Date: Mon, 21 Jun 2021 11:25:29 -0400 From: Ed Maste <emaste@freebsd.org> To: Steve Kargl <sgk@troutmask.apl.washington.edu> Cc: John Baldwin <jhb@freebsd.org>, Poul-Henning Kamp <phk@phk.freebsd.dk>, "freebsd-arch@freebsd.org" <arch@freebsd.org> Subject: Re: It's time to kill statistical profiling Message-ID: <CAPyFy2AqFgya66PiyjFB2Xkbck3rMqVNEtTgEYDnNhw7P8EXpQ@mail.gmail.com> In-Reply-To: <20210620210825.GA45154@troutmask.apl.washington.edu> References: <202106180736.15I7aYmk068064@critter.freebsd.dk> <d63d21fe-c1ef-dbb9-64e2-3e23621820bc@FreeBSD.org> <CAPyFy2BV0R_uXir1dYf8nN2JEOCZCprKYbHa6E1biFFJMbmAQQ@mail.gmail.com> <20210620210825.GA45154@troutmask.apl.washington.edu>
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On Sun, 20 Jun 2021 at 17:08, Steve Kargl
<sgk@troutmask.apl.washington.edu> wrote:
>
> Are there plans to replace the _p.a with something
> that allows profiling code? If not, are you upstreaming
> patches to GCC to disable -pg? AFAIK, 'gcc10 -pg ... -lm'
> causes gcc to look for at least libc_p.a and libm_p.a.
I believe this is how GCC operates indeed, but I'm not aware of the
implementation or specific details. Clang behaves as you describe --
here is all behaviour change based on OPT_pg, from
lib/Driver/ToolChains/FreeBSD.cpp:
if (!Args.hasArg(options::OPT_shared)) {
if (Args.hasArg(options::OPT_pg))
crt1 = "gcrt1.o";
else if (IsPIE)
crt1 = "Scrt1.o";
else
crt1 = "crt1.o";
}
...
if (Args.hasArg(options::OPT_pg))
CmdArgs.push_back("-lm_p");
else
CmdArgs.push_back("-lm");
and similar for -lgcc_p, -lgcc_eh_p, -lpthread_p, -lc_p, -lc++_p, -lstdc++_p.
This support was initially introduced upstream in:
commit 66f2276aee67738d116d26494d8a78fc6528586b
Author: Roman Divacky <rdivacky@freebsd.org>
Date: Thu Feb 10 16:59:40 2011 +0000
Adjust the object files to be linked in when mcount profiling
is specified in the FreeBSD linker driver.
llvm-svn: 125285
and was implemented for OpenBSD later that year, but no other OS does
this. I'm not sure exactly what happens elsewhere - my guess is that
the runtime support exists in libc but it is built without -pg so
coverage will not include libc itself.
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