A toy program to teach myself more about the mach-o file format. Right now,
it roughly does what `dsymutil -s` does (which is a bit more than `nm`), but
worse.
Demo
----
But one can already see interesting things with this tool.
See symbols in `lssym` (like with `nm`, but with some `otool -l` thrown in):
clang -o lssym lssym.c -Wall
./lssym lssym
See what's left after stripping:
strip lssym
./lssym lssym
(Compare with the output of `nm lssym` and `dsymutil -s lssym` in both cases.
Note that `strip` adds a symbol that looks like
radr://5614542 N_STAB 3c n_sect 000 n_desc 0x0000 n_value 0x5614542
I wonder what that bug is. `nm` doesn't list it because `nm` only lists symbols,
and this is a stabs debug info entry which `nm` only shows if you pass `-a`.)
Now build with debug info:
clang -o lssym lssym.c -Wall -gdwarf-2
./lssym lssym
Note that the file now includes stabs debug info, even though we asked for
dwarf. `dsymutil lssym` complains about a temporary `.o` file. Let's break up
compile and link step:
clang -c lssym.c -Wall -gdwarf-2
clang -o lssym lssym.o
dsymutil lssym
./lssym lssym # Still contains stabs entries.
dwarfdump lssym.dSYM # But this finds dwarf info now, too.
dwarfdump lssym.o # So does this.
dwarfdump lssym # This doesn't.
If you don't want `ld` to write stabs info (since you have a dSYM, it's
pointless, and might slow down the `ld` step), link like this:
clang -o lssym lssym.o -Wl,-S
If you pass `-Wl,-s` instead, `ld` will claim that `-s` is obsolete and ignored,
but still still strip all symbols that can be stripped (after first writing them
as far as I understand -- so that probably doesn't help with linker
performance).
Related tools
-------------
* `dyldinfo` can show relocation info (`man dyldinfo` works, but dyldinfo isn't
in my path for some reason -- `xcrun dyldinfo` finds it though)
- e.g. -exports, -opcodes, ...
* `dyld_info` is apparently different from `dyldinfo`, and can print chained
relocs, dependent librarys, opcodes, ... (and it doesn't need `xcrun`)
* `dwarfdump` shows dwarf debug data
* `dsymutil` can show symbol tables (`-s`) and link dwarf debug info from .o
files into a single .dSYM file.
* `nm` shows references symbols; a subset of `dsymutil -s` output.
* `otool -l` all load commands in a mach-o file.
* `dwarfdump --file-stats lssym`
* `atos`
* `dwarfdump --lookup`
* run programs with `DYLD_PRINT_STATISTICS=1` set (see `man dyld` for more flags)
http://wiki.dwarfstd.org/index.php?title=Apple's_%22Lazy%22_DWARF_Scheme