runtime: consider core PID in gdb test

Add the PID to the core file name if the current system uses it
when generating core files.

Fixes #61487

Change-Id: I3b53a6c850c754795c8022921160f03c588d4c91
Reviewed-on: https://go-review.googlesource.com/c/go/+/511659
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@golang.org>

src/runtime/runtime-gdb_unix_test.go

@@ -8,6 +8,7 @@ package runtime_test
 
 import (
 	"bytes"
+	"fmt"
 	"internal/testenv"
 	"io"
 	"os"
@@ -102,6 +103,18 @@ func TestGdbCoreSignalBacktrace(t *testing.T) {
 		t.Skipf("Unexpected core pattern %q", string(b))
 	}
 
+	coreUsesPID := false
+	b, err = os.ReadFile("/proc/sys/kernel/core_uses_pid")
+	if err == nil {
+		switch string(bytes.TrimSpace(b)) {
+		case "0":
+		case "1":
+			coreUsesPID = true
+		default:
+			t.Skipf("unexpected core_uses_pid value %q", string(b))
+		}
+	}
+
 	dir := t.TempDir()
 
 	// Build the source code.
@@ -136,6 +149,8 @@ func TestGdbCoreSignalBacktrace(t *testing.T) {
 	}
 	w.Close()
 
+	pid := cmd.Process.Pid
+
 	// Wait for child to be ready.
 	var buf [1]byte
 	if _, err := r.Read(buf[:]); err != io.EOF {
@@ -167,12 +182,17 @@ func TestGdbCoreSignalBacktrace(t *testing.T) {
 		t.Fatalf("CoreDump got %v want true", ws.CoreDump())
 	}
 
+	coreFile := "core"
+	if coreUsesPID {
+		coreFile += fmt.Sprintf(".%d", pid)
+	}
+
 	// Execute gdb commands.
 	args := []string{"-nx", "-batch",
 		"-iex", "add-auto-load-safe-path " + filepath.Join(testenv.GOROOT(t), "src", "runtime"),
 		"-ex", "backtrace",
 		filepath.Join(dir, "a.exe"),
-		filepath.Join(dir, "core"),
+		filepath.Join(dir, coreFile),
 	}
 	cmd = testenv.Command(t, "gdb", args...)