Re: [PATCH 09/20] libdtrace: streamline kernel symbol parsing and module lookup

[Nick Alcock <nix@esperi.org.uk>]

On 30 Oct 2026, Kris Van Hees told this:

Is it really worth replacing sscanf(), which though it's a bit clunky is
at least used by other people, with even more hand-rolled parsing code?
The hex parser isn't too bad, but this:

> +static int
> +dt_modsym_parse(const char *line, int kind, dt_kallsym_t *sym)
> +{
> +	const char *end;
> +	uint64_t value;
> +	size_t len;
> +
> +	if (dt_modsym_hex(&line, &value) != 0)
> +		return -1;
> +	sym->addr = value;
> +	sym->size = 1;
> +	if (kind == DT_MODSYM_KALLMODSYMS) {
> +		if (dt_modsym_hex(&line, &value) != 0 || value > SIZE_MAX)
> +			return -1;
> +		sym->size = value;
> +	}
> +	while (isspace((unsigned char)*line))
> +		line++;
> +	if (*line == '\0')
> +		return -1;
> +	sym->type = *line++;
> +	if (!isspace((unsigned char)*line))
> +		return -1;
> +	while (isspace((unsigned char)*line))
> +		line++;
> +	len = strcspn(line, " \t\r\n");
> +	if (len == 0 || len >= sizeof(sym->name))
> +		return -1;
> +	memcpy(sym->name, line, len);
> +	sym->name[len] = '\0';
> +	line += len;
> +	while (isspace((unsigned char)*line))
> +		line++;
> +	if (*line == '\0') {
> +		strcpy(sym->mod, "vmlinux");
> +		return 0;
> +	}
> +	if (*line++ != '[' || (end = strchr(line, ']')) == NULL)
> +		return -1;
> +	len = end - line;
> +	if (len == 0 || len >= sizeof(sym->mod))
> +		return -1;
> +	memcpy(sym->mod, line, len);
> +	sym->mod[len] = '\0';
> +	return 1;		/* Explicit module name(s). */
> +}

... strikes me as exactly the sort of thing you should never ever do as
root.

Is sscanf() really noticable in profiles? (I guess it might be: we are
calling it hundreds of thousands of times, after all...)

-- 
NULL && (void)