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> What is happening? |
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gcc-10 is coming soon. It will be more disruptive than gcc-9. |
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One of the major changes is the switch from C{,XX}FLAGS=-fcommon |
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to C{,XX}FLAGS=-fno-common by default: https://gcc.gnu.org/PR85678 |
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It's a planned change and not a gcc regression. It will expose some |
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warts on old code and unblock minor optimisations accessing globals. |
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The change has already happened in gcc trunk. |
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> Is my package affected? Should I do anything? |
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You can check proactively if your packages are affected. |
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Add -fno-common to your make.conf's C{,XX}FLAGS and |
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see if things still build. |
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The typical symptom is a linker failure on multiple definitions |
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for some global variable: |
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|
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ld: a.o:(.bss+0x0): multiple definition of `a'; main.o:(.data+0x0): first defined here |
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> How to fix it? |
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https://wiki.gentoo.org/wiki/Gcc_10_porting_notes/fno_common contains |
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some examples. Ideally code will need a few 'extern' additions and maybe |
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moving variable definitions. |
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|
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Example of proposed openrc fix: |
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https://github.com/OpenRC/openrc/pull/348 |
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Adding 'append-flags -fcommon' might work as a temporary workaround. |
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> Can I help? |
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|
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Glad you asked! We will need to gather failed packages and fix them |
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upstream and downstream. Here is what you can do: |
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1. Add -fno-common to your make.conf's C{,XX}FLAGS |
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2. Build packages you maintain |
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3. Fix a bug upstream (or report a failure). |
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4. Pull a fix downstream (or file a bug and add it to the tracker). |
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> What is already known to be broken? Can I look at example fixes? |
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See https://wiki.gentoo.org/wiki/Gcc_10_porting_notes/fno_common |
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for an artificial example. |
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|
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Gentoo tracker bug of known issues: |
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https://bugs.gentoo.org/705764 |
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15 bugs so far. |
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|
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SUSE tracker bug of known issues: |
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https://bugzilla.suse.com/show_bug.cgi?id=1160244 |
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95 bugs so far. A good source of packages to check against the |
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ones you care about. |
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> What does -fcommon do? |
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Look up -fcommon in https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html |
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> I have no idea why my package broke. The error does not make sense. |
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Feel free to CC toolchain@ on a bug you observe and we'll try to sort it out. |
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-- |
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Sergei |
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