On Mon, 2025-02-03 at 16:40 +0000, Mykyta Yatsenko wrote:
> From: Mykyta Yatsenko <yatsenko@xxxxxxxx>
>
> To better verify some complex BPF programs we'd like to preset global
> variables.
> This patch introduces CLI argument `--set-global-vars` to veristat, that
> allows presetting values to global variables defined in BPF program. For
> example:
>
> prog.c:
> ```
> enum Enum { ELEMENT1 = 0, ELEMENT2 = 5 };
> const volatile __s64 a = 5;
> const volatile __u8 b = 5;
> const volatile enum Enum c = ELEMENT2;
> const volatile bool d = false;
>
> char arr[4] = {0};
>
> SEC("tp_btf/sched_switch")
> int BPF_PROG(...)
> {
> bpf_printk("%c\n", arr[a]);
> bpf_printk("%c\n", arr[b]);
> bpf_printk("%c\n", arr[c]);
> bpf_printk("%c\n", arr[d]);
> return 0;
> }
> ```
> By default verification of the program fails:
> ```
> ./veristat prog.bpf.o
> ```
> By presetting global variables, we can make verification pass:
> ```
> ./veristat wq.bpf.o --set-global-vars "a = 0; b = 1; c = 2; d = 3;"
> ```
>
> Signed-off-by: Mykyta Yatsenko <yatsenko@xxxxxxxx>
> ---
This is super useful, thank you!
Maybe also add an ability to read variables list from a file?
(e.g. using -g @file-name syntax as in -f).
Worked fine for my small example, but failed to affect an object file
with multiple programs, see below.
Also, given that it is non-trivial to see if variable had indeed been set,
I think it would be useful to add a selftest that does
system("./veristat -l7 -v -g ...") and matches log output to check that
values are set correctly, e.g. I used the following simple test:
const volatile u8 _u8 = 0;
const volatile u16 _u16 = 0;
const volatile u32 _u32 = 0;
const volatile u64 _u64 = 0;
const volatile s8 _s8 = 0;
const volatile s16 _s16 = 0;
const volatile s32 _s32 = 0;
const volatile s64 _s64 = 0;
SEC("socket")
int test_globals(void *ctx)
{
volatile unsigned long cnt;
cnt = _u8;
cnt = _u16;
cnt = _u32;
cnt = _u64;
cnt = _s8;
cnt = _s16;
cnt = _s32;
cnt = _s64;
return cnt;
}
> tools/testing/selftests/bpf/veristat.c | 189 +++++++++++++++++++++++++
> 1 file changed, 189 insertions(+)
[...]
> @@ -1292,6 +1312,169 @@ static int process_prog(const char *filename, struct bpf_object *obj, struct bpf
> return 0;
> };
>
> +static int parse_var_presets(char *expr, struct var_preset *presets, int capacity, int *size)
> +{
> + char *state;
> + char *next;
> + int i = 0;
> +
> + while ((next = strtok_r(i ? NULL : expr, ";", &state))) {
> + char *eq_ptr = strchr(next, '=');
> + char *name_ptr = next;
> + char *name_end = eq_ptr - 1;
> + char *val_ptr = eq_ptr + 1;
> +
> + if (!eq_ptr)
> + continue;
Nit: error message here?
> +
> + if (i >= capacity) {
> + fprintf(stderr, "Too many global variable presets\n");
> + return -EINVAL;
> + }
> + while (isspace(*name_ptr))
> + ++name_ptr;
> + while (isspace(*name_end))
> + --name_end;
> +
> + *(name_end + 1) = '\0';
> + presets[i].name = strdup(name_ptr);
> + errno = 0;
> + presets[i].value = strtoll(val_ptr, NULL, 10);
Nit: using base of 0 would allow to specify values either as decimals or in hex
(using '0x' prefix).
> + if (errno == ERANGE) {
> + errno = 0;
> + presets[i].value = strtoull(val_ptr, NULL, 10);
> + }
> + if (errno) {
> + fprintf(stderr, "Could not parse integer value %s\n", val_ptr);
> + return -EINVAL;
> + }
> + ++i;
> + }
> + *size = i;
> + return 0;
> +}
> +
> +static bool is_signed_type(const struct btf_type *type)
> +{
> + if (btf_is_int(type))
Nit: enums could be signed as well.
> + return btf_int_encoding(type) & BTF_INT_SIGNED;
> + return true;
> +}
> +
> +static const struct btf_type *var_base_type(const struct btf *btf, const struct btf_type *type)
> +{
> + switch (btf_kind(type)) {
> + case BTF_KIND_VAR:
> + case BTF_KIND_TYPE_TAG:
> + case BTF_KIND_CONST:
> + case BTF_KIND_VOLATILE:
> + case BTF_KIND_RESTRICT:
> + case BTF_KIND_TYPEDEF:
> + case BTF_KIND_DECL_TAG:
> + return var_base_type(btf, btf__type_by_id(btf, type->type));
> + }
> + return type;
> +}
> +
> +static bool is_preset_supported(const struct btf_type *t)
> +{
> + return btf_is_int(t) || btf_is_enum(t) || btf_is_enum64(t);
> +}
> +
> +static int set_global_var(struct bpf_object *obj, struct btf *btf, const struct btf_type *t,
> + struct bpf_map *map, struct btf_var_secinfo *sinfo, long long new_val)
> +{
> + const struct btf_type *base_type;
> + void *ptr;
> + size_t size;
> +
> + base_type = var_base_type(btf, t);
> + if (!is_preset_supported(base_type)) {
> + fprintf(stderr, "Setting global variable for btf kind %d is not supported\n",
> + btf_kind(base_type));
> + return -EINVAL;
> + }
> +
> + /* Check if value fits into the target variable size */
> + if (sinfo->size < sizeof(new_val)) {
> + bool is_signed = is_signed_type(base_type);
> + __u32 unsigned_bits = sinfo->size * 8 - (is_signed ? 1 : 0);
> + long long max_val = 1ll << unsigned_bits;
> +
> + if (new_val >= max_val || new_val < -max_val) {
> + fprintf(stderr,
> + "Variable %s value %lld is out of range [%lld; %lld]\n",
> + btf__name_by_offset(btf, t->name_off), new_val,
> + is_signed ? -max_val : 0, max_val - 1);
> + return -EINVAL;
> + }
> + }
> +
> + ptr = (void *)bpf_map__initial_value(map, &size);
> + if (!ptr || (sinfo->offset + sinfo->size > size))
> + return -EINVAL;
> +
> + memcpy(ptr + sinfo->offset, &new_val, sinfo->size);
will this work for big endian?
> + return 0;
> +}
> +
> +static int set_global_vars(struct bpf_object *obj, struct var_preset *presets, int npresets)
> +{
> + struct btf_var_secinfo *sinfo;
> + const char *sec_name;
> + const struct btf_type *type;
> + struct bpf_map *map;
> + struct btf *btf;
> + int i, j, k, n, cnt, err, preset_cnt = 0;
> +
> + if (npresets == 0)
> + return 0;
> +
> + btf = bpf_object__btf(obj);
> + if (!btf)
> + return -EINVAL;
> +
> + cnt = btf__type_cnt(btf);
> + for (i = 0; i != cnt; ++i) {
> + type = btf__type_by_id(btf, i);
> +
> + if (!btf_is_datasec(type))
> + continue;
> +
> + sinfo = btf_var_secinfos(type);
> + sec_name = btf__name_by_offset(btf, type->name_off);
> + map = bpf_object__find_map_by_name(obj, sec_name);
> + if (!map)
> + continue;
> +
> + n = btf_vlen(type);
> + for (j = 0; j < n; ++j, ++sinfo) {
> + const struct btf_type *var_type = btf__type_by_id(btf, sinfo->type);
> + const char *var_name = btf__name_by_offset(btf, var_type->name_off);
> +
> + if (!btf_is_var(var_type))
> + continue;
> +
> + for (k = 0; k < npresets; ++k) {
> + if (strcmp(var_name, presets[k].name) != 0)
> + continue;
> +
> + err = set_global_var(obj, btf, var_type, map, sinfo,
> + presets[k].value);
> + if (err)
> + return err;
> +
> + preset_cnt++;
> + break;
> + }
> + }
> + }
> + if (preset_cnt != npresets)
> + fprintf(stderr, "Some global variable presets have not been applied\n");
Nit: it would be nice to print which ones were not set.
> +
> + return 0;
> +}
> +
> static int process_obj(const char *filename)
> {
> const char *base_filename = basename(strdupa(filename));
> @@ -1338,6 +1521,12 @@ static int process_obj(const char *filename)
> prog_cnt++;
> }
>
> + err = set_global_vars(obj, env.presets, env.npresets);
> + if (err) {
> + fprintf(stderr, "Failed to set global variables\n");
> + goto cleanup;
> + }
> +
> if (prog_cnt == 1) {
> prog = bpf_object__next_program(obj, NULL);
> bpf_program__set_autoload(prog, true);
Same needs to happen for the loop below when prog_cnt != 1, e.g.:
@@ -1544,6 +1544,12 @@ static int process_obj(const char *filename)
goto cleanup;
}
+ err = set_global_vars(tobj, env.presets, env.npresets);
+ if (err) {
+ fprintf(stderr, "Failed to set global variables\n");
+ goto cleanup;
+ }
+
lprog = NULL;
bpf_object__for_each_program(tprog, tobj) {
const char *tprog_name = bpf_program__name(tprog);
Or, better yet, get rid of the `prog_cnt == 1` special case.
