I have the problem, that for testing purposes I want to place an Objective-C message at a certain place in memory.
Now my plan is, that I link my foundation console project with -seg1addr 0x35203000 and I have another method in front of the method, that contains a lot of dummy code, that I want to shrink or expand to hit the proper address.
+ (int) bogus1:(int) x
{
x = x * x;
x = x * x;
// and hundreds more...
// x = x * x;
return( x);
}
- (id) key
{
return( _key);
}
It's not working as I hoped it would be, although the -seg1addr in itself works.
The reason being, that the first __text start address changes unpredictably.
Here is an example of a link with _more_ bogus1 code:
Load command 1
cmd LC_SEGMENT
cmdsize 396
segname __TEXT
vmaddr 0x35203000
vmsize 0x00002000
fileoff 0
filesize 8192
maxprot 0x00000007
initprot 0x00000005
nsects 5
flags 0x0
Section
sectname __text
segname __TEXT
addr 0x35204544
size 0x000009cd
offset 5444
align 2^2 (4)
reloff 0
nreloc 0
flags 0x80000400
reserved1 0
reserved2 0
and here with less bogus1 code, as you can see the __text address counterintuitively moved down! I would have expected it to stay the same really.
Load command 1
cmd LC_SEGMENT
cmdsize 396
segname __TEXT
vmaddr 0x35203000
vmsize 0x00002000
fileoff 0
filesize 8192
maxprot 0x00000007
initprot 0x00000005
nsects 5
flags 0x0
Section
sectname __text
segname __TEXT
addr 0x35204684
size 0x0000089b
offset 5764
align 2^2 (4)
reloff 0
nreloc 0
flags 0x80000400
reserved1 0
reserved2 0
Most of the space between 0x35204684 and 0x35203000 is filled with beautiful nils. So apparently the linker somehow tail aligns the code ?
I then added a method bogus2 behind the -key method, but I still can't nail the exact address. I can come close to one byte offset with nops though.
I need a clue...
Ciao
Nat!
P.S. If you think this is crazy, see this :) (http://www.mulle-kybernetik.com/weblog/2009/12/my_best_bug_ever.html), the reason I am trying this at all.
------------------------------------------------------
When vanity and rivalry disappear, all the lines go
out of your stomach and you slow down and coast
slowly to a stop in the middle. -- DLR
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