Re: [Qemu-devel] [PULL 00/11] Ide patches

[Mark Cave-Ayland]

On 18/09/17 19:14, Peter Maydell wrote:

> On 18 September 2017 at 19:00, Peter Maydell <address@hidden> wrote:
>> On 18 September 2017 at 18:55, John Snow <address@hidden> wrote:
>>> On 09/16/2017 10:34 AM, Peter Maydell wrote:
>>>> Hi; I'm afraid this doesn't build with clang:
>>>>
>>>> /home/petmay01/linaro/qemu-for-merges/hw/ide/core.c:70:15: error:
>>>> comparison of unsigned enum expression >= 0 is always true
>>>> [-Werror,-Wtautological-compare]
>>>>     if (enval >= 0 && enval < IDE_DMA__COUNT) {
>>>>         ~~~~~ ^  ~
>>>> 1 error generated
> 
> 
>> I think you could argue that it would at least be helpful
>> if clang didn't warn about comparisons that only happen
>> to be useless for this particular platform/impdef choice
>> but are useful for the same code compiled with a different
>> compiler.
> 
> A bit of googling and some experimentation reveals that
> clang deliberately suppresses this warning in the special
> case of comparing against an enum value which happens to
> be zero (but not for literal constant zero!). So this will
> be fine:
>    if (enval >= IDE_DMA_READ && enval < IDE_DMA__COUNT)
> 
> (or more sensibly you'd want to define an enum constant
> for IDE_DMA__FIRST or something rather than relying on
> READ being 0.)
> 
> (found here:
> http://clang-developers.42468.n3.nabble.com/Possibly-invalid-enum-tautology-warning-td3233140.html
> )

Doing a git pull and even with the applied version of this patch I get a
build failure on my local gcc-4.7:

cc -I/home/build/src/qemu/git/qemu/hw/ide -Ihw/ide
-I/home/build/src/qemu/git/qemu/tcg
-I/home/build/src/qemu/git/qemu/tcg/i386
-I/home/build/src/qemu/git/qemu/linux-headers
-I/home/build/src/qemu/git/qemu/linux-headers -I.
-I/home/build/src/qemu/git/qemu
-I/home/build/src/qemu/git/qemu/accel/tcg
-I/home/build/src/qemu/git/qemu/include -I/usr/include/pixman-1
-I/home/build/src/qemu/git/qemu/dtc/libfdt -Werror -pthread
-I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include
-m64 -mcx16 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE
-Wstrict-prototypes -Wredundant-decls -Wall -Wundef -Wwrite-strings
-Wmissing-prototypes -fno-strict-aliasing -fno-common -fwrapv
-Wendif-labels -Wno-missing-include-dirs -Wempty-body -Wnested-externs
-Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers
-Wold-style-declaration -Wold-style-definition -Wtype-limits
-fstack-protector-all -I/usr/include/p11-kit-1
-I/usr/include/libpng12   -I/home/build/src/qemu/git/qemu/tests -MMD -MP
-MT hw/ide/core.o -MF hw/ide/core.d -O2 -U_FORTIFY_SOURCE
-D_FORTIFY_SOURCE=2 -g   -c -o hw/ide/core.o hw/ide/core.c
hw/ide/core.c: In function ‘IDE_DMA_CMD_str’:
hw/ide/core.c:71:5: error: comparison of unsigned expression >= 0 is
always true [-Werror=type-limits]
cc1: all warnings being treated as errors
make: *** [hw/ide/core.o] Error 1

Are there any other workarounds for this at all?


ATB,

Mark.