Const flagged as incompatible argument

[Zoltán Kócsi]

Consider the following code segment:

void    foo( const char * const m[] );

char    *bar( void );

void    baz( void )
{
char    *m[ 2 ];

        m[ 0 ] = bar();
        m[ 1 ] = bar();

        foo( m );
}

gcc 8.2.0 (and 7.4.1 as well) with -Wall gives a warning, for Intel or
ARM target:

test.c:12:7: warning: passing argument 1 of ‘foo’ from incompatible
pointer type [-Wincompatible-pointer-types] 
foo( m );
     ^
test.c:1:6: note: expected ‘const char * const*’ but argument is of
type ‘char **’

My understanding of the C standard (and I might be mistaken) is that
with the const-s I promised the compiler that foo() won't modify either
the array or the pointed strings, nothing more.

So why is the compiler complaining just because I passed a mutable
array of mutable strings? 

Also, how is it different from this case:

void foo( const char *p );
char *bar( void );
void baz( void ) { foo( bar() ); }

which is accepted by the compiler without a warning.

The warning also goes away is m[] is defined as const char *[],
but why is the warning issued in the first place? 

Thanks,

Zoltan