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| /qemu/include/qemu/ |
| H A D | compiler.h | 5a358b39f52a28a84b380c1685c93010987b3412 Thu Sep 27 15:55:38 UTC 2018 Peter Maydell <peter.maydell@linaro.org> hw/display/qxl: Suppress clang-7 warning about misaligned atomic operation
If QEMU is compiled with clang-7 it results in the warning:
hw/display/qxl.c:1884:19: error: misaligned or large atomic operation
may incur significant performance penalty [-Werror,-Watomic-alignment]
old_pending = atomic_fetch_or(&d->ram->int_pending, le_events);
^
This is because the Spice headers forgot to define the QXLRam struct
with the '__aligned__(4)' attribute. clang 7 and newer will thus
warn that the access here to int_pending might not be 4-aligned
(because the QXLRam object d->ram points at might start at a
misaligned address). In fact we set up d->ram in init_qxl_ram() so
it always starts at a 4K boundary, so we know the atomic access here
is OK.
Newer Spice versions (with Spice commit
beda5ec7a6848be20c0cac2a9a8ef2a41e8069c1) will fix the bug;
for older Spice versions, work around it by telling the compiler
explicitly that the alignment is OK using __builtin_assume_aligned().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180927155538.699-1-peter.maydell@linaro.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
|
| /qemu/hw/display/ |
| H A D | qxl.c | 5a358b39f52a28a84b380c1685c93010987b3412 Thu Sep 27 15:55:38 UTC 2018 Peter Maydell <peter.maydell@linaro.org> hw/display/qxl: Suppress clang-7 warning about misaligned atomic operation
If QEMU is compiled with clang-7 it results in the warning:
hw/display/qxl.c:1884:19: error: misaligned or large atomic operation
may incur significant performance penalty [-Werror,-Watomic-alignment]
old_pending = atomic_fetch_or(&d->ram->int_pending, le_events);
^
This is because the Spice headers forgot to define the QXLRam struct
with the '__aligned__(4)' attribute. clang 7 and newer will thus
warn that the access here to int_pending might not be 4-aligned
(because the QXLRam object d->ram points at might start at a
misaligned address). In fact we set up d->ram in init_qxl_ram() so
it always starts at a 4K boundary, so we know the atomic access here
is OK.
Newer Spice versions (with Spice commit
beda5ec7a6848be20c0cac2a9a8ef2a41e8069c1) will fix the bug;
for older Spice versions, work around it by telling the compiler
explicitly that the alignment is OK using __builtin_assume_aligned().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180927155538.699-1-peter.maydell@linaro.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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