[v2] sprof: check pread size and offset for overflow

[Paul Eggert]

On 2025-10-16 12:23, DJ Delorie wrote:
> +#define PCHECK(sz,off) if ((sz) > st.st_size				\
> +			   || (off_t)(off) < 0 || (off_t)(off) > st.st_size \
> +			   ((sz)+(off_t)(off)) > st.st_size)		\

This still could have undefined behavior, as the addition in the last 
line could have signed integer overflow.

What you're trying to say here, is that SZ and OFF are both nonnegative, 
and that their sum is less than ST.st_size. I suggest saying that more 
directly, with something like this:

   void
   pcheck (long long int off, long long int sz, off_t file_size)
   {
     long long int end_off;
     if (off < 0 || sz < 0
	|| __builtin_add_overflow (off, sz, &end_off)
	|| file_size < end_off)
       error (EXIT_FAILURE, ERANGE,
	     _("read outside of file extents %lld + %lld > %lld"),
	     off, sz, (long long int) file_size);
   }

With GCC -O2 this typically generates three conditional branches; we can 
cut it down to two if that kind of efficiency is relevant here.