Re: [RFA 2/5] Darwin: Handle unrelocated dyld.

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2018-09-19 15:15, Tom Tromey wrote:
> > > > > > "Simon" == Simon Marchi <simon.marchi@polymtl.ca> writes:
>
> Simon> I would vote for only checking in the code you know is necessary 
> for
> Simon> now, otherwise it will just be more confusing in the future, 
> trying to
> Simon> figure out what is needed and what isn't.
>
> Here is a more minimal version of the patch.  This one seems to work 
> for
> me on High Sierra.  I tried running a "hello world" program -- this
> previously failed, but now works.  It's good enough that I could run
> gdb.cp/*.exp -- lots of fails but no crashes or mystery problems.
>
> Tom
>
> commit 114a1aae792443d72f1438dbc979b42a39c5b780
> Author: Xavier Roirand <roirand@adacore.com>
> Date:   Wed Aug 22 12:11:14 2018 +0200
>
>     Darwin: Handle unrelocated dyld.
>
>     On Darwin, debugging an helloworld program with GDB does
>     not work and ends with:
>
>       (gdb) set startup-with-shell off
>       (gdb) start
>       Temporary breakpoint 1 at 0x100000fb4: file /tmp/helloworld.c, 
> line 1.
>       Starting program: /private/tmp/helloworld
>       [New Thread 0x2703 of process 18906]
>       [New Thread 0x2603 of process 18906]
>
>       [1]+  Stopped                 ./gdb/gdb /tmp/helloworld
>
>     When debugging with lldb, instead of having the STOP signal, we can
>     see that a breakpoint is not set to a proper location:
>
>       Warning:
>       Cannot insert breakpoint -1.
>       Cannot access memory at address 0xf726
>
>       Command aborted.
>
>     The inserted breakpoint is the one used when GDB has to stop the 
> target
>     when a shared library is loaded or unloaded. The notifier address 
> used
>     for adding the breakpoint is wrong thus the above failure.
>     This notifier address is an offset relative to dyld base address, 
> so
>     the value calculation has to be updated to reflect this.
>
>     This was tested on High Sierra by trying to run a simple "hello 
> world"
>     program.

Works for me, thanks!  I just noted some nits.

> @@ -459,6 +457,18 @@ darwin_solib_get_all_image_info_addr_at_init
> (struct darwin_info *info)
>        else
>  	dyld_bfd.release ();
>      }
> +  return dyld_bfd;
> +}
> +
> +/* Extract dyld_all_image_addr when the process was just created, 
> assuming the
> +   current PC is at the entry of the dynamic linker.  */
> +
> +static void
> +darwin_solib_get_all_image_info_addr_at_init (struct darwin_info 
> *info)
> +{
> +  CORE_ADDR load_addr = 0;
> +  gdb_bfd_ref_ptr dyld_bfd (darwin_get_dyld_bfd ());

Use =.

> +
>    if (dyld_bfd == NULL)
>      return;
>
> @@ -528,10 +538,6 @@ darwin_solib_create_inferior_hook (int from_tty)
>        return;
>      }
>
> -  /* Add the breakpoint which is hit by dyld when the list of solib is
> -     modified.  */
> -  create_solib_event_breakpoint (target_gdbarch (), 
> info->all_image.notifier);
> -
>    if (info->all_image.count != 0)
>      {
>        /* Possible relocate the main executable (PIE).  */
> @@ -558,6 +564,49 @@ darwin_solib_create_inferior_hook (int from_tty)
>        if (vmaddr != load_addr)
>  	objfile_rebase (symfile_objfile, load_addr - vmaddr);
>      }
> +
> +  /* Set solib notifier (to reload list of shared libraries).  */
> +  CORE_ADDR notifier = info->all_image.notifier;
> +
> +  if (info->all_image.count == 0)
> +    {
> +      /* Dyld hasn't yet relocated itself, so the notifier address may
> +	 be incorrect (as it has to be relocated).  */
> +      CORE_ADDR start = bfd_get_start_address (exec_bfd);
> +      if (start == 0)
> +	notifier = 0;
> +      else
> +        {
> +          gdb_bfd_ref_ptr dyld_bfd (darwin_get_dyld_bfd ());

Here too.

Simon