Re: [PATCH] x86/setup: replace strlcat() with snprintf() in setup_arch()

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Fri, Jun 05, 2026 at 05:42:48PM +0200, Thorsten Blum wrote:
> On Fri, Jun 05, 2026 at 07:41:11AM +0300, Andy Shevchenko wrote:
> > On Thu, Jun 04, 2026 at 03:17:53PM +0200, Thorsten Blum wrote:

...

> > >  	strscpy(boot_command_line, builtin_cmdline, COMMAND_LINE_SIZE);
> > 
> > This also has third argument fixed. Don't you want to change that?
> 
> That doesn't work because boot_command_line, at least the declaration in
> linux/init.h, doesn't have a fixed size.

Ah, okay.

> > >  #else
> > >  	if (builtin_cmdline[0]) {
> > > +		size_t len = strnlen(builtin_cmdline, COMMAND_LINE_SIZE);
> > > +
> > >  		/* append boot loader cmdline to builtin */
> > > -		strlcat(builtin_cmdline, " ", COMMAND_LINE_SIZE);
> > > -		strlcat(builtin_cmdline, boot_command_line, COMMAND_LINE_SIZE);
> > > +		snprintf(builtin_cmdline + len, COMMAND_LINE_SIZE - len, " %s",
> > > +			 boot_command_line);
> > 
> > Hmm... Wouldn't GCC complain on this? (Build with `make W=1`.)
> 
> No warnings with W=1. Why would GCC warn here?

Sometimes it complains if it can't prove the size of the string to fit the
destination. You said that there is no size for boot_command_line, I'm not
sure I understand how GCC proves that the above snprintf() won't ever truncate
the input.

> > >  		strscpy(boot_command_line, builtin_cmdline, COMMAND_LINE_SIZE);
> > 
> > And this has also third argument.
> 
> Same reason as above.

-- 
With Best Regards,
Andy Shevchenko