Re: [RFC][patch] Allow to disassemble line.

Daniel Jacobowitz
2009-10-19T19:55:33Z

On Mon, Oct 19, 2009 at 09:37:25PM +0200, Eli Zaretskii wrote:
> It's really hard to believe that 1 or 2 or 3 extra columns can make
> such a difference. Listing the source, GDB is unable to show most of
> the lines in the call stack without wrapping them, and we live with
> that. How on Earth can disassembly do worse?

Disassembly can do worse because so much of the line is usually
unintersting. The three columns won't be a huge difference, even
though they're a noticeable percentage of the screen real estate;
mostly they prompted me to start this conversation.

I usually use a 104 column terminal. Here's a sample from GDB; the
places most likely to wrap and be hard to write are calls:

0x080ec87f <handle_inferior_event+3087>: call 0x8101d90 <gdbarch_deprecated_function_start_offset>

GDB wrote that on one line and let it hard wrap.

Or one from GNU libstdc++:

0xc6bc7 <_ZSt17rethrow_exceptionNSt15__exception_ptr13exception_ptrE+87>:
callq 0x58e20 <_Unwind_RaiseException@plt>

GDB wrapped that before the callq. I can't figure out when it does
this versus when it lets things run off the end of the line; I've seen
both today.

Neither of these are unusual functions.

> > We've got this layout here with nicely aligned columns but tons of
> > whitespace. In a halfway modern world we could do this with color.
> > Or bold the address of the current instruction.
>
> I have nothing against this, but it will have to be an option, because
> dumb terminals, non-Posix emulations of termcap, and some front ends
> will need to turn it off (and then the arrow should re-appear).

Agreed. I hope that we could do this automatically in 99% of cases,
using the termcap capabilities and isatty. We do already rely on
readline which requires tgetent.

> > Another possibility would be to factor out the name of the function.
> > Something like this:
> >
> > (top) disas
> > Dump of assembler code for function gdb_main:
> > 0x0000000000454c9e (+0): push %rbp
> > 0x0000000000454c9f (+1): mov %rsp,%rbp
> > 0x0000000000454ca2 (+4): sub $0x10,%rsp
> > 0x0000000000454ca6 (+8): mov %rdi,-0x8(%rbp)
> > => 0x0000000000454caa (+12): mov -0x8(%rbp),%rax
> > 0x0000000000454cae (+16): mov 0x10(%rax),%eax
>
> I don't like this: disassembly should look like it looks elsewhere.
> However, we could offer an optional removal of the leftmost column,
> the address, and the next one, which shows the symbol and offset from
> it. Stripping leading zeros, as you point out, will help even more,
> especially on 64-bit platforms.

I use both of those pieces of information... it's the function name
that I don't use.

Joel raised a good point about the function name in x/i though.

--
Daniel Jacobowitz
CodeSourcery