Skip to content

use frame pointer unwinding for Go 1.21+ on aarch64 #422

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
fabled merged 2 commits into from
Apr 17, 2025
Merged

use frame pointer unwinding for Go 1.21+ on aarch64 #422

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
a3c7287
use frame pointer unwinding for Go 1.21+ on aarch64
fabled Mar 29, 2025
db970f3
use type for strategy
fabled Apr 8, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
161 changes: 86 additions & 75 deletions nativeunwind/elfunwindinfo/elfgopclntab.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -11,9 +11,9 @@ import (
"bytes"
"debug/elf"
"fmt"
"go/version"
"unsafe"

log "github.com/sirupsen/logrus"
"go.opentelemetry.io/ebpf-profiler/libpf/pfelf"
sdtypes "go.opentelemetry.io/ebpf-profiler/nativeunwind/stackdeltatypes"
)
Expand Down Expand Up @@ -229,11 +229,13 @@ func getString(data []byte, offset int) []byte {
return data[offset : offset+zeroIdx]
}

type strategy int

const (
strategyUnknown = iota
strategyUnknown strategy = iota
strategyFramePointer
strategyDeltasWithoutRBP
strategyDeltasWithRBP
strategyDeltasWithFrame
strategyDeltasWithoutFrame
)

// noFPSourceSuffixes lists the go runtime source files that call assembly code
Expand All @@ -251,30 +253,24 @@ var noFPSourceSuffixes = [][]byte{
}

// getSourceFileStrategy categorizes sourceFile's unwinding strategy based on its name
func getSourceFileStrategy(arch elf.Machine, sourceFile []byte) int {
func getSourceFileStrategy(arch elf.Machine, sourceFile []byte, defaultStrategy strategy) strategy {
switch arch {
case elf.EM_X86_64:
// Most of the assembly code needs explicit SP delta as they do not
// create stack frame. Do not recover RBP as it is not modified.
if bytes.HasSuffix(sourceFile, []byte(".s")) {
return strategyDeltasWithoutRBP
return strategyDeltasWithoutFrame
}

// Check for the Go source files needing SP delta unwinding to recover RBP
for _, suffix := range noFPSourceSuffixes {
if bytes.HasSuffix(sourceFile, suffix) {
return strategyDeltasWithRBP
return strategyDeltasWithFrame
}
}
case elf.EM_AARCH64:
// Assume all code has frame pointers as the code generated by Golang compiler
// for ARM64 supports frame pointers even for asm code. Frame pointers
// get omitted only for leaf, no arg functions.
return strategyFramePointer
return defaultStrategy
default:
return defaultStrategy
}

// Use frame pointer for others
return strategyFramePointer
}

// SearchGoPclntab uses heuristic to find the gopclntab from RO data.
Expand Down Expand Up @@ -474,10 +470,37 @@ func (ee *elfExtractor) parseGoPclntab() error {
// would fill up our precious kernel delta maps fast, the strategy is to
// create deltastack maps for non-Go source files only, and otherwise
// cover the vast majority with "use frame pointer" stack delta.
sourceStrategy := make(map[int]int)
sourceStrategy := make(map[int]strategy)

// Get target machine architecture for the ELF file
arch := ef.Machine
defaultStrategy := strategyFramePointer
var parsePclntab func(*sdtypes.StackDeltaArray, *pclntabFunc, uintptr, []byte,
strategy, uint64, uint8) error

switch arch {
case elf.EM_X86_64:
parsePclntab = parseX86pclntabFunc
case elf.EM_AARCH64:
parsePclntab = parseArm64pclntabFunc
// Go 1.20 and earlier did not maintain frame pointers properly on arm64.
// This was fixed for Go 1.21 and later in:
// https://github.com/golang/go/commit/a41a29ad19c25c3475a65b7265fcad870d954c2a
switch hdr.magic {
case magicGo1_2, magicGo1_16, magicGo1_18:
// Magic indicates old Go with broken arm64 frame pointers
defaultStrategy = strategyDeltasWithFrame
case magicGo1_20:
// Ambiguous regarding if frame pointer is kept correctly.
// Take the slow path of resolving Go version.
goVer, err := ee.file.GoVersion()
if err != nil || version.Compare(goVer, "go1.21rc1") < 0 {
Copy link
Copy Markdown
Member

@florianl florianl Apr 10, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Nit: Release candidates are for temporary testing. Maybe we can just use the first release with this change in Go:

Suggested change
if err != nil || version.Compare(goVer, "go1.21rc1") < 0 {
if err != nil || version.Compare(goVer, "go1.21.0") < 0 {

Copy link
Copy Markdown
Contributor Author

@fabled fabled Apr 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I have a strong preference to keep the actual first rc tag here. The Go libraries support comparing versions with them, and this makes the code work with the prerelease tags. This also serves as note to remind what is the first tag when the Golang change was made.

defaultStrategy = strategyDeltasWithFrame
}
}
default:
return fmt.Errorf("unsupported ELF architecture (%x)", arch)
}

fmap := &pclntabFuncMap{}
fun := &pclntabFunc{}
Expand Down Expand Up @@ -526,7 +549,7 @@ func (ee *elfExtractor) parseGoPclntab() error {

// Use source file to determine strategy if possible, and default
// to using frame pointers in the unlikely case of no file info
strategy := strategyFramePointer
fileStrategy := defaultStrategy
if fun.pcfileOff != 0 {
p := newPcval(pctab[fun.pcfileOff:], uint(fun.startPc), hdr.quantum)
fileIndex := int(p.val)
Expand All @@ -535,25 +558,25 @@ func (ee *elfExtractor) parseGoPclntab() error {
}

// Determine strategy
strategy = sourceStrategy[fileIndex]
if strategy == strategyUnknown {
fileStrategy = sourceStrategy[fileIndex]
if fileStrategy == strategyUnknown {
sourceFile := getString(filetab, getInt32(cutab, 4*fileIndex))
strategy = getSourceFileStrategy(arch, sourceFile)
sourceStrategy[fileIndex] = strategy
fileStrategy = getSourceFileStrategy(arch, sourceFile, defaultStrategy)
sourceStrategy[fileIndex] = fileStrategy
}
}

switch arch {
case elf.EM_X86_64:
if err := parseX86pclntabFunc(ee.deltas, fun, dataLen, pctab, strategy, i,
hdr.quantum); err != nil {
return err
}
case elf.EM_AARCH64:
if err := parseArm64pclntabFunc(ee.deltas, fun, dataLen, pctab, i,
hdr.quantum); err != nil {
return err
}
if fileStrategy == strategyFramePointer {
// Use stack frame-pointer delta
ee.deltas.Add(sdtypes.StackDelta{
Address: fun.startPc,
Info: sdtypes.UnwindInfoFramePointer,
})
continue
}
if err := parsePclntab(ee.deltas, fun, dataLen, pctab, fileStrategy, i,
hdr.quantum); err != nil {
return err
}
}

Expand Down Expand Up @@ -587,48 +610,41 @@ func (ee *elfExtractor) parseGoPclntab() error {

// parseX86pclntabFunc extracts interval information from x86_64 based pclntabFunc.
func parseX86pclntabFunc(deltas *sdtypes.StackDeltaArray, fun *pclntabFunc, dataLen uintptr,
pctab []byte, strategy int, i uint64, quantum uint8) error {
switch {
case strategy == strategyFramePointer:
// Use stack frame-pointer delta
deltas.Add(sdtypes.StackDelta{
Address: fun.startPc,
Info: sdtypes.UnwindInfoFramePointerX64,
})
pctab []byte, s strategy, i uint64, quantum uint8) error {
if fun.pcspOff == 0 {
// Some functions don't have PCSP info: skip them.
return nil
case fun.pcspOff != 0:
// Generate stack deltas as the information is available
if dataLen < uintptr(fun.pcspOff) {
return fmt.Errorf(".gopclntab func %v pcscOff (%d) is invalid",
i, fun.pcspOff)
}
}
// Generate stack deltas as the information is available
if dataLen < uintptr(fun.pcspOff) {
return fmt.Errorf(".gopclntab func %v pcscOff (%d) is invalid",
i, fun.pcspOff)
}

p := newPcval(pctab[fun.pcspOff:], uint(fun.startPc), quantum)
hints := sdtypes.UnwindHintKeep
for ok := true; ok; ok = p.step() {
info := sdtypes.UnwindInfo{
Opcode: sdtypes.UnwindOpcodeBaseSP,
Param: p.val + 8,
}
if strategy == strategyDeltasWithRBP && info.Param >= 16 {
info.FPOpcode = sdtypes.UnwindOpcodeBaseCFA
info.FPParam = -16
}
deltas.Add(sdtypes.StackDelta{
Address: uint64(p.pcStart),
Hints: hints,
Info: info,
})
hints = sdtypes.UnwindHintNone
p := newPcval(pctab[fun.pcspOff:], uint(fun.startPc), quantum)
hints := sdtypes.UnwindHintKeep
for ok := true; ok; ok = p.step() {
info := sdtypes.UnwindInfo{
Opcode: sdtypes.UnwindOpcodeBaseSP,
Param: p.val + 8,
}
if s == strategyDeltasWithFrame && info.Param >= 16 {
info.FPOpcode = sdtypes.UnwindOpcodeBaseCFA
info.FPParam = -16
}
deltas.Add(sdtypes.StackDelta{
Address: uint64(p.pcStart),
Hints: hints,
Info: info,
})
hints = sdtypes.UnwindHintNone
}
log.Debugf("Unhandled .gopclntab func at %d", i)
return nil
}

// parseArm64pclntabFunc extracts interval information from ARM64 based pclntabFunc.
func parseArm64pclntabFunc(deltas *sdtypes.StackDeltaArray, fun *pclntabFunc,
dataLen uintptr, pctab []byte, i uint64, quantum uint8) error {
dataLen uintptr, pctab []byte, s strategy, i uint64, quantum uint8) error {
if fun.pcspOff == 0 {
// Some CGO functions don't have PCSP info: skip them.
return nil
Expand All @@ -637,13 +653,6 @@ func parseArm64pclntabFunc(deltas *sdtypes.StackDeltaArray, fun *pclntabFunc,
return fmt.Errorf(".gopclntab func %v pcspOff = %d is invalid", i, fun.pcspOff)
}

// On ARM64, frame pointers are not properly kept when the Go runtime copies the stack during
// `runtime.morestack` calls: all old frame pointers are set to 0.
//
// https://github.com/golang/go/blob/c318f191/src/runtime/stack.go#L676
//
// We thus need to unwind with stack delta offsets.

hint := sdtypes.UnwindHintKeep
p := newPcval(pctab[fun.pcspOff:], uint(fun.startPc), quantum)
for ok := true; ok; ok = p.step() {
Expand All @@ -657,9 +666,11 @@ func parseArm64pclntabFunc(deltas *sdtypes.StackDeltaArray, fun *pclntabFunc,
// Unwind via SP offset.
Opcode: sdtypes.UnwindOpcodeBaseSP,
Param: p.val,
}
if s == strategyDeltasWithFrame {
// On ARM64, the previous LR value is stored to top-of-stack.
FPOpcode: sdtypes.UnwindOpcodeBaseSP,
FPParam: 0,
info.FPOpcode = sdtypes.UnwindOpcodeBaseSP
info.FPParam = 0
}
}

Expand Down
12 changes: 6 additions & 6 deletions nativeunwind/elfunwindinfo/elfgopclntab_test.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -53,16 +53,16 @@ func TestPcvalInvalid(_ *testing.T) {
// Some strategy tests
func TestGoStrategy(t *testing.T) {
res := []struct {
file string
strategy int
file string
result strategy
}{
{"foo.go", strategyFramePointer},
{"foo.s", strategyDeltasWithoutRBP},
{"go/src/crypto/elliptic/p256_asm.go", strategyDeltasWithRBP},
{"foo.s", strategyDeltasWithoutFrame},
{"go/src/crypto/elliptic/p256_asm.go", strategyDeltasWithFrame},
}
for _, x := range res {
s := getSourceFileStrategy(elf.EM_X86_64, []byte(x.file))
assert.Equal(t, x.strategy, s)
s := getSourceFileStrategy(elf.EM_X86_64, []byte(x.file), strategyFramePointer)
assert.Equal(t, x.result, s)
}
}

Expand Down
19 changes: 9 additions & 10 deletions nativeunwind/stackdeltatypes/stackdeltatypes.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -29,10 +29,11 @@ const (
UnwindOpcodeFlagDeref uint8 = C.UNWIND_OPCODEF_DEREF

// UnwindCommands from the C header file
UnwindCommandInvalid int32 = C.UNWIND_COMMAND_INVALID
UnwindCommandStop int32 = C.UNWIND_COMMAND_STOP
UnwindCommandPLT int32 = C.UNWIND_COMMAND_PLT
UnwindCommandSignal int32 = C.UNWIND_COMMAND_SIGNAL
UnwindCommandInvalid int32 = C.UNWIND_COMMAND_INVALID
Copy link
Copy Markdown
Member

@florianl florianl Apr 10, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Maybe we should bring these constants into support/types_def.go - then we don't need to manually keep them in sync. But this can be part of another PR.

Copy link
Copy Markdown
Contributor Author

@fabled fabled Apr 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Sure, will do a follow up PR on this.

UnwindCommandStop int32 = C.UNWIND_COMMAND_STOP
UnwindCommandPLT int32 = C.UNWIND_COMMAND_PLT
UnwindCommandSignal int32 = C.UNWIND_COMMAND_SIGNAL
UnwindCommandFramePointer int32 = C.UNWIND_COMMAND_FRAME_POINTER

// UnwindDeref handling from the C header file
UnwindDerefMask int32 = C.UNWIND_DEREF_MASK
Expand Down Expand Up @@ -63,12 +64,10 @@ var UnwindInfoStop = UnwindInfo{Opcode: UnwindOpcodeCommand, Param: UnwindComman
// UnwindInfoSignal is the stack delta info indicating signal return frame.
var UnwindInfoSignal = UnwindInfo{Opcode: UnwindOpcodeCommand, Param: UnwindCommandSignal}

// UnwindInfoFramePointerX64 contains the description to unwind a x86-64 frame pointer frame.
var UnwindInfoFramePointerX64 = UnwindInfo{
Opcode: UnwindOpcodeBaseFP,
Param: 16,
FPOpcode: UnwindOpcodeBaseCFA,
FPParam: -16,
// UnwindInfoFramePointer contains the description to unwind a frame pointer frame.
var UnwindInfoFramePointer = UnwindInfo{
Opcode: UnwindOpcodeCommand,
Param: UnwindCommandFramePointer,
}

// UnwindInfoLR contains the description to unwind ARM64 function without a frame (LR only)
Expand Down
10 changes: 10 additions & 0 deletions support/ebpf/native_stack_trace.ebpf.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -403,6 +403,11 @@ static ErrorCode unwind_one_frame(u64 pid, u32 frame_idx, UnwindState *state, bo
DEBUG_PRINT("signal frame");
goto frame_ok;
case UNWIND_COMMAND_STOP: *stop = true; return ERR_OK;
case UNWIND_COMMAND_FRAME_POINTER:
if (!unwinder_unwind_frame_pointer(state)) {
goto err_native_pc_read;
}
goto frame_ok;
default: return ERR_UNREACHABLE;
}
} else {
Expand Down Expand Up @@ -485,6 +490,11 @@ static ErrorCode unwind_one_frame(u64 pid, u32 frame_idx, struct UnwindState *st
DEBUG_PRINT("signal frame");
goto frame_ok;
case UNWIND_COMMAND_STOP: *stop = true; return ERR_OK;
case UNWIND_COMMAND_FRAME_POINTER:
if (!unwinder_unwind_frame_pointer(state)) {
goto err_native_pc_read;
}
goto frame_ok;
default: return ERR_UNREACHABLE;
}
}
Expand Down
10 changes: 6 additions & 4 deletions support/ebpf/stackdeltatypes.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17,13 +17,15 @@
#define UNWIND_OPCODEF_DEREF 0x80

// Unsupported or no value for the register
#define UNWIND_COMMAND_INVALID 0
#define UNWIND_COMMAND_INVALID 0
// For CFA: stop unwinding, this function is a stack root function
#define UNWIND_COMMAND_STOP 1
#define UNWIND_COMMAND_STOP 1
// Unwind a PLT entry
#define UNWIND_COMMAND_PLT 2
#define UNWIND_COMMAND_PLT 2
// Unwind a signal frame
#define UNWIND_COMMAND_SIGNAL 3
#define UNWIND_COMMAND_SIGNAL 3
// Unwind using standard frame pointer
#define UNWIND_COMMAND_FRAME_POINTER 4

// If opcode has UNWIND_OPCODEF_DEREF set, the lowest bits of 'param' are used
// as second adder as post-deref operation. This contains the mask for that.
Expand Down
16 changes: 16 additions & 0 deletions support/ebpf/tracemgmt.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -280,6 +280,22 @@ unwinder_mark_nonleaf_frame(UnwindState *state)
#endif
}

// unwinder_unwind_frame_pointer unwinds using the Frame Pointer.
static inline __attribute__((__always_inline__)) bool
unwinder_unwind_frame_pointer(UnwindState *state)
{
unsigned long regs[2];

if (bpf_probe_read_user(regs, sizeof(regs), (void *)state->fp)) {
return false;
}
state->sp = state->fp + sizeof(regs);
state->fp = regs[0];
state->pc = regs[1];
unwinder_mark_nonleaf_frame(state);
return true;
}

// Push the file ID, line number and frame type into FrameList with a user-defined
// maximum stack size.
//
Expand Down
Binary file modified support/ebpf/tracer.ebpf.release.amd64
View file
Open in desktop
Binary file not shown.
Binary file modified support/ebpf/tracer.ebpf.release.arm64
View file
Open in desktop
Binary file not shown.
Loading