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Re: checking command to parse /usr/bin/nm -B output from gcc object... f

From: Martin Liška
Subject: Re: checking command to parse /usr/bin/nm -B output from gcc object... failed
Date: Wed, 8 Jan 2020 10:18:23 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1

On 1/7/20 10:07 PM, Bob Friesenhahn wrote:
On Tue, 7 Jan 2020, Nick Bowler wrote:

On 1/7/20, Martin Liška <address@hidden> wrote:
nm -B detection fails to be detected with -flto and -fno-common CFLAGS:

I don't know what vintage this documentation is (the copyright says it is from 2020 so it 
seems to be the latest), but the page at says this about 

Yes, this one is for current master and we always document option that is _NOT_ 
a default.
That's why you'll see documented -fno-common in GCC 9.2.0 manual:


"The default is -fno-common, which specifies..."

GCC 9.2 documentation says that the default is target dependent, which suggests 
that some targets use no-common by default.

I'm not 100% sure which libtool features will be affected by this
configuration failure.  It doesn't fatally stop the configure script.
Probably dlpreopen won't work at all?

Are there many users of dlpreopen()?

It's also unfortunate that since there is no way to directly reference
symbol values in standard C, a common way to do so is with dummy array
or function declarations, and lo and behold LTO apparently breaks this

LTO often causes strange issues.  It needs to be used with care.

Thus far I have seen LTO reduce the output executable size (sometimes substantially if 
there is a lot of "dead" code) but I have not seen a speed benefit to properly 
written code.


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