Re: [PATCH bpf-next v2 1/2] selftests/bpf: implement setting global variables in veristat

[Eduard Zingerman <eddyz87@gmail.com>]

On Mon, 2025-02-10 at 13:51 +0000, Mykyta Yatsenko wrote:

[...]

> @@ -363,6 +378,24 @@ static error_t parse_arg(int key, char *arg, struct argp_state *state)
>  			return -ENOMEM;
>  		env.filename_cnt++;
>  		break;
> +	case 'G': {
> +		static int presets_cap;
> +		char *expr = strdup(arg);
> +
> +		if (expr[0] == '@') {
> +			if (parse_var_presets_from_file(expr + 1, &env.presets,
> +							&presets_cap, &env.npresets)) {

Nit: I'd modify 'env' directly in parse_var_presets{,_from_file} and
     add presets_cap field to 'env': to avoid static variable and to
     avoid '(*presets)[*size].name = ...' below.

> +				fprintf(stderr, "Could not parse global variables preset: %s\n",
> +					arg);
> +				argp_usage(state);
> +			}
> +		} else if (parse_var_presets(expr, &env.presets, &presets_cap, &env.npresets)) {
> +			fprintf(stderr, "Could not parse global variables preset: %s\n", arg);
> +			argp_usage(state);
> +		}
> +		free(expr);
> +		break;
> +	}
>  	default:
>  		return ARGP_ERR_UNKNOWN;
>  	}
> @@ -1292,6 +1325,273 @@ 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 *eq_ptr = strchr(expr, '=');
> +	char *name_ptr = expr;
> +	char *name_end = eq_ptr - 1;
> +	char *val_ptr = eq_ptr + 1;
> +	long long value;
> +
> +	if (!eq_ptr) {
> +		fprintf(stderr, "No assignment in expression\n");
> +		return -EINVAL;
> +	}
> +
> +	while (isspace(*name_ptr))
> +		++name_ptr;
> +	while (isspace(*name_end))
> +		--name_end;

I think this loop has to be capped by string start check,
otherwise for -G ' = 10' it might read some uninitialized memory.

> +	while (isspace(*val_ptr))
> +		++val_ptr;
> +
> +	if (name_ptr > name_end) {
> +		fprintf(stderr, "Empty variable name in expression %s\n", expr);
> +		return -EINVAL;
> +	}
> +
> +	if (*size >= *capacity) {
> +		*capacity = max(*capacity * 2, 1);
> +		*presets = realloc(*presets, *capacity * sizeof(**presets));

Nit: if realloc() fails it returns NULL,
     so the pointer to older *presets would be lost and never freed
     (but we exit the program in case of an error, so not really an issue).
     Also, check for NULL and return -ENOMEM?

> +	}
> +
> +	if (isalpha(*val_ptr)) {
> +		char *value_end = val_ptr + strlen(val_ptr) - 1;
> +
> +		while (isspace(*value_end))
> +			--value_end;
> +		*(value_end + 1) = '\0';
> +
> +		(*presets)[*size].svalue = strdup(val_ptr);

Silly question, why strdup here and for .name?
Keeping pointers to argv should be fine as far as I know.

> +		(*presets)[*size].type = NAME;
> +	} else if (*val_ptr == '-' || isdigit(*val_ptr)) {
> +		errno = 0;
> +		value = strtoll(val_ptr, NULL, 0);
> +		if (errno == ERANGE) {
> +			errno = 0;
> +			value = strtoull(val_ptr, NULL, 0);
> +		}
> +		(*presets)[*size].ivalue = value;
> +		(*presets)[*size].type = INTEGRAL;
> +		if (errno) {
> +			fprintf(stderr, "Could not parse integer value %s\n", val_ptr);
> +			return -EINVAL;
> +		}
> +	} else {
> +		fprintf(stderr, "Could not parse value %s\n", val_ptr);
> +		return -EINVAL;
> +	}
> +	*(name_end + 1) = '\0';
> +	(*presets)[*size].name = strdup(name_ptr);
> +	(*size)++;
> +	return 0;
> +}
> +
> +static int parse_var_presets_from_file(const char *filename, struct var_preset **presets,
> +				       int *capacity, int *size)

Thank you for adding this!

> +{
> +	FILE *f;
> +	char line[256];
> +	int err = 0;
> +
> +	f = fopen(filename, "rt");
> +	if (!f) {
> +		fprintf(stderr, "Could not open file %s\n", filename);
> +		return -EINVAL;
> +	}
> +
> +	while (fgets(line, sizeof(line), f)) {
> +		int err = parse_var_presets(line, presets, capacity, size);
> +
> +		if (err)
> +			goto cleanup;
> +	}
> +
> +cleanup:

Nit: I'd check for ferror(f) and write something to stderr here.

> +	fclose(f);
> +	return err;
> +}
> +
> +static bool is_signed_type(const struct btf_type *t)
> +{
> +	if (btf_is_int(t))
> +		return btf_int_encoding(t) & BTF_INT_SIGNED;
> +	if (btf_is_enum(t))
> +		return btf_kflag(t);
> +	return true;
> +}

[...]

> +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;
> +	bool *set_var;
> +	int i, j, k, n, cnt, err = 0;
> +
> +	if (npresets == 0)
> +		return 0;
> +
> +	btf = bpf_object__btf(obj);
> +	if (!btf)
> +		return -EINVAL;
> +
> +	set_var = calloc(npresets, sizeof(bool));
> +	for (i = 0; i < npresets; ++i)
> +		set_var[i] = false;

As Andrii writes in a sibling thread, I'd keep this flag in the
'struct var_preset'.

> +
> +	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;
> +
> +				if (set_var[k]) {
> +					fprintf(stderr, "Variable %s is set more than once",
> +						var_name);
> +				}
> +
> +				err = set_global_var(obj, btf, var_type, map, sinfo, presets + k);
> +				if (err)
> +					goto out;
> +
> +				set_var[k] = true;
> +				break;
> +			}
> +		}
> +	}
> +	for (i = 0; i < npresets; ++i) {
> +		if (!set_var[i]) {
> +			fprintf(stderr, "Global variable preset %s has not been applied\n",
> +				presets[i].name);
> +		}
> +	}
> +out:
> +	free(set_var);
> +	return err;
> +}
> +

[...]