The sentinel attribute is described in the GNU* documentation here: http://gcc.gnu.org/onlinedocs/gcc-4.4.1/gcc/Function-Attributes.html#Function-Attributes 

It says:

A valid NULL in this context is defined as zero with any pointer type. If your system defines the NULL macro with an integer type then you need to add an explicit cast.

The GNU compiler will give a diagnostic too also if "-Wformat" is specified.

Example:

#define NULL 0

//#define NULL ((void*)0)  // this fixes the problem

int execl(const char *path, const char *arg, ...) __attribute__ ((sentinel));

int main() {
   execl("","",NULL); // warning issued here
   return 0;
}

$ icc -c diag1881.c
diag1881.c(9): warning #1881: argument must be a constant null pointer value
     execl("","",NULL); // warning issued here
                 ^

Resolution status:
Use a header file that defines NULL as a pointer type (such as stddef.h) or declare NULL correctly like:

#define NULL ((void*)0)  // this fixes the problem

Cause:

This warning is issued by the driver when you have two conflicting options on the same command line. The last one on the command line "wins".Remember that command line options can exist in makefiles and config files (i.e. icc.cfg, icpc.cfg, icl.cfg or ifort.cfg).

Example:

> icc -O3 -O2 -c foo.c
icc: command line warning #10120: overriding '-O3' with '-O2'

Resolution Status:

Look at your command line and remove the redundant flag.

The Intel(R) C++ compiler for Windows needs to know which version of the Microsoft* compiler (i.e. Microsoft Visual C++ 2003*, 2005*, 2008* etc) you are using in order to set our Microsoft compability version to emulate.

For example, there are certain Microsoft bugs that exist in the Microsoft Visual C++ 2003 compiler but were fixed in Microsoft Visual C++ 2005 that we would only emulate if you had a Microsoft Visual C++ 2003 environment (header files and libraries).

In order to do this, the icl driver looks in your path for the version of cl.exe and sets the microsoft version when it calls our compiler based upon what it finds.

Example:

Compiling any program on Windows and not having "cl.exe" somewhere in your path.

Resolution status:

Change your path environment variables to include the directories where Microsoft Visual C++ executable "cl.exe", include header files and run time libraries. Easiest way is to run Visual C++ vcvars32.bat.

Or pass the options "/Qvc[7.1|8|9]" and "/Qlocation,link,"[cl-dir]" to the icl.exe.

Cause:

A header or source file does not have a terminator at the end of the file. This usually is followed by a syntax error in the file that includes the header file but can occur by itself if the terminator appears in the next file.

Example:

// diag2215.h

class C {
} // Warn on the suspect end-of-file condition here.

// diag2215.cpp
#include "diag2215.h"

Ctype;  // semicolon (terminator) is actually in the source file

int main() {
   return 0;
}

$ icpc -c diag2215.cpp
diag2215.h(4): warning #2215: definition at end of file not followed by a semicolon or a declarator
  } // no semicolon in this file
  ^

Resolution state:

Either move the terminator to the file with the last token of the type definition or suppress the warning with -wd2215 (Linux*) or -Qwd2215 (Windows*).

In standard C++98/C++03, template type arguments must have linkage, and therefore cannot be based on local or unnamed classes/enums.

So an example of where this diagnostic would be emitted is below.
g++ emits a similar diagnostic on the code below as well.

Example : 

template <class T> struct FOO {};

typedef struct { } *unnamed;

void bar() {
  FOO<unnamed> f2;
}

int main() {
  bar();
  return 0;
}

$ icc -c -V diag553.cpp
Intel(R) C Intel(R) 64 Compiler Professional for applications running on Intel(R) 64, Version 11.0    Build 20090318 Package ID: l_cproc_p_11.0.083
Copyright (C) 1985-2009 Intel Corporation.  All rights reserved.

diag553.cpp(6): error: a template argument may not reference an unnamed type
    FOO<unnamed> f2;
        ^

Resolution Status : 

We have an open bug report to allow this behaviour for Microsoft* compatibility in the Intel(R) C++ compiler for Windows.
To fix the code you should supply a name for the unnamed structure or enum.