site_archiver@lists.apple.com Delivered-To: darwin-dev@lists.apple.com Bob, First thanks for the reply. I am not really sure that "backwards" is the correct term. In an application (or dylib) the loader commands are included in the __TEXT segment, and then padded to have some space for some post link operations to update various tables (like two-level namespaces etc). When you look at the "sections" with in the __TEXT segment, it looks like there is a hole at the beginning of the __TEXT segment, but that space is really used for the loader commands. (It is possible I am not understanding why you think there are backwards so if my assumptions are incorrect, please clearify and I will try to explain). In my test hello world type program the last section went all the way to the last byte of the segment. From that I assumed that the __TEXT segment was for some reason layed out from end to start. The thing that made it somewhat confusing is that there is space between the end of the loader commands and the start of the __text section. I looked at a different executable and the last section didn't end at the last byte of the segment, so obviously my original assumption was wrong and the space between the loader commands and the __TEXT segment is as you say padding. Can you (or someone else) explain some more about what that space is used for? In the few executables I've looked at they were always zero filled. I am not completely sure what you mean by "__text ptrs", my understanding is that the loader can run relocations on the __TEXT segment, but really causes problems in that it forces the __TEXT segment to become write able and prevents swapping from the original image (I made that mistake 6 or so years ago and Kevin Enderby correctly slapped my hand). It is for this reason that the literal pointers end up in the __DATA segment. By ptrs I meant the offsets to the __DATA segment, sorry for the bad terminology. My intent for all this is to pop in some code into executables and frameworks/bundles that runs on load (or very soon afterwards). It seems to me like the way to do this would be either write my own dyld (which seems very hard) or add/modify the __mod_init_func section and pop in the code (after setting any offsets based on the symbol tables) in some blank space in a segment (which seems less hard and I figured __TEXT would be ideal). At 5:58 PM -0500 9/15/04, Paul Haddad wrote: On Wed, 15 Sep 2004 13:58:39 -0700, Bob Campbell <bobc@metrowerks.com> wrote: The only references to the padding is in the linker man page (man ld) and in the linker sources. It is partly for the case where the system libraries change, it allows a process to fix up paths in existing binaries (even those which are non-pick and can't be moved in memory). See -headerpad <value> and -headerpad_max_install_names. I have never really thought about how to do that, and I am not sure it is a good idea. -- Message Classification [x] General Business Information ___________________________________________________________________ Bob Campbell bobc@metrowerks.com 408.991.7490 _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.appl... This email sent to site_archiver@lists.apple.com