[ksh93-integration-discuss] Re: [ast-users] const vs. readonly data

[Glenn Fowler]

On Fri, 20 Apr 2007 18:40:26 -0400 Sam C. Nicholson !! wrote:
> Glenn Fowler wrote:
> > I've been at this so long you think I should know better
> >
> > I've been under the apparently mistaken assumption that
> > if I dilligently pepper struct definitions and subsequent
> > declarations and initializations with "const" that the compiler
> > will attempt to place that data in readonly text
> >
> > I've done this with the libast tables in conftab.c lc.c
> > but nm and size show the data going to the .data section

I did some more tests and the difference finally popped out

	struct Foo_s
	{
		const char*	bar;
	};
	const struct Foo_s foo;

with PIC enabled (I had been examining shared lib/dll code)
the struct is relegated to .data because foo.bar needs runtime relocation
with noPIC most compilers by default will put foo in .rodata or its equivalent
I knew this and forgot it (probably 10x already)

one alternative is to

		const char	bar[SOME_MAX_SIZE];

or to set up a screwy string table accessed by const indices,
possibly generated by an offline preprocessor

for now the code will stand as is until it becomes a performance issue

-- Glenn Fowler -- AT&T Research, Florham Park NJ --