Re: [PATCH v4 11/28] objtool: Trace instruction state changes during function validation

[Alexandre Chartre]

On 11/14/25 22:21, Josh Poimboeuf wrote:
> On Thu, Nov 13, 2025 at 05:49:00PM +0100, Alexandre Chartre wrote:
> > +/*
> > + * Return the name of a register. Note that the same static buffer
> > + * is returned if the name is dynamically generated.
> > + */
> > +static const char *cfi_reg_name(unsigned int reg)
> > +{
> > +	static char rname_buffer[CFI_REG_NAME_MAXLEN];
> > +
> > +	switch (reg) {
> > +	case CFI_UNDEFINED:
> > +		return "<undefined>";
> > +	case CFI_CFA:
> > +		return "cfa";
> > +	case CFI_SP_INDIRECT:
> > +		return "(sp)";
> > +	case CFI_BP_INDIRECT:
> > +		return "(bp)";
> > +	}
> > +
> > +	if (snprintf(rname_buffer, CFI_REG_NAME_MAXLEN, "r%d", reg) == 1)
> > +		return NULL;
>
> An snprintf() error would either be -1 (error) or ">=
> CFI_REG_NAME_MAXLEN" (truncation).
>
> Also maybe return "(error)" or so, so the caller doesn't need to check
> the return value.

Right, I will fix that.

> > +static void trace_cfi_reg(const char *prefix, int reg, const char *fmt,
> > +			  int base_prev, int offset_prev,
> > +			  int base_next, int offset_next)
> > +{
> > +	const char *rname;
> > +
> > +	if (base_prev == base_next && offset_prev == offset_next)
> > +		return;
> > +
> > +	if (prefix)
> > +		TRACE("%s:", prefix);
> > +
> > +	rname = cfi_reg_name(reg);
> > +
> > +	if (base_next == CFI_UNDEFINED) {
> > +		TRACE("%1$s=<undef> ", rname);
> > +	} else {
> > +		TRACE(fmt, rname,
> > +		      cfi_reg_name(base_next), offset_next);
>
> Since cfi_reg_name() can reuse the same static local buffer, rname and
> cfi_reg_name(base_next) might point to the same string?

Yes, good catch. I will fix.

Thanks,

alex.