This is GDB modified for use with Darling. It enables you to debug Mach-O code loaded by dyld (via Darling's mldr).
I build GDB like this, adapt it to your preferences:
./configure --disable-werror --disable-binutils --disable-etc \
--disable-gas --disable-gold --disable-gprof --disable-ld \
--enable-gdbserver=auto --enable-64-bit-bfd --disable-install-libbfd \
--disable-install-libiberty --without-guile --disable-readline \
--with-system-readline --without-zlib --with-system-zlib \
--with-separate-debug-dir=/usr/lib/debug --without-expat \
--without-lzma --enable-nls --enable-targets=all --program-suffix=-darling \
--prefix=/usr/local/libexec/darling
It is not yet possible to run Mach-O executables directly, you must tell gdb to run them through mldr:
gdb-darling /bin/mldr
(gdb) r /some/apple/binary
Explanation: mldr is a simple Mach-O loader that loads Apple's dynamic loader (dyld) and hands control over to it.
You should be able to see valid backtraces where debug info is available:
(gdb) bt
#0 puts (s=0x7ffff7618faa "Hello world") at /home/lubos/Projects/darling/src/libc/stdio/FreeBSD/puts.c:64
#1 0x00007ffff7618f7d in main () from /home/lubos/Projects/hello
#2 0x00007ffef74e6455 in start () from /usr/local/libexec/darling/usr/lib/system/libdyld.dylib
#3 0x00007ffef74e6455 in start () from /usr/local/libexec/darling/usr/lib/system/libdyld.dylib
#4 0x0000000000000000 in ?? ()
Or examine what libraries are loaded at which addresses:
(gdb) info sharedlibrary
From To Syms Read Shared Object Library
0x00007ffff7ddaaa0 0x00007ffff7df5de0 Yes /lib64/ld-linux-x86-64.so.2
0x00007ffff7bc2a60 0x00007ffff7bcf871 Yes /lib/x86_64-linux-gnu/libpthread.so.0
0x00007ffff79b9d80 0x00007ffff79ba93e Yes /lib/x86_64-linux-gnu/libdl.so.2
0x00007ffff763a910 0x00007ffff77642c3 Yes /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7618f60 0x00007ffff7619018 Yes (*) /home/lubos/Projects/hello
0x00007ffff7ff0780 0x00007ffff7ff1210 Yes /usr/local/libexec/darling/usr/lib/libSystem.B.dylib
0x00007ffff7fec990 0x00007ffff7fed020 Yes (*) /usr/local/libexec/darling/usr/lib/system/libsystem_sandbox.dylib
0x00007ffff7fe9900 0x00007ffff7fea070 Yes /usr/local/libexec/darling/usr/lib/system/libquarantine.dylib
0x00007ffff7fe4930 0x00007ffff7fe7168 Yes (*) /usr/local/libexec/darling/usr/lib/system/libremovefile.dylib
0x00007ffff7fd5a20 0x00007ffff7fe1350 Yes (*) /usr/local/libexec/darling/usr/lib/system/libcopyfile.dylib
0x00007ffff7e1a550 0x00007ffff7e28b21 Yes /usr/local/libexec/darling/usr/lib/system/libunwind.dylib
0x00007ffff7fd26b0 0x00007ffff7fd3478 Yes (*) /usr/local/libexec/darling/usr/lib/system/libsystem_coreservices.dylib
0x00007ffef75d5f90 0x00007ffef7614070 Yes (*) /usr/local/libexec/darling/usr/lib/libcommonCrypto.dylib
0x00007ffef7587450 0x00007ffef75bb6e8 Yes /usr/local/libexec/darling/usr/lib/system/libsystem_info.dylib
0x00007ffff7e01200 0x00007ffff7e13400 Yes (*) /usr/local/libexec/darling/usr/lib/system/libsystem_notify.dylib
0x00007ffef753cf80 0x00007ffef7568a68 Yes /usr/local/libexec/darling/usr/lib/system/libdispatch.dylib
0x00007ffff7fcd2e0 0x00007ffff7fcf9f0 Yes (*) /usr/local/libexec/darling/usr/lib/system/libsystem_blocks.dylib
0x00007ffef74f2750 0x00007ffef752c6ad Yes /usr/local/libexec/darling/usr/lib/system/libsystem_malloc.dylib
0x00007ffef74ee5e0 0x00007ffef74ef098 Yes (*) /usr/local/libexec/darling/usr/lib/system/libkeymgr.dylib
0x00007ffef74e2620 0x00007ffef74e8554 Yes (*) /usr/local/libexec/darling/usr/lib/system/libdyld.dylib
0x00007ffef74c6330 0x00007ffef74d65a0 Yes /usr/local/libexec/darling/usr/lib/system/liblaunch.dylib
0x00007ffef72c3500 0x00007ffef743749c Yes /usr/local/libexec/darling/usr/lib/system/libsystem_c.dylib
0x00007ffef726fde0 0x00007ffef72aa294 Yes /usr/local/libexec/darling/usr/lib/system/libsystem_m.dylib
0x00007ffef72638d0 0x00007ffef726c7c0 Yes (*) /usr/local/libexec/darling/usr/lib/system/libmacho.dylib
0x00007ffef71d5dd0 0x00007ffef7229ce0 Yes /usr/local/libexec/darling/usr/lib/system/libsystem_kernel.dylib
0x00007ffff7dfd790 0x00007ffff7dfe01c Yes (*) /usr/local/libexec/darling/usr/lib/system/libsystem_duct.dylib
0x00007ffef71bad40 0x00007ffef71cc1f8 Yes (*) /usr/local/libexec/darling/usr/lib/system/libcompiler_rt.dylib
0x00007ffef7173970 0x00007ffef71b10d0 Yes (*) /usr/local/libexec/darling/usr/lib/libresolv.9.dylib
(*): Shared library is missing debugging information.
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