Re: Question about blockframe.c:inside_main_func()

[Jason Molenda <jmolenda@apple.com>]

On Apr 29, 2004, at 8:09 AM, Andrew Cagney wrote:

> However, I think the entire function's contents are bogus.  It should 
> look like:
>
> 	if (symtab_find_function_range_by_name (main_name (), &low_pc, 
> &high_pc))
> 	  return pc in [low_pc, high_pc);
> 	else
> 	  return 0;
>
> so that the logic is pushed back into the symbol table (an obvious 
> thing for lookup_function_range_by_name to do is implement a 
> look-aside cache).

Just so I'm clear -- this is a function that doesn't exist right now, 
right?

We have at least one similar address range cache in the Apple gdb to 
keep track of some oft-referenced ObjC dispatch functions (which could 
be subsumed by a symtab_find_function_range_by_name() type function).


> (they need to be killed off anyway as PIE breaks the assumption that 
> the values are constant across function invocations).

I don't really know what PIE means - I thought it meant that the 
executable was built PIC and would be loaded at an arbitrary address on 
each run.  How could a function shift locations while the inferior is 
executing?


>> [*] We have something called "ZeroLink" where the main executable -- 
>> the symfile_objfile -- is a tiny stub that demand-loads each object 
>> file (formatted like a shared library) as functions/global variables 
>> in those .o's are referenced.  So in our case, the symfile_objfile 
>> doesn't contain main at all; hence me looking into this function and 
>> scratching my head about why it's re-searching for this function 
>> every time...
>
> you might want to look at PIE.

It's a pretty different thing, if I'm not mistaken.  PIE is about 
loading your executable at an arbitrary address, isn't it?  ZeroLink is 
about avoiding the static link editor stage in development.  You build 
your .o's (and they're built as little shared libraries), and you run 
the ZL stub program in place of your main application.  The ZL stub 
program loads at the usual 0x0 address, like a normal program.  It 
builds up a list of available functions in all the .o's and pulls them 
in on-demand.  It's entirely a development-time speed deal.  I thought 
PIE was more about security, putting the executable in different places 
so hax0rs can't hardcode where interesting functions et al are located.

Maybe I misunderstood what PIE encompasses?

Thanks,

Jason