DMD Backend: Deciding instructions to use/avoid?

[Nick Sabalausky]

"Andrew Wiley" <wiley.andrew.j at gmail.com> wrote in message 
news:mailman.762.1307693296.14074.digitalmars-d-learn at puremagic.com...
> On Thu, Jun 9, 2011 at 5:58 PM, Nick Sabalausky <a at a.a> wrote:
>
>> "Bernard Helyer" <b.helyer at gmail.com> wrote in message
>> news:isdgdc$m3a$1 at digitalmars.com...
>> > If you run the program in GDB, can you disassemble when the error is
>> > given? That may give you the instruction the kernel is assasinating 
>> > your
>> > process for.
>>
>> I can try that if anyone can help walk me through it or at least point me
>> to
>> a good beginner's tutorial for gdb. I never use commandline debuggers, 
>> and
>> I've never even touched gdb, so I don't have the slightest clue how to 
>> use
>> it.
>>
>>
>> The short version is to run `gdb yourapp` which will get you into the GDB
> shell. Then `run` to actually start the app. It will halt and return to 
> the
> shell when it hits the bad instruction, and you should type `disass` to 
> view
> the assembly code of the current function. There will be a pointer (->, I
> think) pointing to the current instruction in the listing.
> You can find GDB basics at http://www.cs.cmu.edu/~gilpin/tutorial/ 
> although
> that tutorial doesn't include `disass`. I mostly learned it by firing it 
> up
> and typing `help`  :D
>

Thanks. This is what I get:

$ gdb ./dvm-0.2.0-linux-32
GNU gdb (GDB) 7.1-ubuntu
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/nick/dev/d/tool/dvm-0.2.0-linux-32...(no 
debugging symbols found)...done.
(gdb) run
Starting program: /home/nick/dev/d/tool/dvm-0.2.0-linux-32
[Thread debugging using libthread_db enabled]

Program received signal SIGILL, Illegal instruction.
0x080bccdb in 
_D5tango4core4sync6Atomic31__T13memoryBarrierVb1Vb0Vi0Vb0Z13memoryBarrierFZv 
()
(gdb) disass
Dump of assembler code for function 
_D5tango4core4sync6Atomic31__T13memoryBarrierVb1Vb0Vi0Vb0Z13memoryBarrierFZv:
   0x080bccd8 <+0>:     push   %ebp
   0x080bccd9 <+1>:     mov    %esp,%ebp
=> 0x080bccdb <+3>:     lfence
   0x080bccde <+6>:     pop    %ebp
   0x080bccdf <+7>:     ret
End of assembler dump.
(gdb)

So apperently it's a memory fence instruction. I don't have a clue what my 
CPU supports in that area. Oh, and apperently it's inside Tango, so maybe 
I'll bring this up over there. But I have no idea if that's something that 
Tango has in common with druntime or not.