Re: compiler warnings with gcc 4.8 and -Og

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>
Subject: Re: compiler warnings with gcc 4.8 and -Og
Date: 2022-06-02 15:04:30
Message-ID: 20220602150430.5ewy3ustj3eqrcl5@alap3.anarazel.de
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Hi,

On 2022-06-02 10:33:52 -0400, Tom Lane wrote:
> Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com> writes:
> > On Thu, 2 Jun 2022, 07:10 Tom Lane, <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> I'm a little dubious about whether -Og is a case we should pay special
> >> attention to?
>
> > The "Developer FAQ" page on the wiki suggests that when you develop
> > with gcc that you use CFLAGS="-ggdb -Og -g3 -fno-omit-frame-pointer"
> > during development, so I'd hardly call -Og "any random option".
>
> I have no idea who wrote that FAQ entry, and I'd certainly not
> accept it as being project policy.

I don't know either. However:

> I'd actually say that's an excellent example of adding some random compiler
> options.

To me they mostly make sense. -g3 with -ggdb makes gcc emit enough information
about macros that the debugger can interpret them. -fno-omit-frame-pointer
makes profiling with call graphs much much smaller.

I tried to use -Og many times, but in the end mostly gave up, because it still
makes debugging harder compared to -O0.

Greetings,

Andres Freund

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