include/qemu/atomic.h:495:5: error: misaligned atomic operation may incur significant performance penalty (Clang 11; Ubuntu 16 i686)

[Ivan Serdyuk]

Hello.
I haven't found any "official" executables, for emulating RISC-V (32bit; 64bit) so I had to compile those myself.

I found that auto-generated build scripts, for Ninja, contained some warnings interpreted as errors:

oceanfish81@gollvm:~/Desktop/qemu/build$ ninja -j 1
[2/1977] Compiling C object libqemuutil.a.p/util_qsp.c.o
FAILED: libqemuutil.a.p/util_qsp.c.o
clang-11 -Ilibqemuutil.a.p -I. -I.. -Iqapi -Itrace -Iui -Iui/shader -I/usr/include/glib-2.0 -I/usr/lib/i386-linux-gnu/glib-2.0/include -I/usr/include/gio-unix-2.0/ -Xclang -fcolor-diagnostics -pipe -Wall -Winvalid-pch -Werror -std=gnu99 -O2 -g -m32 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -Wstrict-prototypes -Wredundant-decls -Wundef -Wwrite-strings -Wmissing-prototypes -fno-strict-aliasing -fno-common -fwrapv -Wold-style-definition -Wtype-limits -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers -Wempty-body -Wnested-externs -Wendif-labels -Wexpansion-to-defined -Wno-initializer-overrides -Wno-missing-include-dirs -Wno-shift-negative-value -Wno-string-plus-int -Wno-typedef-redefinition -Wno-tautological-type-limit-compare -Wno-psabi -fstack-protector-strong -isystem /home/oceanfish81/Desktop/qemu/linux-headers -isystem linux-headers -iquote /home/oceanfish81/Desktop/qemu/tcg/i386 -iquote . -iquote /home/oceanfish81/Desktop/qemu -iquote /home/oceanfish81/Desktop/qemu/accel/tcg -iquote /home/oceanfish81/Desktop/qemu/include -iquote /home/oceanfish81/Desktop/qemu/disas/libvixl -pthread -Wno-unused-function -fPIC -MD -MQ libqemuutil.a.p/util_qsp.c.o -MF libqemuutil.a.p/util_qsp.c.o.d -o libqemuutil.a.p/util_qsp.c.o -c ../util/qsp.c
In file included from ../util/qsp.c:62:
In file included from /home/oceanfish81/Desktop/qemu/include/qemu/thread.h:4:
In file included from /home/oceanfish81/Desktop/qemu/include/qemu/processor.h:10:
/home/oceanfish81/Desktop/qemu/include/qemu/atomic.h:495:5: error: misaligned atomic operation may incur significant performance penalty [-Werror,-Watomic-alignment]
    qatomic_set__nocheck(ptr, val);
    ^
/home/oceanfish81/Desktop/qemu/include/qemu/atomic.h:138:5: note: expanded from macro 'qatomic_set__nocheck'
    __atomic_store_n(ptr, i, __ATOMIC_RELAXED)
    ^
/home/oceanfish81/Desktop/qemu/include/qemu/atomic.h:485:12: error: misaligned atomic operation may incur significant performance penalty [-Werror,-Watomic-alignment]
    return qatomic_read__nocheck(ptr);
           ^
/home/oceanfish81/Desktop/qemu/include/qemu/atomic.h:129:5: note: expanded from macro 'qatomic_read__nocheck'
    __atomic_load_n(ptr, __ATOMIC_RELAXED)
    ^
2 errors generated.
ninja: build stopped: subcommand failed.

[Ivan Serdyuk (oceanfish81)]

$ python3.7 ../meson/meson.py --version
0.55.3

$ clang-11 --version
Ubuntu clang version 11.0.0-++20200721055954+cebd637c886-1~exp1~20200721161335.13
Target: i686-pc-linux-gnu
Thread model: posix

$ ninja --version
1.10.0.git.kitware.jobserver-1

$ uname -a
Linux laptop 4.15.0-123-generic #126~16.04.1-Ubuntu SMP Wed Oct 21 13:51:51 UTC 2020 i686 i686 i686 GNU/Linux

[Ivan Serdyuk (oceanfish81)]

Solved by removing -Werror flag

[Thomas Huth (th-huth)]

Do you still get the warning with the latest version of QEMU (v6.0)?

[Launchpad Janitor (janitor)]

[Expired for QEMU because there has been no activity for 60 days.]

[Launchpad Janitor (janitor)]

[Expired for Ubuntu because there has been no activity for 60 days.]