X Consisteny checks via link failures work

go/xcommon/tracing/cmd/gotrace/gotrace.go

@@ -512,6 +512,13 @@ var traceEventImportTmpl = template.Must(template.New("traceimport").Parse(`
 func {{.ImportSpec.PkgName}}_{{.Name}}_Attach(*tracing.ProbeGroup, func({{.ArgvTypedRelativeTo .ImporterPkg .ImportedAs}})) *tracing.Probe
 `))
 
+// traceEventImportCheckTmpl is code template generated to check consistency with one imported package
+var traceEventImportCheckTmpl = template.Must(template.New("traceimportcheck").Parse(`
+//go:linkname {{.ImportSpec.PkgName}}_trace_exporthash {{.ImportSpec.PkgPath}}._trace_exporthash_{{.ExportHash}}
+func {{.ImportSpec.PkgName}}_trace_exporthash()
+func init() { {{.ImportSpec.PkgName}}_trace_exporthash() } // rerun "gotrace gen" if you see link failure here
+`))
+
 // magic begins all files generated by gotrace
 const magic = "// Code generated by lab.nexedi.com/kirr/go123/tracing/cmd/gotrace; DO NOT EDIT.\n"
 
@@ -744,15 +751,6 @@ func tracegen1(P *Program, tpkg *Package, pkgdir string, kind string) error {
 
 		text := &Buffer{}
 
-		// export hash symbol so that if importing package is out of
-		// sync - it will have it different and linking will fail.
-		if len(tpkg.Eventv) > 0 {
-			//text.emit("\n---- 8< ---- (export signature)")
-			//fmt.Fprintf(text, "%s", traceExport(tpkg, kind))
-			//text.emit("---- 8< ----")
-			text.emit("\nvar _t_exporthash_%s bool", traceExportHash(tpkg, kind))
-		}
-
 		// code for trace:event definitions
 		for _, event := range tpkg.Eventv {
 			needPkg.Add(event.NeedPkgv()...)
@@ -762,6 +760,16 @@ func tracegen1(P *Program, tpkg *Package, pkgdir string, kind string) error {
 			}
 		}
 
+		// export hash symbol so that if importing package is out of
+		// sync - it will have it different and linking will fail.
+		if len(tpkg.Eventv) > 0 {
+			text.emit("\n// trace export signature")
+			//text.emit("---- 8< ----")
+			//fmt.Fprintf(text, "%s", traceExport(tpkg, kind))
+			//text.emit("---- 8< ----")
+			text.emit("func _trace_exporthash_%s() {}", traceExportHash(tpkg, kind))
+		}
+
 		// code for trace:import imports
 		for _, timport := range tpkg.Importv {
 			text.emit("\n// traceimport: %s", timport.ImportSpec())
@@ -787,13 +795,20 @@ func tracegen1(P *Program, tpkg *Package, pkgdir string, kind string) error {
 				return fmt.Errorf("%v: package %v does not export anything trace-related", timport.Pos, timport.PkgPath)
 			}
 
-			// verify export hash
-			text.emit("\nzzz_t_exporthash_%s", traceExportHash(impPkg, ""/*regular pkg*/))
+			// verify export hash so link fails if it gets out of sync with imported package
+			err = traceEventImportCheckTmpl.Execute(text, struct{
+							ImportSpec *traceImport
+							ExportHash string}{
+						timport,
+						traceExportHash(impPkg, ""/*regular package*/)})
+
+			text.emit("")
 
+			// import individual events
 			for _, event := range impPkg.Eventv {
 				needPkg.Add(event.NeedPkgv()...)
 				importedEvent := traceImported{
-					traceEvent: event,
+					traceEvent:	event,
 					ImportSpec:	timport,
 					ImporterPkg:	tpkg.Pkgi.Pkg,
 					ImportedAs:	importedAs,

go/xcommon/tracing/cmd/gotrace/testdata/src/a/pkg1/pkg1c.go

@@ -16,6 +16,6 @@ import "C"
 //trace:event traceHello()
 
 func Hello() {
-	traceHello()
+	//traceHello()
 	C.hello()
 }

go/xcommon/tracing/cmd/gotrace/testdata/src/a/pkg1/ztrace.go.ok

@@ -117,3 +117,6 @@ func traceURLParsed_Attach(pg *tracing.ProbeGroup, probe func(u *url.URL)) *trac
 	tracing.AttachProbe(pg, (**tracing.Probe)(unsafe.Pointer(&_traceURLParsed)), &p.Probe)
 	return &p.Probe
 }
+
+// trace export signature
+func _trace_exporthash_965fa599dc3a61119faba1eacf8493973c5d87ad() {}

go/xcommon/tracing/cmd/gotrace/testdata/src/b/pkg2/ztrace.go.ok

@@ -38,8 +38,16 @@ func traceDoSomething_Attach(pg *tracing.ProbeGroup, probe func(i, j int, q stri
 	return &p.Probe
 }
 
+// trace export signature
+func _trace_exporthash_80ddfc2f6c72bdf357dedbb2f0bbec85e93106fc() {}
+
 // traceimport: "a/pkg1"
 
+//go:linkname pkg1_trace_exporthash a/pkg1._trace_exporthash_965fa599dc3a61119faba1eacf8493973c5d87ad
+func pkg1_trace_exporthash()
+func init() { pkg1_trace_exporthash() } // rerun "gotrace gen" if you see link failure here
+
+
 //go:linkname pkg1_traceDoSomething_Attach a/pkg1.traceDoSomething_Attach
 func pkg1_traceDoSomething_Attach(*tracing.ProbeGroup, func(topic string)) *tracing.Probe
 

go/xcommon/tracing/cmd/gotrace/testdata/src/c/pkg3/ztrace_test.go.ok

@@ -13,6 +13,11 @@ import (
 
 // traceimport: aaa1 "a/pkg1"
 
+//go:linkname aaa1_trace_exporthash a/pkg1._trace_exporthash_965fa599dc3a61119faba1eacf8493973c5d87ad
+func aaa1_trace_exporthash()
+func init() { aaa1_trace_exporthash() } // rerun "gotrace gen" if you see link failure here
+
+
 //go:linkname aaa1_traceDoSomething_Attach a/pkg1.traceDoSomething_Attach
 func aaa1_traceDoSomething_Attach(*tracing.ProbeGroup, func(topic string)) *tracing.Probe
 

go/xcommon/tracing/cmd/gotrace/testdata/src/c/pkg3/ztrace_x_test.go.ok

@@ -10,5 +10,10 @@ import (
 
 // traceimport: "b/pkg2"
 
+//go:linkname pkg2_trace_exporthash b/pkg2._trace_exporthash_80ddfc2f6c72bdf357dedbb2f0bbec85e93106fc
+func pkg2_trace_exporthash()
+func init() { pkg2_trace_exporthash() } // rerun "gotrace gen" if you see link failure here
+
+
 //go:linkname pkg2_traceDoSomething_Attach b/pkg2.traceDoSomething_Attach
 func pkg2_traceDoSomething_Attach(*tracing.ProbeGroup, func(i, j int, q string)) *tracing.Probe