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Disable warn about left shifts of negative values

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It seems like there's no good reason for the compiler to exploit the
undefinedness of left shifts.  GCC explicitly documents that they do not
use at all this possibility and, while they also say this is subject
to change, they have been saying this for 10 years (since the wording
appeared in the GCC 4.0 manual).

Disable these warnings by passing in -Wno-shift-negative-value.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[pranith: forward-port part of patch to 2.7]
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
This commit is contained in:
Pranith Kumar 2016-08-09 15:02:26 -04:00 committed by Paolo Bonzini
parent 5927ed846a
commit 435405ac59
2 changed files with 5 additions and 1 deletions
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4
HACKING
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@ -158,6 +158,10 @@ painful. These are:
* you may assume that right shift of a signed integer duplicates * you may assume that right shift of a signed integer duplicates
the sign bit (ie it is an arithmetic shift, not a logical shift) the sign bit (ie it is an arithmetic shift, not a logical shift)
In addition, QEMU assumes that the compiler does not use the latitude
given in C99 and C11 to treat aspects of signed '<<' as undefined, as
documented in the GNU Compiler Collection manual starting at version 4.0.
7. Error handling and reporting 7. Error handling and reporting
7.1 Reporting errors to the human user 7.1 Reporting errors to the human user

2
configure vendored
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@ -1452,7 +1452,7 @@ fi
gcc_flags="-Wold-style-declaration -Wold-style-definition -Wtype-limits" gcc_flags="-Wold-style-declaration -Wold-style-definition -Wtype-limits"
gcc_flags="-Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers $gcc_flags" gcc_flags="-Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers $gcc_flags"
gcc_flags="-Wmissing-include-dirs -Wempty-body -Wnested-externs $gcc_flags" gcc_flags="-Wmissing-include-dirs -Wempty-body -Wnested-externs $gcc_flags"
gcc_flags="-Wendif-labels $gcc_flags" gcc_flags="-Wendif-labels -Wno-shift-negative-value $gcc_flags"
gcc_flags="-Wno-initializer-overrides $gcc_flags" gcc_flags="-Wno-initializer-overrides $gcc_flags"
gcc_flags="-Wno-string-plus-int $gcc_flags" gcc_flags="-Wno-string-plus-int $gcc_flags"
# Note that we do not add -Werror to gcc_flags here, because that would # Note that we do not add -Werror to gcc_flags here, because that would