I know I can get the assembler source code generated by the compiler by using:
gcc -S ...
even though that annoyingly doesn't give me an object file as part of the process.
But how can I get everything about the compiled code? I mean addresses, the bytes generated and so forth.
The instructions output by gcc -S do not tell me anything about instruction lengths or encodings, which is what I want to see.
I like objdump for this, but the most useful options are non-obvious - especially if you're using it on an object file which contains relocations, rather than a final binary.
objdump -d some_binary does a reasonable job.
objdump -d some_object.o is less useful because calls to external functions don't get disassembled helpfully:
...
00000005 <foo>:
5: 55 push %ebp
6: 89 e5 mov %esp,%ebp
8: 53 push %ebx
...
29: c7 04 24 00 00 00 00 movl $0x0,(%esp)
30: e8 fc ff ff ff call 31 <foo+0x2c>
35: 89 d8 mov %ebx,%eax
...
The call is actually to printf()... adding the -r flag helps with that; it marks relocations. objdump -dr some_object.o gives:
...
29: c7 04 24 00 00 00 00 movl $0x0,(%esp)
2c: R_386_32 .rodata.str1.1
30: e8 fc ff ff ff call 31 <foo+0x2c>
31: R_386_PC32 printf
...
Then, I find it useful to see each line annotated as <symbol+offset>. objdump has a handy option for that, but it has the annoying side effect of turning off the dump of the actual bytes - objdump --prefix-addresses -dr some_object.o gives:
...
00000005 <foo> push %ebp
00000006 <foo+0x1> mov %esp,%ebp
00000008 <foo+0x3> push %ebx
...
But it turns out that you can undo that by providing another obscure option, finally arriving at my favourite objdump incantation:
objdump --prefix-addresses --show-raw-insn -dr file.o
which gives output like this:
...
00000005 <foo> 55 push %ebp
00000006 <foo+0x1> 89 e5 mov %esp,%ebp
00000008 <foo+0x3> 53 push %ebx
...
00000029 <foo+0x24> c7 04 24 00 00 00 00 movl $0x0,(%esp)
2c: R_386_32 .rodata.str1.1
00000030 <foo+0x2b> e8 fc ff ff ff call 00000031 <foo+0x2c>
31: R_386_PC32 printf
00000035 <foo+0x30> 89 d8 mov %ebx,%eax
...
And if you've built with debugging symbols (i.e. compiled with -g), and you replace the -dr with -Srl, it will attempt to annotate the output with the corresponding source lines.
The easiest way to get a quick listing is to use the -a option to the assembler, which you can do by putting -Wa,-a on the gcc command line. You can use various modifiers to the a option to affect exactly what comes out -- see the as(1) man page.
It sounds to me like you want a disassembler. objdump is pretty much the standard (otool on Mac OS X); in concert with whatever map file information your linker gives you, the disassembly of your object file should give you everything you want.
gcc will produce an assembly language source file. You can then use as -a yourfile.S to produce a listing that includes offsets and encoded bytes for each instruction. -a also has some sub-options to control what shows up in the listing file (as --help will give a list of them along with the other available options).
nasm -f elf xx.asm -l x.lst
gcc xx.c xx.o -o xx
generates a 'list' file x.lst which is only for xx.asm
for xx.c along with xx.asm you can compile them both and then use 'gdb' - gnu debugger
