datasec_bug_reproducer.c

// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/* Copyright (c) 2020 Facebook */
#include <stdio.h>
#include <unistd.h>
#include <sys/resource.h>
#include "bpf/libbpf.h"
#include "bpf/btf.h"
#include "assert.h"

static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
{
	return vfprintf(stderr, format, args);
}

int main(int argc, char **argv)
{
	libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
	/* Set up libbpf errors and debug info callback */
	libbpf_set_print(libbpf_print_fn);

	struct btf *btf;
	int ret, myint, myintvar, mydatasec, mystruct, mytypedef, mystructvar;
	
	// This test fails as vars are defined after datasec.
	// Type IDs:
	// 1: datasec
	// 2: mystructvar
	// 3: myintvar
	// 4: mystruct
	// 5: int
	// 6: typedef

	btf = btf__new_empty();
	assert(btf != NULL);

	mydatasec = btf__add_datasec(btf, "mydatasec", 4+4);
	assert(mydatasec > 0);

	ret = btf__add_datasec_var_info(btf, 2, 0, 4);
	assert(ret == 0);

	ret = btf__add_datasec_var_info(btf, 3, 4, 4);
	assert(ret == 0);

	mystructvar = btf__add_var(btf, "mystructvar", BTF_VAR_STATIC, 4);
	assert(mystructvar > 0);

	myintvar = btf__add_var(btf, "myintvar", BTF_VAR_STATIC, 6);
	assert(myintvar > 0);

	mystruct = btf__add_struct(btf, "mystruct", 4);
	assert(mystruct > 0);

	myint = btf__add_int(btf, "myint", 4, 0);
	assert(myint > 0);

	mytypedef = btf__add_typedef(btf, "mytypedef", myint);
	assert(mytypedef > 0);

	ret = btf__load_into_kernel(btf);
	assert(ret == 0);

	printf("all good. enter to exit: ");
	getchar();

	return 0;
}

datasec_works_fine.c

// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/* Copyright (c) 2020 Facebook */
#include <stdio.h>
#include <unistd.h>
#include <sys/resource.h>
#include "bpf/libbpf.h"
#include "bpf/btf.h"
#include "assert.h"

static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
{
	return vfprintf(stderr, format, args);
}

int main(int argc, char **argv)
{
	libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
	/* Set up libbpf errors and debug info callback */
	libbpf_set_print(libbpf_print_fn);

	struct btf *btf;
	int ret, myint, myintvar, mydatasec, mystruct, mytypedef, mystructvar;

	// This test works as vars are defined before datasec.
	// Type IDs:
	// 1: mystructvar
	// 2: myintvar
	// 3: datasec
	// 4: mystruct
	// 5: int
	// 6: typedef

	btf = btf__new_empty();
	assert(btf != NULL);

	mystructvar = btf__add_var(btf, "mystructvar", BTF_VAR_STATIC, 4);
	assert(mystructvar > 0);

	myintvar = btf__add_var(btf, "myintvar", BTF_VAR_STATIC, 6);
	assert(myintvar > 0);

	mydatasec = btf__add_datasec(btf, "mydatasec", 4+4);
	assert(mydatasec > 0);

	ret = btf__add_datasec_var_info(btf, 1, 0, 4);
	assert(ret == 0);

	ret = btf__add_datasec_var_info(btf, 2, 4, 4);
	assert(ret == 0);

	mystruct = btf__add_struct(btf, "mystruct", 4);
	assert(mystruct > 0);

	myint = btf__add_int(btf, "myint", 4, 0);
	assert(myint > 0);

	mytypedef = btf__add_typedef(btf, "mytypedef", myint);
	assert(mytypedef > 0);

	ret = btf__load_into_kernel(btf);
	assert(ret == 0);

	printf("all good. enter to exit: ");
	getchar();

	return 0;
}

typedef_after_pointer.go

package main

import (
	"errors"
	"fmt"
	"os"

	"github.com/cilium/ebpf"
	"github.com/cilium/ebpf/btf"
)

func main() {
	ds := &btf.Datasec{
		Name: "a",
		Size: 8 + 1,
		Vars: []btf.VarSecinfo{
			{
				Size:   8,
				Offset: 0,
				Type: &btf.Var{Name: "a", Type: &btf.Pointer{
					Target: &btf.Void{},
				}},
			},
			{
				Size:   1,
				Offset: 8,
				Type: &btf.Var{
					Name: "c",
					Type: &btf.Typedef{
						Name: "a",
						Type: &btf.Int{Name: "foo", Size: 1},
					},
				},
			},
		},
	}

	s := btf.NewSpec()
	id, err := s.Add(ds)
	if err != nil {
		exit(err)
	}
	fmt.Println("Datasec added with id", id)

	h, err := btf.NewHandle(s)
	var ve *ebpf.VerifierError
	if errors.As(err, &ve) {
		fmt.Printf("%+v\n", ve)
		os.Exit(1)
	}
	if err != nil {
		exit(err)
	}
	h.Close()

	fmt.Println("BTF loaded successfully")
}

func exit(err error) {
	fmt.Println(err)
	os.Exit(1)
}