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gcc10 compiling/linking problems
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Anon-E-moose
Watchman
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Joined: 23 May 2008
Posts: 6095
Location: Dallas area

PostPosted: Thu May 14, 2020 12:30 pm    Post subject: gcc10 compiling/linking problems Reply with quote

There seem to be several programs that won't compile without errors with the gcc-10 compiler, and the key is complaining during the linking phase about multiple definitions. These are mostly caused by default behavior of the compile changing, specifically the "common" flag.

From the release notes
Code:
GCC now defaults to -fno-common. As a result, global variable accesses are more efficient on various targets. In C, global variables with multiple tentative definitions now result in linker errors. With -fcommon such definitions are silently merged during linking.


What this means is that if you have multiple definitions in your code, and the common flag is set, you'll get a linking error.

Two ways to get things to compile.
1. add the common flag to your CFLAGS, the makes the behavior similar to pre-gcc10 compilers OR use an "env" override of "common" per package.
2. fix the code to get rid of multiple definitions.

Note: There are other problems with some packages (who thought that the gcc version would be over a single digit :roll: ) that need a code change.

Edit to add: changed no-common to common, *doh*
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Last edited by Anon-E-moose on Thu May 28, 2020 10:40 am; edited 2 times in total
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thumper
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Joined: 06 Dec 2002
Posts: 550
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PostPosted: Thu May 28, 2020 1:55 am    Post subject: Reply with quote

Don't you mean
Code:
-fcommon
makes the behavior similar to pre-gcc10 compilers.
And
Code:
-fno-common
gives linker errors for unfixed code, which is now the default.

???
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Anon-E-moose
Watchman
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Joined: 23 May 2008
Posts: 6095
Location: Dallas area

PostPosted: Thu May 28, 2020 10:38 am    Post subject: Reply with quote

Indeed, I wrote it backwards. :roll:
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Chiitoo
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Joined: 28 Feb 2010
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PostPosted: Thu May 28, 2020 10:47 am    Post subject: ><)))°€ Reply with quote

See also: wiki.gentoo.org - Gcc 10 porting notes/fno common
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