
 profile.out
+profile.grind
 
 # Nodejs
 node_modules

WORKSPACE

@@ -1649,3 +1649,10 @@ go_repository(
 load("@com_github_prysmaticlabs_prombbolt//:repositories.bzl", "prombbolt_dependencies")
 
 prombbolt_dependencies()
+
+go_repository(
+    name = "com_github_ianlancetaylor_cgosymbolizer",
+    importpath = "github.com/ianlancetaylor/cgosymbolizer",
+    sum = "h1:GWsU1WjSE2rtvyTYGcndqmPPkQkBNV7pEuZdnGtwtu4=",
+    version = "v0.0.0-20200321040036-d43e30eacb43",
+)

shared/debug/BUILD.bazel

@@ -1,11 +1,20 @@
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
+config_setting(
+    name = "use_cgosymbolizer",
+    values = {"define": "USE_CGO_SYMBOLIZER=true"},
+)
+
+# gazelle:ignore cgo_symbolizer.go
 go_library(
     name = "go_default_library",
     srcs = [
         "debug.go",
         "maxprocs_metric.go",
-    ],
+    ] + select({
+        ":use_cgosymbolizer": ["cgo_symbolizer.go"],
+        "//conditions:default": [],
+    }),
     importpath = "github.com/prysmaticlabs/prysm/shared/debug",
     visibility = ["//visibility:public"],
     deps = [
@@ -14,5 +23,8 @@ go_library(
         "@com_github_prometheus_client_golang//prometheus/promauto:go_default_library",
         "@com_github_sirupsen_logrus//:go_default_library",
         "@in_gopkg_urfave_cli_v2//:go_default_library",
-    ],
+    ] + select({
+        ":use_cgosymbolizer": ["@com_github_ianlancetaylor_cgosymbolizer//:go_default_library"],
+        "//conditions:default": [],
+    }),
 )

shared/debug/cgo_symbolizer.go

@@ -0,0 +1,8 @@
+package debug
+
+import (
+	// Using this file with this imported library configures the process to
+	// expose cgo symbols when possible. Use --config=cgo_symbolizer to make use of
+	// this feature.
+	_ "github.com/ianlancetaylor/cgosymbolizer"
+)