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|
package generate
import (
"cmp"
"fmt"
"slices"
"strings"
)
// Syscall groups enter+exit formats by syscall name.
type Syscall struct {
Name string
Enter *Format
Exit *Format
}
// GeneratedTracepoint holds a classified format ready for code generation.
type GeneratedTracepoint struct {
Format *Format
Classification ClassificationResult
}
// GenerateTracepointsC produces the full generated_tracepoints.c content from
// concatenated sysfs format data parsed into formats.
func GenerateTracepointsC(formats []Format) string {
syscalls := groupBySyscall(formats)
var b strings.Builder
b.WriteString("// Code generated - don't change manually!\n\n")
var accepted []GeneratedTracepoint
for _, sc := range syscalls {
tracepoints, reason := classifySyscall(sc)
if reason != "" {
fmt.Fprintf(&b, "/// %s\n", reason)
continue
}
accepted = append(accepted, tracepoints...)
}
slices.SortFunc(accepted, func(a, b GeneratedTracepoint) int {
return cmp.Compare(b.Format.ID, a.Format.ID)
})
b.WriteString("\n")
for _, tp := range accepted {
fmt.Fprintf(&b, "#define %s %d\n", strings.ToUpper(tp.Format.Name), tp.Format.ID)
}
b.WriteString("\n")
for _, tp := range accepted {
b.WriteString(generateBPFHandler(tp))
b.WriteString("\n")
}
return b.String()
}
func groupBySyscall(formats []Format) []Syscall {
m := make(map[string]*Syscall)
var order []string
for i := range formats {
f := &formats[i]
parts := strings.SplitN(f.Name, "_", 3)
if len(parts) < 3 {
continue
}
enterExit := parts[1]
what := parts[2]
sc, ok := m[what]
if !ok {
sc = &Syscall{Name: what}
m[what] = sc
order = append(order, what)
}
if enterExit == "enter" {
sc.Enter = f
} else {
sc.Exit = f
}
}
result := make([]Syscall, 0, len(order))
for _, name := range order {
result = append(result, *m[name])
}
return result
}
func classifySyscall(sc Syscall) ([]GeneratedTracepoint, string) {
var enterClass, exitClass ClassificationResult
allCanGenerate := true
if sc.Enter != nil {
enterClass = classifyEnterForGeneration(sc.Enter)
if enterClass.Kind == KindNone {
allCanGenerate = false
}
} else {
allCanGenerate = false
}
if sc.Exit != nil {
exitClass = ClassifyFormat(sc.Exit)
if exitClass.Kind == KindNone {
allCanGenerate = false
}
} else {
allCanGenerate = false
}
if !allCanGenerate {
names := syscallFormatNames(sc)
return nil, fmt.Sprintf("Skipping %s as incomplete or unclassifiable", strings.Join(names, " "))
}
if isEnterRejected(enterClass.Kind) {
names := syscallFormatNames(sc)
return nil, fmt.Sprintf("Ignoring %s as enter-rejected", strings.Join(names, " "))
}
var result []GeneratedTracepoint
if sc.Enter != nil {
result = append(result, GeneratedTracepoint{Format: sc.Enter, Classification: enterClass})
}
// Emit the exit handler only for syscalls that can actually return.
// Noreturn syscalls (exit, exit_group, rt_sigreturn) never return to the
// syscall site, so their sys_exit tracepoint never fires; emitting a handler
// would be dead code in the generated BPF program. We still emit their enter
// handler above.
if sc.Exit != nil && !isNoreturnSyscall(sc.Name) {
result = append(result, GeneratedTracepoint{Format: sc.Exit, Classification: exitClass})
}
return result, ""
}
func classifyEnterForGeneration(f *Format) ClassificationResult {
classification := ClassifyFormat(f)
if classification.Kind != KindNone || len(f.ExternalFields) == 0 {
return classification
}
return ClassificationResult{Kind: KindNull}
}
// isEnterRejected reports whether kind must not appear on a syscall-enter
// tracepoint. The answer comes from the kindRegistry so no switch statement
// needs updating when a new TracepointKind is added.
func isEnterRejected(kind TracepointKind) bool {
return !lookupKind(kind).enterAccepted
}
// noreturnSyscalls lists syscalls that never return to the syscall site.
// Their sys_exit tracepoint can never fire, so the generator suppresses the
// matching exit handler (see classifySyscall) to avoid dead code in the
// generated BPF program, and the enter handler uses the noreturn enter hook
// that skips the (otherwise un-reclaimable) syscall_enter_state_map write.
//
// - exit / exit_group terminate the thread/process; control never returns.
// - rt_sigreturn restores the pre-signal execution context off the signal
// stack frame and resumes the interrupted instruction. It does NOT return
// to the instruction after the rt_sigreturn syscall, so the kernel never
// fires sys_exit_rt_sigreturn. Verified empirically against
// /sys/kernel/tracing: sys_enter_rt_sigreturn fires once per signal-handler
// return while sys_exit_rt_sigreturn never does. The man page (sigreturn(2))
// states plainly that "sigreturn() never returns". rt_sigreturn is emitted
// by the signal trampoline, not called directly by applications.
var noreturnSyscalls = map[string]bool{
"exit": true,
"exit_group": true,
"rt_sigreturn": true,
}
// isNoreturnSyscall reports whether the named syscall never returns and thus
// must not have an exit handler emitted.
func isNoreturnSyscall(name string) bool {
return noreturnSyscalls[name]
}
func syscallFormatNames(sc Syscall) []string {
var names []string
if sc.Enter != nil {
names = append(names, sc.Enter.Name)
}
if sc.Exit != nil {
names = append(names, sc.Exit.Name)
}
slices.Sort(names)
return names
}
|
