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[Qemu-devel] [PULL 06/14] Disable warn about left shifts of negative val
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PULL 06/14] Disable warn about left shifts of negative values |
Date: |
Wed, 10 Aug 2016 15:57:09 +0200 |
From: Pranith Kumar <address@hidden>
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 <address@hidden>
Cc: Markus Armbruster <address@hidden>
Cc: Laszlo Ersek <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
[pranith: forward-port part of patch to 2.7]
Signed-off-by: Pranith Kumar <address@hidden>
---
HACKING | 4 ++++
configure | 2 +-
2 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/HACKING b/HACKING
index 058aa8f..20a9101 100644
--- a/HACKING
+++ b/HACKING
@@ -158,6 +158,10 @@ painful. These are:
* you may assume that right shift of a signed integer duplicates
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
7.1 Reporting errors to the human user
diff --git a/configure b/configure
index f57fcc6..8d84919 100755
--- a/configure
+++ b/configure
@@ -1452,7 +1452,7 @@ fi
gcc_flags="-Wold-style-declaration -Wold-style-definition -Wtype-limits"
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="-Wendif-labels $gcc_flags"
+gcc_flags="-Wendif-labels -Wno-shift-negative-value $gcc_flags"
gcc_flags="-Wno-initializer-overrides $gcc_flags"
gcc_flags="-Wno-string-plus-int $gcc_flags"
# Note that we do not add -Werror to gcc_flags here, because that would
--
1.8.3.1
- [Qemu-devel] [PULL 00/14] checkpatch, warnings and other fixes, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 03/14] optionrom: add -fno-stack-protector, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 04/14] optionrom: fix compilation with mingw docker target, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 02/14] build-sys: fix building with make CFLAGS=.. argument, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 01/14] linuxboot_dma: avoid guest ABI breakage on gcc vs. clang compilation, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 05/14] atomic: strip "const" from variables declared with typeof, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 06/14] Disable warn about left shifts of negative values,
Paolo Bonzini <=
- [Qemu-devel] [PULL 07/14] clang: Fix warning reg. expansion to 'defined', Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 08/14] checkpatch: ignore automatically imported Linux headers, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 11/14] checkpatch: check for CVS keywords on all sources, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 10/14] checkpatch: tweak the files in which TABs are checked, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 09/14] timer: set vm_clock disabled default, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 12/14] CODING_STYLE, checkpatch: update line length rules, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 13/14] checkpatch: bump most warnings to errors, Paolo Bonzini, 2016/08/10
- [Qemu-devel] [PULL 14/14] checkpatch: default to success if only warnings, Paolo Bonzini, 2016/08/10
- Re: [Qemu-devel] [PULL 00/14] checkpatch, warnings and other fixes, Peter Maydell, 2016/08/10