Why doesn't lldb forward my environment variable anymore? - c

Question

I'm working on a patch for FFmpeg and need to debug my code. I'm loading an external library, and in order to test different library versions, I have them in different folders. To select which one I want to use, I've been using DYLD_LIBRARY_PATH=/path/to/lib/dir ./ffmpeg and that works okay. But when I try it within lldb, it crashes saying dyld: Library not loaded and Reason: image not found. This used to work pre-Xcode 7.1, but I just recently upgraded and it stopped working.
Here's my MVCE:
#include <stdio.h>
#include <stdlib.h>
int main() {
char* str = getenv("DYLD_LIBRARY_PATH");
if (str) puts(str);
else puts("(null)");
return 0;
}
Running this program as follows produces the output:
$ ./a.out
(null)
$ DYLD_LIBRARY_PATH=/tmp ./a.out
/tmp
That looks okay. But when I try to use lldb it fails:
$ DYLD_LIBRARY_PATH=/tmp lldb ./a.out
(lldb) target create "./a.out"
Current executable set to './a.out' (x86_64).
(lldb) run
Process 54255 launched: './a.out' (x86_64)
(null)
Process 54255 exited with status = 0 (0x00000000)
Trying to set the environment variable inside lldb works:
lldb ./a.out
(lldb) target create "./a.out"
Current executable set to './a.out' (x86_64).
(lldb) env DYLD_LIBRARY_PATH=/tmp
(lldb) run
Process 54331 launched: './a.out' (x86_64)
/tmp
Process 54331 exited with status = 0 (0x00000000)
lldb version (it's from Xcode 7.1):
$ lldb --version
lldb-340.4.110
Question: Is this an intended new "feature," or is this a new bug in lldb (or am I totally crazy and this never used to work)? I'm quite positive lldb used to forward the DYLD_LIBRARY_PATH environment variable, so how come it isn't anymore?
Edit: This is on OS X 10.11.1.

Answer 1

If this is on El Capitan (OS X 10.11), then it's almost certainly a side effect of System Integrity Protection. From the System Integrity Protection Guide: Runtime Protections article:
When a process is started, the kernel checks to see whether the main
executable is protected on disk or is signed with an special system
entitlement. If either is true, then a flag is set to denote that it
is protected against modification. …
… Any dynamic linker (dyld)
environment variables, such as DYLD_LIBRARY_PATH, are purged when
launching protected processes.
Everything in /usr/bin is protected in this fashion. Therefore, when you invoke /usr/bin/lldb, all DYLD_* environment variables are purged.
It should work to run lldb from within Xcode.app or the Command Line Tools, like so:
DYLD_LIBRARY_PATH=whatever /Applications/Xcode.app/Contents/Developer/usr/bin/lldb <whatever else>
I don't believe that copy of lldb is protected. /usr/bin/lldb is actually just a trampoline that executes the version in Xcode or the Command Line Tools, so you're ultimately running the same thing. But /usr/bin/lldb is protected so the DYLD_* environment variables are purged when running that.
Otherwise, you will have to set the environment variable inside lldb as shown in this thread:
(lldb) process launch --environment DYLD_LIBRARY_PATH=<mydylibpath> -- arg1 arg2 arg3
or using the short -v option:
(lldb) process launch -v DYLD_LIBRARY_PATH=<mydylibpath> -- arg1 arg2 arg3
Or, you can disable System Integrity Protection, although it serves a good purpose.

Answer 2

You can set an environment variable inside lldb once it is started.
$ lldb
(lldb) help env
Shorthand for viewing and setting environment variables. Expects 'raw' input (see 'help raw-input'.)
Syntax:
_regexp-env // Show environment
_regexp-env <name>=<value> // Set an environment variable
'env' is an abbreviation for '_regexp-env'
(lldb)
So that
lldb ./a.out
(lldb) env DYLD_LIBRARY_PATH=/path/to/lib/dir
(lldb) r
should work.
Tested with
$ lldb --version
lldb-1400.0.38.17
Apple Swift version 5.7.2 (swiftlang-5.7.2.135.5 clang-1400.0.29.51)