Re: [Gcl-devel] mac os x port questions

[Aurelien Chanudet]

Thanks for this clarification !

For your information, the "link edit segment" contains link edit 
information (symbol table, string table and so forth). In ELF parlance, 
this would simply be part of the data segment, so nothing worth your 
attention here. For the sake of simplification, let's not talk any 
longer of this link edit segment and do as if we simply had two 
segments (text & data) instead of three. So, let's say that my memory 
layout is the following :

- the text segment ranges from 0x00001000 to 0x0010e000
- the data segment ranges from 0x0010e000 to 0x0077e000

What you have to know is that I'm emulating sbrk, because sbrk simply 
does not work for Mac OS X. What I'm calling a hand crafted heap is 
simply a huge block of memory that gets allocated the first time sbrk() 
is called. All memory allocation in the form of calls to sbrk() takes 
place from this huge block of memory I allocated. I'm relatively free 
as to the size of this block. However, I'm not so free as to its start 
address. More particularly, I cannot make this block contiguous to the 
end of the data segment above (0x0077e000). This is because the OS 
allocates blocks on its own before I'm given a chance to allocate my 
very first one which serves as a heap. For this reason, the lowest 
memory address I can start playing with is 0x209f6000, which I reported 
yesterday as being the start of my hand crafted heap. The room between 
0x0077e000 and 0x209f6000 is managed by the OS.

> Your heap should range from DBEGIN to DBEGIN + MAXPAGE*PAGESIZE.
> Usually the first sbrk returns an address somewhat above DBEGIN,
> wasting the first few pages of this range, but this is not critical.
> But the 'hand crafted heap' of your report begins beyond the end of
> this range (!)  --- 0x2010e000 should be the end.

Ok, I've adjusted the value of DBEGIN to be the start of my heap and 
set its size to be MAXPAGE*PAGESIZE. The first sbrk(0) will return 
DBEGIN, without wasting the first few pages. See gdb session below. Any 
suggestion ? Given that I have some freedom as to how my heap can be 
organized, what's the best layout ?

I don't know what a propolice gcc is.

Thanks,
Aurelien

--

Starting program: /src/src/gcl-2.7.0/unixport/raw_pre_gcl 
/src/src/gcl-2.7.0/unixport/ -libdir /src/src/gcl-2.7.0/ < foo

Breakpoint 1, gcl_init_alloc () at alloc.c:739
739       if (initialized) return;
(gdb) n
740       initialized=1;
(gdb) n
747         malloc_list = Cnil;
(gdb) n
748         enter_mark_origin(&malloc_list);
(gdb) n
752       holepage = INIT_HOLEPAGE;
(gdb) n
758       new_holepage = HOLEPAGE;
(gdb) p holepage
$1 = 15728
(gdb) n
759       nrbpage = INIT_NRBPAGE;
(gdb) p new_holepage
$2 = 13107
(gdb) n
761       set_maxpage();
(gdb) p tm_table[t_relocatable].tm_npage
$3 = 5242
(gdb) s
set_maxpage () at alloc.c:707
707       page_multiple=getpagesize()/PAGESIZE;
(gdb) n
708       if (page_multiple==0) error("PAGESIZE must be factor of 
getpagesize()");
(gdb) n
709       if (sgc_enabled)
(gdb) n
712       int c = (int) MAXPAGE; /* I added this to ease debugging */
(gdb) n
713       int d = (int) page(core_end); /* ditto */
(gdb) p c
$4 = 131072
(gdb) p d
$5 = 0
(gdb) n
718       if (core_end)
(gdb) n
724       SET_REAL_MAXPAGE;
(gdb) n
726     }
(gdb) call my_sbrk(0) ( my_sbrk is my emulation routine for sbrk )
$6 = 0x1405000 ""
(gdb) p mach_mapstart ( this denotes the start of my heap, yesterday's 
value was 0x209f6000 )
$7 = 0x1405000 ""
(gdb) p mach_maplimit ( this denotes the end of my heap, yesterday's 
value was 0x409f6000 )
$8 = 0x1705000 <Address 0x1705000 out of bounds>
(gdb) p real_maxpage
$9 = 5893
(gdb) n
gcl_init_alloc () at alloc.c:780
780       INIT_ALLOC;
(gdb) n
783       alloc_page(-(holepage + nrbpage));
(gdb) p heap_end
$10 = 0x1405000 ""
(gdb) p core_end
$11 = 0x1405000 ""
(gdb) p holepage
$12 = 15728
(gdb) s
alloc_page (n=-20970) at alloc.c:100
100             e = heap_end;
(gdb) n
101             if (n >= 0) {
(gdb) n
144             n = -n;
(gdb) n
145             m = (core_end - heap_end)/PAGESIZE;
(gdb) n
146             if (n <= m)
(gdb) p m
$13 = 0
(gdb) n
149             IF_ALLOCATE_ERR error("Can't allocate.  Good-bye!");
(gdb) n
my_sbrk(): no more memory
MAXPAGE = 131072
page(core_end) = 0

Unrecoverable error: Can't allocate.  Good-bye!.

Program received signal SIGABRT, Aborted.
0x90042aac in kill ()
(gdb) p n
No symbol "n" in current context.
(gdb) p core_end
$14 = 0x1405000 ""
(gdb) p mach_maplimit-mach_mapstart
$15 = 3145728
(gdb) p (mach_maplimit-mach_mapstart)/0x1000
$16 = 768
(gdb) quit