gcc/testsuite/gcc.dg/analyzer/errno-1.c

#include <errno.h>
#include "analyzer-decls.h"

extern void external_fn (void);

int test_reading_errno (void)
{
  return errno;
}

void test_setting_errno (int val)
{
  errno = val;
}

void test_storing_to_errno (int val)
{
  __analyzer_eval (errno == val); /* { dg-warning "UNKNOWN" } */
  errno = val;
  __analyzer_eval (errno == val); /* { dg-warning "TRUE" } */
  external_fn ();
  __analyzer_eval (errno == val); /* { dg-warning "UNKNOWN" } */  
}