linux-kernel - Re: New -Werror=restrict error with incremental gcc

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Message-ID: <53714ddf-1b2d-295b-e364-3330f1d9c48c@redhat.com>
Date:   Thu, 15 Mar 2018 08:06:26 -0700
From:   Laura Abbott <labbott@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Wang Nan <wangnan0@...wei.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: New -Werror=restrict error with incremental gcc

On 03/15/2018 07:30 AM, Arnaldo Carvalho de Melo wrote:
> Em Wed, Mar 14, 2018 at 02:19:41PM -0700, Laura Abbott escreveu:
>> Hi,
>>
>> Fedora picked up a new gcc (8.0.1-0.18.fc29) and it seems to have introduced a new error:
>>
>>    gcc -Wp,-MD,/home/labbott/linux/tools/objtool/.str_error_r.o.d -Wp,-MT,/home/labbott/linux/tools/objtool/str_error_r.o -Wall -Werror -Wbad-function-cast -Wdeclaration-after-statement -Wformat-security -Wformat-y2k -Winit-self -Wmissing-declarations -Wmissing-prototypes -Wnested-externs -Wno-system-headers -Wold-style-definition -Wpacked -Wredundant-decls -Wshadow -Wstrict-prototypes -Wswitch-default -Wswitch-enum -Wundef -Wwrite-strings -Wformat -Wstrict-aliasing=3 -Wno-switch-default -Wno-switch-enum -Wno-packed -fomit-frame-pointer -O2 -g -I/home/labbott/linux/tools/include -I/home/labbott/linux/tools/arch/x86/include/uapi -I/home/labbott/linux/tools/objtool/arch/x86/include -I/home/labbott/linux/tools/lib -D"BUILD_STR(s)=#s" -c -o /home/labbott/linux/tools/objtool/str_error_r.o ../lib/str_error_r.c
>> ../lib/str_error_r.c: In function ‘str_error_r’:
>> ../lib/str_error_r.c:25:3: error: passing argument 1 to restrict-qualified parameter aliases with argument 5 [-Werror=restrict]
>>     snprintf(buf, buflen, "INTERNAL ERROR: strerror_r(%d, %p, %zd)=%d", errnum, buf, buflen, err);
>>     ^~
>>
>> This looks like gcc is now warning about the aliasing from printing out buf
>> while printing to the buffer. I can work around this pretty easily but I
>> know people have strong opinions about gcc warnings. Any thoughts?
> 
> I couldn't reproduce it here:
> 
> [perfbuilder@...646cdb12b perf]$ gcc -v
> Using built-in specs.
> COLLECT_GCC=gcc
> COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/8/lto-wrapper
> OFFLOAD_TARGET_NAMES=nvptx-none
> OFFLOAD_TARGET_DEFAULT=1
> Target: x86_64-redhat-linux
> Configured with: ../configure --enable-bootstrap
> --enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --prefix=/usr
> --mandir=/usr/share/man --infodir=/usr/share/info
> --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
> --enable-threads=posix --enable-checking=release --enable-multilib
> --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
> --enable-gnu-unique-object --enable-linker-build-id
> --with-gcc-major-version-only --with-linker-hash-style=gnu
> --enable-plugin --enable-initfini-array --with-isl --enable-libmpx
> --enable-offload-targets=nvptx-none --without-cuda-driver
> --enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686
> --build=x86_64-redhat-linux
> Thread model: posix
> gcc version 8.0.1 20180310 (Red Hat 8.0.1-0.17) (GCC)
> [perfbuilder@...646cdb12b perf]$ rpm -q gcc
> gcc-8.0.1-0.17.fc29.x86_64
> [perfbuilder@...646cdb12b perf]$
> 
> [perfbuilder@...646cdb12b perf]$ make O=/tmp/build/kernel/
> make[1]: Entering directory '/tmp/build/kernel'
>    CHK     include/config/kernel.release
>    Using /git/perf as source for kernel
>    GEN     ./Makefile
>    CHK     include/generated/uapi/linux/version.h
>    CHK     include/generated/utsrelease.h
>    CHK     include/generated/bounds.h
>    CHK     include/generated/timeconst.h
>    CHK     include/generated/asm-offsets.h
>    CALL    /git/perf/scripts/checksyscalls.sh
>    DESCEND  objtool
>    CC       /tmp/build/kernel/tools/objtool/str_error_r.o
>    LD       /tmp/build/kernel/tools/objtool/objtool-in.o
>    LINK     /tmp/build/kernel/tools/objtool/objtool
>    CHK     scripts/mod/devicetable-offsets.h
>    HOSTCC  scripts/asn1_compiler
> 
> 
> :-\
> 
> But I noticed some of those warnings and started action on then for
> tools/perf, things like:
> 
> "perf annotate: Use asprintf when formatting objdump command line"
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/commit/?id=f22ed8ad2ca0
> 
> - Arnaldo
> 

This only showed up with the very latest rawhide snapshot, .17 worked and
.18 started failing. I had to download .18 manually to test locally
https://koji.fedoraproject.org/koji/packageinfo?packageID=40

Thanks,
Laura