Question about blockframe.c:inside_main_func()

[Jason Molenda <jmolenda@apple.com>]

Hi all,

We're bringing up the currentish gdb sources here at Apple and I was 
debugging a problem with inside_main_func () [*] when I noticed that 
there seems to be a bit of extra computation that has snuck into the 
function during the changes since July.

Previously, inside_main_func() would find the "main" function in the 
"symfile_objfile", find its start and end addresses (if debug symbols 
were present I guess) and on subsequent invocations, use those cached 
addresses to determine if the addr in question is contained within the 
"main" function.

The current inside_main_func() will do

msymbol = lookup_minimal_symbol (main_name (), NULL, 
symfile_objfile);// every time

   if (msymbol != NULL             // once
       && symfile_objfile->ei.main_func_lowpc == INVALID_ENTRY_LOWPC
       && symfile_objfile->ei.main_func_highpc == INVALID_ENTRY_HIGHPC)

   if (msymbol != NULL && MSYMBOL_TYPE (msymbol) == mst_text)  // every 
time
     {
  [... lots of stuff ...]
     }

I realize this is hardly a performance critical function, but it's 
still a long shot from the version that existed before July which would 
find the start/end addresses and then do

   if (symfile_objfile->ei.main_func_lowpc == INVALID_ENTRY_LOWPC &&  // 
once
       symfile_objfile->ei.main_func_highpc == INVALID_ENTRY_HIGHPC)
   [... lookup symbol ... ]

   return (symfile_objfile->ei.main_func_lowpc <= pc
           && symfile_objfile->ei.main_func_highpc > pc);


Is there some reason why this shortcut has been dropped?  Is there a 
reason not to add a conditional to the top to detect "main"'s bounds 
being detected and short-circuit the searching we're doing every time.

Jason

[*] 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...