Bug 217013

Summary: 4.14.304 regression: error building with arch/x86/kernel/fpu/init.c due to missing _Alignof support in GCC < 4.7
Product: Platform Specific/Hardware Reporter: it
Component: x86-64Assignee: gregkh
Status: NEW ---    
Severity: normal CC: bp, greg, gregkh
Priority: P1    
Hardware: All   
OS: Linux   
Kernel Version: 4.14.304 Subsystem:
Regression: Yes Bisected commit-id:

Description it 2023-02-08 10:24:07 UTC 
Kernel 4.14.304 and newer can not be built.
I get the following error while compiling:

arch/x86/kernel/fpu/init.c: In function 'fpu__init_task_struct_size':
arch/x86/kernel/fpu/init.c:177: error: implicit declaration of function '_Alignof'
arch/x86/kernel/fpu/init.c:177: error: expected expression before 'struct'
arch/x86/kernel/fpu/init.c:177: error: expected expression before 'struct'
arch/x86/kernel/fpu/init.c:178: error: expected expression before 'struct'
arch/x86/kernel/fpu/init.c:178: error: expected expression before 'struct'
arch/x86/kernel/fpu/init.c:179: error: expected expression before 'struct'
arch/x86/kernel/fpu/init.c:179: error: expected expression before 'struct'

Kernel 4.14.303 is compiling/running without errors - so it must be this commit:

commit 67c6d79777cf5d3165d6d2e2d7c5e37333d1a76e
Author: YingChi Long <me@inclyc.cn>
Date:   Fri Nov 18 08:55:35 2022 +0800

    x86/fpu: Use _Alignof to avoid undefined behavior in TYPE_ALIGN
Comment 1 Borislav Petkov 2023-02-08 10:42:01 UTC 
Does it build fine if you revert this commit ontop?

What toolchain are you using to build?
Comment 2 it 2023-02-08 11:08:40 UTC 
It builds fine without this commit, yes.
I'm using standard (debian) tools for compiling (make) - but older versions because the OS is not up2date (and can not be updated).
Comment 3 Borislav Petkov 2023-02-08 11:49:47 UTC 
What does

gcc --version

say?
Comment 4 it 2023-02-08 12:13:41 UTC 
gcc (Debian 4.4.5-8) 4.4.5
Comment 5 Borislav Petkov 2023-02-08 12:59:15 UTC 
Looks like _Alignof came with gcc 4.7: https://gcc.gnu.org/gcc-4.7/changes.html

According to Documentation/Changes, min gcc version for building 4.14 is 3.2 so I guess this patch needs to be reverted from stable.

Assigning to Greg.
Comment 6 Greg Kroah-Hartman 2023-02-08 14:16:09 UTC 
Ick, yeah, that's not good.

Using old compilers usually isn't a good idea, but for this one we should probably revert it.  Can you send email to stable@vger.kernel.org and we can take it from there.
Comment 7 Greg Kroah-Hartman 2023-02-08 14:17:30 UTC 
If this showed up in 4.7, we'll need to also handle this for 4.19 if someone complains as the "minimum" gcc for that is 4.6 right now.