Mac OS: Leaks Sanitizer - macos

Mac OS X Sierra 10.13
I do as wrote here
https://clang.llvm.org/docs/LeakSanitizer.html
I.e. created the small application with memory leak
#include <stdlib.h>
void *p;
int main() {
p = malloc(7);
p = 0; // The memory is leaked here.
return 0;
}
Then build it and run to test how the memory leak is detected:
admins-Mac:test2 admin$ clang -fsanitize=address -g mleak.c ; ASAN_OPTIONS=detect_leaks=1 ./a.out
==556==AddressSanitizer: detect_leaks is not supported on this platform.
Abort trap: 6
admins-Mac:test2 admin$
How I can detect the leak?
I need to use it for my large application.

It seems that the Clang/LLVM shipped by Apple does not have -fsanitize=leak support. I fixed it by installing LLVM on Homebrew. A more detailed fix is on gist
$ brew install llvm#8
# Overwritten default Clang
$ echo 'export PATH="/usr/local/opt/llvm/bin:$PATH"' >> .zshrc
$ source ~/.zshrc
$ which clang
/usr/local/opt/llvm/bin/clang

Note that you can also use the Leaks Instrument which ships with Xcode to find leaks in your code without having to install anything extra. It's not very well advertised, but it's a very useful tool. From the "Product" menu, choose "Profile". This may rebuild your application, and it will then launch the Instruments.app. You'll be presented with a sheet of different profiling instruments you can use like this:
Once you choose it and press the "record" button, it will run your app and display a track showing you any leaks, like this:
A green check means no leaks in the app at that time. A red "x" means a new leak since the last check. A gray "-" means there are leaks, but no new ones since the last check. The default is to check every 10 seconds.
At the bottom is a list of the current leaks. If you click on one, you'll see a stack trace on the right showing which function allocated the leaked memory.
This is a very powerful tool that has almost no documentation! I'm not sure why Apple keeps it so hidden.

If you use CLion you can try this setting:
in Preferences | Build, Execution, Deployment | CMake -> Cmake options
use
-DCMAKE_BUILD_TYPE=ASAN -DCMAKE_CXX_COMPILER=/usr/local/opt/llvm/bin/clang++
and

Related

Codesigning modified binaries (Apple Silicon/M1)

macOS on the M1 processor seems to prevent modified binaries from running. For instance, a simple C hello world:
#import <stdio.h>
int main(void) {
printf("Hello World!\n");
}
If I compile this with Clang and run it, everything works as expected. However, if I go into a hex editor and change the 'H' => 'h' (or something else trivial), the the kernel immediately sends a SIGKILL, i.e.
➜ ~ ✗ ./a.out
[1] 943 killed ./a.out
I assume this is due to the fact that there are heavier codesigning restrictions on the M1 (https://eclecticlight.co/2020/08/22/apple-silicon-macs-will-require-signed-code/), but if I try to sign the modified binary with a self-signed cert, I get a fairly non-descript error:
➜ ~ ✗ codesign -s zbaylin a.out
a.out: the codesign_allocate helper tool cannot be found or used
I know codesign_allocate is in my PATH, and I am able to sign unmodified executables, but any binary that has been modified refuses to sign.
Is there any way to sign these binaries, or disable the signature checks temporarily? I should mention that all of this works on my 2019 MacBook Pro (x86, obviously), so I think it has something to do with the M1 in particular.
Thanks!
It's a known bug in the codesign tool. To work around it, make a copy of your modified executable, sign the copy, then replace the original executable with the signed copy and it should work.
For more details, see here.

How do I create projects on Xcode 7 using wxWidgets?

My specifications are up to date (OS X El Capitan, 10.11). Here are details on what I've tried so far.
I've followed the (Terminal) installation steps included in the wxWidgets download:
mkdir build-cocoa-debug
cd build-cocoa-debug
../configure --enable-debug
make
cd samples; make;cd ..
cd demos; make;cd ..
Then, I followed the wxWidgets wiki guide for creating Xcode projects.
Of course, there were plenty of compilation errors. After taking care of an incorrectly typed include, there were still issues. For the most part, they were undeclared identifiers and incomplete types, but my attention went to one in particular:
"No Target! You should use wx-config program for compilation flags!"
After researching, I believe I need to use wx-config to find what flags to input into the "Other Linker Flags" option in Xcode. However, I can't seem to utilize wx-config in Terminal.
I'm not sure if I'm dealing with the core issue. If I am, how do I use wx-config? And if I'm not, please steer me in the right direction.
Thank you.
*** EDIT: ***
I've used wx-config to find which flags I needed to input into "Other Linker Flags" and "Preprocessor Macros" in Xcode. This significantly reduced the amount of errors and warnings that I was facing.
Unfortunately, these new errors are esoteric to me:
Error/Warning Log
How do I remove these errors so I can run this project?
I'm finally able to compile and run wxWidgets programs using Xcode 7. I've found and followed this awesome guide (of which step 3 seems to now be irrelevant).
In case the link breaks, here is a summary of the steps that helped me:
* * * * * *
Open Terminal and install Homebrew by inputting:
ruby -e "$(curl -fsSkL raw.github.com/mxcl/homebrew/go)"
Then, input:
brew install wxmac
Open Xcode and create a Command Line Tool C++ project.
Back in Terminal, input:
wx-config --libs
Once inputted, copy everything outputted by the Terminal and place it into Other Linker Flags (found in Build Settings of your Xcode project).
At Terminal, input:
wx-config -–cxxflags
Again, copy everything outputted except this time place it into Other C++ Flags (do not erase what is currently in that section).
Then, of course don't forget to include wx/wx.h and don't forget to have at least an empty main function if you want it to run.
* * * * * *
I'm not at a place where I can create Cocoa projects/products, but that's totally fine. I simply wanted a canvas to familiarize myself with the wxWidgets library.
I hope this post will be helpful to others.
Arman,
First couple of questions:
What OS are you trying to compile?
What is your requirements for the minimal OSX version?
I presume you are trying to compile the latest Git HEAD. Please correct me if its not the case.
Now, couple of recommendations:
Try to run "../configure --help" and see at all the different options you can set.
Try to run "../configure --enable-debug --with-mac-osx-version-min=10.x --with-cocoa". This command has to be run after removing the build directory completely and pretending you are starting over.
Try to open the "minimal.xcode" project in the samples/minimnal directory, add the minimal.cpp file to it and compile. If it compiles and runs fine, then you made a mistake setting up the project of your own.
Let us know how it goes.

LLDB: Must I build it from source (XCode project) to use it from the command line?

XCode comes with LLDB, presumably there is a way to enable it as the debugger to use when debugging XCode projects.
Of course being a Linux user I have become a hardcore command-line fanatic and I have a well-established Vim and Tmux workflow. Also being a code portability freak, 100% of my scripts work on both OS X and Linux.
So is there some sort of way to "Pull out" the LLDB from deep within the bowels of XCode and run it from the command line? What are the benefits of compiling it ourselves, as directed from the instructions?
I am guessing that the usual reasons to build from source apply here as well: We can get the latest bleeding edge features and bugfixes by rebuilding it. It's just better. etc. How can I check which version of clang a particular LLDB instance uses? I did compile it using the XCode project (by following those directions), and version reports:
steven#new-host-3:~/Library/Developer/Xcode/DerivedData/lldb-bvjmzslapfdmdmabqocfcogrlbfc/Build/Products/Debug Wed 3 20:37 10137
% ./lldb
(lldb) version
lldb-300.99.0
The answer won't directly help me since I already know how to build the entire thing from source, but for everyone else out there with a Mac who is thinking about ditching GDB (and actually intends to do debugging out of a command line), maybe there's a shortcut (that I skipped)!
I guess there still is a significant difference between this bleeding edge svn-sourced manually compiled LLDB and the LLDB that Apple packages with XCode and XCode CLT.
The convention on Mac OS X with Xcode 4.6 is that you either install the CommandLineTools package (which installs things in /usr/bin etc) or you prefix commands with xcrun. xcrun lldb, xcrun clang, etc. Most users of Xcode do not use command line tools so this arrangement works well. I believe you can download the CommandLineTools package alone if you're only doing command line development from http://developer.apple.com/ (I think an Apple ID is required to get access -- I think a free account will be sufficient to get the CommandLineTools package) which means you can get the full command line tools with a single 128MB download.
The change to have the canonical home for everything be in /Applications/Xcode.app is a relatively new one and the goal that drove this change was to make the developer tools relocatable. It will install in /Applications/Xcode.app if you download it from the Mac App Store, but it doesn't need to be there. You can install multiple versions of the tools on a single system - for instance, people who have access to the Xcode 5 Developer Previews will see that it installs in a separate location so the Xcode 4.6 tools are still present on the system. The xcode-select command line program can be used to specify which set of Xcode.app tools should be invoked by xcrun clang etc.
As an aside, a useful shortcut for people more comfortable building from Terminal: if you are building lldb you can do xcodebuild -configuration Debug and it will build the Debug configuration for you, no Xcode UI required.
Maybe I took the scenic route here.
% /Applications/Xcode.app/Contents/Developer/usr/bin/lldb
(lldb) version
LLDB-179.6
(lldb)
This is probably useful enough to get work done with.
It's kind of unfortunate to see that the Xcode CLT and Xcode itself come with similar tools, it's a waste of disk space.
See the sister question here.

Getting gcc to work with Xcode

I am at a place where I don't have the installation CD or the bandwidth to do a full Xcode install (It would take well over a day) to get gcc. However I did install xcode and I notice in Developer/Xcodefiles/usr/bin/ that there is gcc. When I click on it, a terminal opens up and exits complaining no input file. Is there any way I can salvage this? man gcc says no manual entry for gcc.Thanks in advance for the help.
If you want only gcc on OS X go here: https://github.com/kennethreitz/osx-gcc-installer

How can we restore ppc/ppc64 as well as full 10.4/10.5 SDK support to Xcode 4?

Since Apple only ships SDK 10.6 with Xcode4, developing PPC applications with Xcode4 became impossible. While it is possible to develop applications with Xcode4 that can also run on 10.5 and maybe even on 10.4 systems (by selecting SDK 10.6, but deployment target 10.5 or 10.4), they will only run on Intel Macs because you need at least SDK 10.5 for building PPC applications.
Further there are some rare cases, where you really need to build against an SDK prior to 10.6 for full platform support, e.g. if certain deprecated functionality has vanished completely from the 10.6 SDK, but you'll have to use it and dynamic linking is not always the best option in those cases. Also linking against an earlier SDK sometimes will ease development as functionality you are not supposed to use, as it would cause incompatibility to earlier OS versions, won't be available and any attempt to use it anyhow immediately leads to compiler or linker errors.
Last but not least Apple has also removed GCC 4.0 support from Xcode4, which may be necessary for certain software to build correctly and Apple has never allowed to compile software with GCC 4.2 when using SDK 10.4, even though I hardly believe that this would really cause any issues, after all software built with GCC 4.2 and SDK 10.6 can also run on Mac OS 10.4 without any issues as long as the deployment target has been set correctly and no functionality that is unavailable under MacOS 10.4 has been used.
Of course you can always have a parallel installation of Xcode3 next to Xcode4, but that means you must forgo all the (great?) new features of Xcode4 and keep working with the outdated Xcode3 IDE. It would certainly be much better if you could also manage all your old projects within the same IDE as your new ones and benefit from any new features available. Not all projects can be made 10.6 or Intel only in the foreseeable future. Further I'm strictly against abolishing support for older platforms earlier than would be really necessary.
Can we restore this functionality to Xcode4?
The quick answer is: Yes, we can!
Before I get to the "how it is done" part, here are some notes about my patch/hack/fix. Right from the start the major goals have been:
Keep all modifications to an absolute minimum.
We want to keep the Xcode setups as original as possible.
By all means, try to avoid patching or modifying any files.
We want all files to stay untouched and keep their original content.
Try to avoid moving or copying files around, unless absolutely necessary.
I was able to keep all those goals. Almost everything is done by creating symlinks. Only a single existing symlink had to be replaced and we'll back it up before replacement, just in case.
If you are no expert on terminal operations, I strongly advise you to copy/paste all terminal commands from my reply to your terminal, to avoid typos. Bear in mind that even spacing, quoting and especially capitalization can be important. Copy/paste them line by line, never more than one line at once and hit return after each pasted line to execute the command. Should any operation ever prompt you for a password, this will be the password of the currently logged in administrator user (your keystrokes are not displayed while typing, this is normal, don't worry, just keep typing the password and hit return; re-try if you had a typo and get prompted again).
Prerequisite
Before we can start, make sure the following conditions are true:
You are logged in as an administrator user.
You have started Terminal.app (Applications/Utilities) and a terminal window is open.
You have a copy of the Xcode3 (e.g. 3.2.5) and Xcode4 disk image (DMG) or installer available.
If you already have either Xcode version installed, consider uninstalling it first, so you can start with a fresh/clean setup. Uninstalling Xcode will not remove your preferences, color scheme or key binding customizations. Ideally you'd start with a system that has no Xcode version (neither 3 nor 4) currently installed.
Step 1: Installing Xcode3
Important: Do not install "System Tools" or "Unix Development" package of Xcode3.
Whether you want to install "Mac OS X 10.4 SDK" and/or "Documentation" is up to you. If that is a Xcode3 with iOS SDKs, whether you install those or not is also up to you.
You are free to choose any destination folder for your installation. For this guide I have chosen "/Xcode3", but feel free to pick a different one. Just make sure to alter all terminal commands accordingly.
The order of the steps given here is usually not really important, but I strongly advise you to not swap step 1 and step 2. Xcode always installs a couple of files outside of the chosen destination folder and trust me, in the end you want the Xcode4 versions of those files on your disk. By installing Xcode3 before Xcode4, you can be sure that Xcode4 will overwrite those files if necessary. I once swapped steps 1 and 2 and in the end I had some rather strange issues that might have been related to the incorrect order (I cannot say for sure, but after re-installing in the correct order the issues were gone).
Step 2: Installing Xcode4
Chose any packets you like. Installing "System Tools" is advisable, but not strictly necessary (though most people will sooner or later miss that functionality).
Again, feel free to pick any target folder you like. For this guide I chose the normal target folder "/Developer", if you take a different one, alter all terminal commands accordingly.
Step 3: Restoring 10.4/10.5 SDK Support
Switch to your terminal window and run the following commands:
cd /Developer/SDKs
sudo ln -s /Xcode3/SDKs/MacOSX10.4u.sdk .
sudo ln -s /Xcode3/SDKs/MacOSX10.5.sdk .
Of course only run the command for 10.4u if you also installed SDK 10.4 in step 1.
This is enough to bring the SDKs 10.5 (and possibly 10.4) back to the selection list in Xcode4. Give it a try if you like. Fire up Xcode4, open a project, try changing the selected SDK. That was easy, huh? Be sure to close Xcode4 again (the application, not just the window) before proceeding with the next step.
Step 4: Restoring GCC 4.0 Support
If you have not installed MacOS 10.4 SDK or if you don't plan to ever use it, you can safely skip this step and proceed with step 5.
To use SDK 10.4, you'll have to use GCC 4.0, GCC 4.2 won't work. Apple claims that GCC 4.2 is not compatible with SDK 10.4, well, if you ask me, this is a hoax. I have already overwritten this limitations more than once and there was never the tiniest issue because of it. It would be easy to modify SDK 10.4 so that Xcode will allow you to use GCC 4.2 for it, but my goal was to avoid all file modifications, so we just add GCC 4.0 support back to Xcode, which is also a good thing, because some projects really depend on GCC 4.0 (e.g. there are some bugs in GCC 4.2 that prevent valid inline assembly code to compile without errors, while the same code compiles flawlessly on GCC 4.0 and GCC 4.4).
Back to terminal:
cd /Developer/usr/bin
sudo ln -s /Xcode3/usr/bin/*4.0* .
cd /Developer/usr/libexec/gcc/powerpc-apple-darwin10
sudo ln -s /Xcode3/usr/libexec/gcc/powerpc-apple-darwin10/4.0.1 .
Right now we have restored full GCC 4.0 support except for the fact that GCC 4.0 is still not selectable in Xcode4. That is because Xcode4 has no GCC 4.0 compiler plug-in any longer. Fortunately the Xcode3 plug-in also works in Xcode4, only the position has radically changed. Apple now hides those plug-ins deep within a bundle and only plug-ins there seem to work, placing them to their old position seems to have no effect.
cd /Developer/Library/Xcode/PrivatePlugIns
cd Xcode3Core.ideplugin/Contents/SharedSupport/Developer/Library/Xcode/Plug-ins
sudo ln -s "/Xcode3/Library/Xcode/Plug-ins/GCC 4.0.xcplugin" .
Now fire up Xcode4 again, open a project and try selecting the compiler. You should have GCC 4.0 back on the list. Now you can actually already select SDK 10.4 or 10.5, GCC 4.0 and you should have no issue to build a PPC binary. Just select "Other..." for the "Architecture" build setting and manually enter "ppc", then alter "Valid Architectures" to also include "ppc". We are almost done, except that trying to build a PPC binary using GCC 4.2 and SDK 10.5 will still fail.
Step 5: Restoring PPC Support for GCC 4.2
Since Apple is only supporting Intel platforms in Xcode4, not all GCC 4.2 tools have been built with PPC support. There is one important tool that has no PPC support, the tool is named "as" and it is the GNU Assembler. To compile ppc/ppc64 binaries with GCC 4.2 we need to use an "as" version with ppc/ppc64 support. This is the one and only file (actually it also a symlink) we have to first move aside (making a backup copy) before we can replace it by a symlink:
cd /Developer/usr/libexec/gcc/powerpc-apple-darwin10/4.2.1
sudo mv as as.bak
sudo ln -s /Xcode3/usr/bin/as .
Step 6: There is No Step 6
That's all folks. Considering how easy that was, you can imagine that Apple has certainly not dropped SDK 10.4/10.5 or ppc/ppc64 or GCC 4.0 support because this was a necessity, they dropped all that because they wanted to drop it.
I hope this setup works as well for you as it does for me. I have been able to compile all my old projects in Xcode4 without any major changes, except for having to alter a search path here and there.
PS:
It may look strange that I answer my own question here, but since I have found out how to solve this problem all by myself, I'd like to share my knowledge with the community, because I believe this is really valuable input to all MacOS developers out there. This question has been asked so many times in so many places and so far I have never seen anyone coming up with a similar fix. Share the wealth, spread the knowledge and so on, you know what I mean.
If You Still Have Issues/Questions:
If you have additional questions regarding this topic or if you still have problems to build your old projects correctly, please do what Stack Overflow has been designed for: Click on "Ask Question" in the upper right corner of this page and create a new question. That way the whole community can help you solving those issues, since the issues may not directly (maybe not even indirectly) be related to this hack.
I would recommend you mention the fact that you did apply this hack at the very beginning of your question. Maybe you even want to directly link to this question, so that people, who never heard of this hack, can easily look it up. Otherwise most people will get rather confused when you mention SDK 10.4/10.5, PPC or GCC 4.0 in combination with Xcode4, which officially supports neither of these. You might get rather stupid comments instead of decent replies if you forget to mention this hack.
Please refrain from posting your questions or issues here either as replies or as comments. Posting them as replies makes no sense because they are no replies and there is no way how people can reply back to you, other then using comments, and comments may not offer enough room for a decent reply to your question or a decent solution to your problem. And posting them as comments means you are limited to very little room and tracking reply comments will be hard as comments have no tree-like hierarchy (further they will still offer to little room for decent replies/solutions). Thank you.
Of course other kind of comments as well as better replies to the original question are always welcome ;-)
Another easy way with only Xcode4, Xcode3 is no longer needed.
$ sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/libexec/gcc/darwin/ppc /Developer/usr/libexec/gcc/darwin
$ sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/libexec/gcc/darwin/ppc /usr/libexec/gcc/darwin
EDITS:
For Xcode 4.1,
sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/libexec/gcc/darwin/ppc /Developer/usr/libexec/gcc/darwin
sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/libexec/gcc/darwin/ppc /usr/libexec/gcc/darwin
sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/powerpc-apple-darwin10-cpp-4.2.1 /usr/bin/powerpc-apple-darwin11-cpp-4.2.1
sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/powerpc-apple-darwin10-gcc-4.2.1 /usr/bin/powerpc-apple-darwin11-gcc-4.2.1
sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/powerpc-apple-darwin10-g++-4.2.1 /usr/bin/powerpc-apple-darwin11-g++-4.2.1
sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/powerpc-apple-darwin10-cpp-4.2.1 /Developer/usr/bin/powerpc-apple-darwin11-cpp-4.2.1
sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/powerpc-apple-darwin10-gcc-4.2.1 /Developer/usr/bin/powerpc-apple-darwin11-gcc-4.2.1
sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/powerpc-apple-darwin10-g++-4.2.1 /Developer/usr/bin/powerpc-apple-darwin11-g++-4.2.1
sudo ln -s /Developer/Platforms/iPhoneOS.platform/Developer/usr/lib/gcc/powerpc-apple-darwin10 /Developer/SDKs/MacOSX10.6.sdk/usr/lib/gcc
You can use gcc-4.2 only for PowerPC. And “-isysroot /Developer/SDKs/MacOSX10.6.sdk” option is required, because 10.7 SDK doesn't support PowerPC any more.
I've gathered together all the information from this page, Mac OS X Hints, splhack.org, and the other sources cited here, and put together a set of BASH scripts which automate the process of restoring PPC and GCC 4.0 support using either an XCode 3 installation or just XCode 4's own iPhone platform files.
As always, use with caution! and please contribute any fixes or improvements. These scripts have only been tested on my own system as of this posting.
You can download them from GitHub:
https://github.com/thinkyhead/Legacy-XCode-Scripts
If you want gcc to work from the command line as well, (as well as the above) you'll also need to:
cd /usr/libexec/gcc/powerpc-apple-darwin10/4.2.1
sudo mv as as.bak
sudo ln -s /Xcode3/usr/bin/as .
This still works with Xcode 4.3.2 from the AppStore - the version where everything is self-contained in an App bundle. As in the original hint, install Xcode 3.2.6 first* and then download Xcode 4 from the AppStore.
Then do the following symlink magic:
cd /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/
ln -s /Developer/Xcode3.2.6/SDKs/MacOSX10.5.sdk .
cd /Applications/Xcode.app/Contents/Developer/usr/llvm-gcc-4.2/bin/
ln -s /Developer/Xcode3.2.5/usr/llvm-gcc-4.2/bin/powerpc-apple-darwin10-llvm-g* .
mv powerpc-apple-darwin10-llvm-gcc-4.2 powerpc-apple-darwin11-llvm-gcc-4.2
mv powerpc-apple-darwin10-llvm-g++-4.2 powerpc-apple-darwin11-llvm-g++-4.2
The last two lines rename darwin10 to darwin11 in the symlink - I'm guessing future versions of OS X will require this to be updated as appropriate.
To install Xcode 3.2.x on Lion, mount the Xcode disk image, open Terminal, enter the commands (using bash, or the equivalent commands if you've changed your default shell):
export COMMAND_LINE_INSTALL=1
open "/Volumes/Xcode and iOS SDK/Xcode and iOS SDK.mpkg"
You'll also need to set the clock back to a date prior to 31st March 2012 otherwise security certificates will fail validation during installation. You can safely change the date back again after installation obviously!
Frédéric Devernay has a GitHub project called xcodelegacy which works fantastic for me on Xcode 5.1.1, and needs very little work to get it going, just some downloading.
Using his project, I've managed to create universal binaries containing both ppc and i386 architectures compiled with the 10.4 SDK using GCC 4.0, all from within Xcode 5.1.1 running on Yosemite.
I've verified myself that the universal binaries created work fine on 10.5 Leopard and on Yosemite itself.
Home page here: http://devernay.free.fr/hacks/xcodelegacy
Git hub project here: https://github.com/devernay/xcodelegacy
In case someone need to restore old SDKs and PPC compiler in Xcode 4.3 and 4.5, this is a script I came up with. Note you need to set the path to the Xcode app bundle and path to Xcode 3.2.6 install at the beginning of the script.
#!/bin/bash
XCODE="/Applications/Xcode45-DP1.app"
XCODE3="/Xcode3"
# restore SDKs
cd "$XCODE/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs"
sudo ln -s "$XCODE3/SDKs/MacOSX10.4u.sdk" .
sudo ln -s "$XCODE3/SDKs/MacOSX10.5.sdk" .
sudo ln -s "$XCODE3/SDKs/MacOSX10.6.sdk" .
# restore gcc 4.0
cd "$XCODE/Contents/Developer/usr/bin"
sudo ln -s "$XCODE3/usr/bin/"*4.0* .
sudo ln -s "powerpc-apple-darwin10-g++-4.0.1" "powerpc-apple-darwin11-g++-4.0.1"
sudo ln -s "powerpc-apple-darwin10-gcc-4.0.1" "powerpc-apple-darwin11-gcc-4.0.1"
# restore Xcode option
cd "$XCODE/Contents/PlugIns/Xcode3Core.ideplugin/Contents/SharedSupport/Developer/Library/Xcode/Plug-ins"
sudo ln -s "$XCODE3/Library/Xcode/Plug-ins/GCC 4.0.xcplugin" .
You don't need to symlink 10.6 SDK if you are using Xcode 4.3 since it comes with one.
Also the script does not restore gcc 4.2 since there are a lot of filename conflicts doing that. My goal is to restore PPC compiler and 4.0 is good enough for me.
It would be useful to have a package to just install these files into an XCode 4 implementation. (or a tarball).
FYI: 3.2.6 of Xcode3 does not include an as with ppc architecture. But I had a backup of Leopard on my computer. So I copied that one, seems to work. (Use /usr/libexec/gcc/darwin/ppc/as ).
Considering that both gcc and as are open source the only stuff that may not be redistributable is the xcode plugin and the 10.4 SDK right?

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