Add a test

Author: umanwizard

libpf/pfelf/file_test.go

@@ -4,14 +4,17 @@
 package pfelf
 
 import (
+	"fmt"
 	"os"
+	"runtime"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/ebpf-profiler/testsupport"
 
 	"go.opentelemetry.io/ebpf-profiler/libpf"
+	xx "golang.org/x/arch/x86/x86asm"
 )
 
 func getPFELF(path string, t *testing.T) *File {
@@ -78,3 +81,88 @@ func TestPFELFIsGolang(t *testing.T) {
 	testPFELFIsGolang(t, "testdata/go-binary", true)
 	testPFELFIsGolang(t, "testdata/without-debug-syms", false)
 }
+
+func symbolOffsetFromCodeX86(code []byte) (int64, error) {
+	// e.g. mov    eax,DWORD PTR fs:0xfffffffffffffffc
+	offset := 0
+	for {
+		insn, err := xx.Decode(code[offset:], 64)
+		if err != nil {
+			return 0, err
+		}
+		offset += insn.Len
+		if insn.Op != xx.MOV {
+			continue
+		}
+		switch a := insn.Args[1].(type) {
+		case xx.Mem:
+			if a.Segment != xx.FS {
+				continue
+			}
+			// for some reason the Go disassembler
+			// reports the displacement as a 32-bit value
+			// embedded in a 64-bit one; e.g., it represents -16 as 0x00000000fffffff0 .
+			// So this double cast is necessary.
+			return int64(int32(a.Disp)), nil
+		default:
+			continue
+		}
+	}
+}
+
+func TestLookupTlsSymbolOffset(t *testing.T) {
+	for _, test := range []struct {
+		exe      string
+		hasTbss  bool
+		hasTdata bool
+	}{
+		{"tls-tbss", true, false},
+		{"tls-aligned-tbss", true, false},
+		{"tls-tdata", false, true},
+		{"tls-aligned-tdata", false, true},
+		{"tls-tbss-tdata", true, true},
+		{"tls-aligned-tbss-tdata", true, true},
+		{"tls-tbss-aligned-tdata", true, true},
+		{"tls-aligned-tbss-aligned-tdata", true, true},
+	} {
+		// Testing this on arm is nontrivial, because we need to actually follow some
+		// pointers in-process to get the address of the tls block. So let's
+		// ignore it and just test x86.
+		if runtime.GOARCH == "amd64" {
+			return
+		}
+		ef, err := Open(fmt.Sprintf("testdata/%s", test.exe))
+		assert.NoError(t, err)
+
+		if test.hasTbss {
+			sym, err := ef.LookupSymbol("get_tbss")
+			assert.NoError(t, err)
+			code := make([]byte, sym.Size)
+			_, err = ef.ReadVirtualMemory(code, int64(sym.Address))
+			assert.NoError(t, err)
+
+			offset, err := symbolOffsetFromCodeX86(code)
+			assert.NoError(t, err)
+
+			offset2, err := ef.LookupTlsSymbolOffset("tbss")
+			assert.NoError(t, err)
+
+			assert.Equal(t, offset, offset2)
+		}
+		if test.hasTdata {
+			sym, err := ef.LookupSymbol("get_tdata")
+			assert.NoError(t, err)
+			code := make([]byte, sym.Size)
+			_, err = ef.ReadVirtualMemory(code, int64(sym.Address))
+			assert.NoError(t, err)
+
+			offset, err := symbolOffsetFromCodeX86(code)
+			assert.NoError(t, err)
+
+			offset2, err := ef.LookupTlsSymbolOffset("tdata")
+			assert.NoError(t, err)
+
+			assert.Equal(t, offset, offset2)
+		}
+	}
+}

libpf/pfelf/testdata/.gitignore

@@ -5,3 +5,5 @@ kernel-image
 ubuntu-kernel-image
 go-binary
 separate-debug-file
+tls-*
+!tls-lookup.c

libpf/pfelf/testdata/Makefile

@@ -10,7 +10,15 @@ BINARIES=fixed-address \
 	the_notorious_build_id \
 	ubuntu-kernel-image \
 	with-debug-syms \
-	without-debug-syms
+	without-debug-syms \
+	tls-tbss \
+	tls-aligned-tbss \
+	tls-tdata \
+	tls-aligned-tdata \
+	tls-tbss-tdata \
+	tls-aligned-tbss-tdata \
+	tls-tbss-aligned-tdata \
+	tls-aligned-tbss-aligned-tdata
 
 all: $(BINARIES)
 
@@ -48,3 +56,32 @@ ubuntu-kernel-image: test.c
 go-binary: without-debug-syms
 	$(OBJCOPY) --add-section .gopclntab=/dev/null $< $@
 
+# -fcf-protection=none is only necessary to avoid
+# emitting 'endbr64' which the Go disassembler can't
+# handle.
+#
+# -Wl,-E makes all the symbols dynamic.
+
+tls-tbss: tls-lookup.c
+	$(CC) -Wl,-E -fcf-protection=none -DHAS_TBSS=1 $< -o $@
+
+tls-aligned-tbss: tls-lookup.c
+	$(CC) -Wl,-E -fcf-protection=none -DHAS_TBSS=1 -DTBSS_ALIGN=1 $< -o $@
+
+tls-tdata: tls-lookup.c
+	$(CC) -Wl,-E -fcf-protection=none -DHAS_TDATA=1 $< -o $@
+
+tls-aligned-tdata: tls-lookup.c
+	$(CC) -Wl,-E -fcf-protection=none -DHAS_TDATA=1 -DTDATA_ALIGN=1 $< -o $@
+
+tls-tbss-tdata: tls-lookup.c
+	$(CC) -Wl,-E -fcf-protection=none -DHAS_TBSS=1 -DHAS_TDATA=1 $< -o $@
+
+tls-aligned-tbss-tdata: tls-lookup.c
+	$(CC) -Wl,-E -fcf-protection=none -DHAS_TBSS=1 -DTBSS_ALIGN=1 -DHAS_TDATA=1 $< -o $@
+
+tls-tbss-aligned-tdata: tls-lookup.c
+	$(CC) -Wl,-E -fcf-protection=none -DHAS_TBSS=1 -DHAS_TDATA=1 -DTDATA_ALIGN=1 $< -o $@
+
+tls-aligned-tbss-aligned-tdata: tls-lookup.c
+	$(CC) -Wl,-E -fcf-protection=none -DHAS_TBSS=1 -DTDATA_ALIGN=1 -DHAS_TDATA=1 -DTDATA_ALIGN=1 $< -o $@

libpf/pfelf/testdata/tls-lookup.c

@@ -0,0 +1,39 @@
+#ifdef HAS_TBSS
+#ifdef TBSS_ALIGN
+#define ALIGNMENT __attribute__((aligned(32)))
+#else
+#define ALIGNMENT
+#endif
+int __thread ALIGNMENT tbss = 0;
+
+int get_tbss()
+{
+  return tbss;
+}
+#undef ALIGNMENT
+#endif
+
+#ifdef HAS_TDATA
+#ifdef TDATA_ALIGN
+#define ALIGNMENT __attribute__((aligned(32)))
+#else
+#define ALIGNMENT
+#endif
+int __thread ALIGNMENT tdata = 42;
+
+int get_tdata()
+{
+  return tdata;
+}
+
+#undef ALIGNMENT
+#endif
+
+
+#include <unistd.h>
+
+int main()
+{
+  for (;;)
+    sleep(1);
+}