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package generate
import (
"fmt"
"strings"
)
func generateBPFHandler(tp GeneratedTracepoint) string {
f := tp.Format
isEnter := strings.Split(f.Name, "_")[1] == "enter"
// Use the kernel's actual tracepoint context structs (syscall_trace_enter/exit)
// rather than the BTF-emitted trace_event_raw_sys_enter/exit aliases. On RHEL 9
// kernels (5.14 with the rt-merge backport that added preempt_lazy_count to
// trace_entry) the two diverge: trace_event_raw_sys_* grows by 8 bytes and
// the args/ret offsets shift, but the real context handed to the BPF program
// is still syscall_trace_*. Reading via the wider alias trips the verifier's
// max_ctx_offset check and the attach fails with EACCES. The two structs are
// identical on non-RHEL kernels, so this is a no-op everywhere else.
ctxStruct := "syscall_trace_exit"
if isEnter {
ctxStruct = "syscall_trace_enter"
}
eventStruct := eventStructName(tp.Classification.Kind)
comment := eventStruct
if tp.Classification.Kind == KindRet {
comment = fmt.Sprintf("%s (%s)", eventStruct, ClassifyRet(f.Name))
}
eventTypeConst := eventTypeConstant(tp.Classification.Kind, isEnter)
extra := generateExtra(tp, isEnter)
return renderHandler(f.Name, ctxStruct, eventStruct, comment, eventTypeConst, extra)
}
func renderHandler(name, ctxStruct, eventStruct, comment, eventTypeConst, extra string) string {
var b strings.Builder
fmt.Fprintf(&b, "/// %s is a struct %s\n", name, comment)
fmt.Fprintf(&b, "SEC(\"tracepoint/syscalls/%s\")\n", name)
fmt.Fprintf(&b, "int handle_%s(struct %s *ctx) {\n", strings.ToLower(name), ctxStruct)
b.WriteString(" __u32 pid, tid;\n")
b.WriteString(" if (filter(&pid, &tid))\n")
b.WriteString(" return 0;\n")
b.WriteString("\n")
fmt.Fprintf(&b, " struct %s *ev = bpf_ringbuf_reserve(&event_map, sizeof(struct %s), 0);\n", eventStruct, eventStruct)
b.WriteString(" if (!ev)\n")
b.WriteString(" return 0;\n")
b.WriteString("\n")
fmt.Fprintf(&b, " ev->event_type = %s;\n", eventTypeConst)
fmt.Fprintf(&b, " ev->trace_id = %s;\n", strings.ToUpper(name))
b.WriteString(" ev->pid = pid;\n")
b.WriteString(" ev->tid = tid;\n")
b.WriteString(" ev->time = bpf_ktime_get_boot_ns();\n")
if extra != "" {
b.WriteString(extra)
}
b.WriteString("\n")
b.WriteString(" bpf_ringbuf_submit(ev, 0);\n")
b.WriteString(" return 0;\n")
b.WriteString("}\n")
return b.String()
}
// generateExtra returns the kind-specific C body lines for a tracepoint handler,
// dispatching to a per-kind helper so that each case stays concise.
func generateExtra(tp GeneratedTracepoint, isEnter bool) string {
f := tp.Format
switch tp.Classification.Kind {
case KindFd:
return generateExtraFd(f)
case KindDup3:
return " ev->fd = (__s32)ctx->args[0];\n ev->flags = (__s32)ctx->args[2];\n"
case KindOpenByHandleAt:
return " ev->flags = (__s32)ctx->args[2];\n"
case KindOpen:
return generateExtraOpen(f)
case KindPathname:
return generateExtraPathname(tp, f)
case KindName:
return generateExtraName(f)
case KindFcntl:
return generateExtraFcntl(f)
case KindRet:
return fmt.Sprintf(" ev->ret = ctx->ret;\n ev->ret_type = %s;\n", ClassifyRet(f.Name))
case KindNull:
return ""
}
return ""
}
// generateExtraFd returns the fd-capture lines for fd-family events.
func generateExtraFd(f *Format) string {
if f.Name == "sys_enter_pidfd_getfd" {
return " ev->fd = (__s32)ctx->args[0];\n"
}
fdIdx := f.FieldNumber("fd")
if fdIdx >= 0 {
return fmt.Sprintf(" ev->fd = (__s32)ctx->args[%d];\n", fdIdx)
}
return " ev->fd = (__s32)ctx->args[0];\n"
}
// generateExtraOpen returns the filename/comm/flags capture lines for open-family events.
func generateExtraOpen(f *Format) string {
filenameIdx := f.FieldNumber("filename")
flagsIdx := f.FieldNumber("flags")
var b strings.Builder
b.WriteString(" __builtin_memset(&(ev->filename), 0, sizeof(ev->filename) + sizeof(ev->comm));\n")
fmt.Fprintf(&b, " bpf_probe_read_user_str(ev->filename, sizeof(ev->filename), (void *)ctx->args[%d]);\n", filenameIdx)
b.WriteString(" bpf_get_current_comm(&ev->comm, sizeof(ev->comm));\n")
if flagsIdx > -1 {
fmt.Fprintf(&b, " ev->flags = ctx->args[%d];\n", flagsIdx)
} else {
b.WriteString(" ev->flags = -1; // Probably OK\n")
}
return b.String()
}
// generateExtraPathname returns the pathname capture lines for path-family events.
func generateExtraPathname(tp GeneratedTracepoint, f *Format) string {
fieldName := tp.Classification.PathnameField
fieldIdx := f.FieldNumber(fieldName)
var b strings.Builder
b.WriteString(" __builtin_memset(&(ev->pathname), 0, sizeof(ev->pathname));\n")
fmt.Fprintf(&b, " bpf_probe_read_user_str(ev->pathname, sizeof(ev->pathname), (void*)ctx->args[%d]);\n", fieldIdx)
return b.String()
}
// generateExtraName returns the oldname/newname capture lines for rename/link-family events.
func generateExtraName(f *Format) string {
oldIdx := f.FieldNumber("oldname")
newIdx := f.FieldNumber("newname")
var b strings.Builder
b.WriteString(" __builtin_memset(&(ev->oldname), 0, sizeof(ev->oldname) + sizeof(ev->newname));\n")
fmt.Fprintf(&b, " bpf_probe_read_user_str(ev->oldname, sizeof(ev->oldname), (void*)ctx->args[%d]);\n", oldIdx)
fmt.Fprintf(&b, " bpf_probe_read_user_str(ev->newname, sizeof(ev->newname), (void*)ctx->args[%d]);\n", newIdx)
return b.String()
}
// generateExtraFcntl returns the fd/cmd/arg capture lines for fcntl events.
func generateExtraFcntl(f *Format) string {
fdIdx := f.FieldNumber("fd")
cmdIdx := f.FieldNumber("cmd")
argIdx := f.FieldNumber("arg")
return fmt.Sprintf(
" ev->fd = ctx->args[%d];\n ev->cmd = ctx->args[%d];\n ev->arg = ctx->args[%d];\n",
fdIdx, cmdIdx, argIdx,
)
}
// eventStructName returns the C struct name for a TracepointKind. The mapping
// is driven by kindRegistry so adding a new kind only requires a registry entry.
func eventStructName(kind TracepointKind) string {
return lookupKind(kind).structName
}
func eventTypeConstant(kind TracepointKind, isEnter bool) string {
prefix := "EXIT_"
if isEnter {
prefix = "ENTER_"
}
return prefix + strings.ToUpper(eventStructName(kind))
}
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