Re: [PATCH v3 bpf-next 09/11] bpftool: Add ability to dump LOC_PARAM, LOC_PROTO and LOCSEC

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2026-09-16 at 08:41 +0100, Alan Maguire wrote:

...

> +static void btf_loc_param_str(const struct btf_type *t, char *str, size_t sz)
> +{
> +	const struct btf_loc_param *p;
> +	__u32 i = 0, vlen;
> +	__u64 value;
> +	bool negative = false;
> +	char regs[32] = {};
> +	char num[32] = {};
> +	const char *op = "";
> +
> +	if (!t || !btf_is_loc_param(t)) {
> +		snprintf(str, sz, "<invalid>");
> +		return;
> +	}
> +
> +	p = btf_loc_param(t);
> +	vlen = btf_vlen(t);
> +
> +	if (p->flags & BTF_LOC_PARAM_REG) {
> +		__u32 nregs = (p->flags == BTF_LOC_PARAM_REG) ? vlen : 1;
> +
> +		if (nregs > vlen) {
> +			snprintf(str, sz, "?");
> +			return;
> +		}
> +
> +		switch (nregs) {
> +		case 2:
> +			snprintf(regs, sizeof(regs), "r%u, r%u",
> +				 p->values[0], p->values[1]);

I agree with Jiri regarding the register names. It's not a huge table,
e.g. [1], 20 lines for x86 ~> 100-200 lines that would not really
change to handle all architectures that have BPF jits.
And it would be very convenient for those using the tool.

Also, it appears that simply enumerating all possible flag
combinations in a switch would make this function easier to audit for
not-handled expressions (like ADDR), or plainly reporting that the
flags are unknown for this version of the tool.

[1] https://github.com/eddyz87/inline-address-printer/blob/master/main.c#L107

> +			break;
> +		case 1:
> +			snprintf(regs, sizeof(regs), "r%u", p->values[0]);
> +			break;
> +		default:
> +			snprintf(regs, sizeof(regs), "?");
> +			break;
> +		}
> +		i += nregs;
> +	}
> +	if (p->flags & (BTF_LOC_PARAM_CONST|BTF_LOC_PARAM_OFFSET)) {

...