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Re: recent master core dumps building on FreeBSD i386

From: Joseph Mingrone
Subject: Re: recent master core dumps building on FreeBSD i386
Date: Thu, 18 Oct 2018 22:15:08 -0300
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (berkeley-unix)

Paul Eggert <address@hidden> writes:

> On 10/18/18 9:02 AM, Eli Zaretskii wrote:
>> Can you please repeat this experiment, and then, when it crashes, do
>> this:

>>    (gdb) source ./.gdbinit
>>    (gdb) frame 2
>>    (gdb) p/x a
>>    (gdb) xtype

>> and show us the results?

> Also, please try these GDB commands when debugging ./temacs:

> b syms_of_threads
> r -Q
> p &main_thread
> disas syms_of_threads
> p &Vmain_thread

> I'm attaching the output of these commands on Fedora 28 x86-64 compiled with 
> 'gcc -m32 -march=native -g3 -O2' (AMD Phenom II X4 910e). Evidently your 
> compiler (clang?) is not inlining make_lisp_ptr, but
> it's still useful to know what it's up to. I see that GCC optimizes away not 
> only the call to make_lisp_ptr, but also the runtime check 'TAGGEDP (a, type) 
> && XUNTAG (a, type, char) == ptr', I guess because
> GCC knows that main_thread is properly aligned so TAGGEDP must succeed here. 
> clang isn't smart enough to do this sort of optimization (at least on Fedora) 
> so if you're using clang that might partly explain
> the problem.

> Also, please investigate what the macro GCALIGNED_STRUCT expands to. You can 
> use 'gcc -E' to do that.

Is it still helpful for me to investigate what GCALIGNED_STRUCT expands to?  If 
so, could elaborate on how I can get this?

Paul Eggert <address@hidden> writes:
> main_thread is not properly aligned; its address is a multiple of 4, but it 
> should be a multiple of 8. That's the problem. Somehow GCALIGNED_STRUCT is 
> not working on your platform.

Is there anything else helpful for me to investigate or do you recommend that I 
report this problem elsewhere?

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