Buildresult: linus/arm64-allmodconfig/arm64-gcc5 built on Dec 29 2020, 02:56

kisskb

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Status:	OK
Date/Time:	Dec 29 2020, 02:56
Duration:	0:24:04.008598
Builder:	ka3
Revision:	drm/edid: fix objtool warning in drm_cvt_modes() (`d652d5f1eeeb06046009f4fcb9b4542249526916)`
Target:	linus/arm64-allmodconfig/arm64-gcc5
Branch:	linus
Compiler:	arm64-gcc5 (aarch64-linux-gcc.br_real (Buildroot 2016.11-git-00613-ge98b4dd) 5.4.0 / GNU ld (GNU Binutils) 2.25.1)
Config:	allmodconfig (download)
Log:	Download original Possible warnings (3) samples/seccomp/user-trap.c:50:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] samples/seccomp/user-trap.c:83:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] lib/bitfield_kunit.c:93:1: warning: the frame size of 7440 bytes is larger than 2048 bytes [-Wframe-larger-than=] Full Log # git rev-parse -q --verify d652d5f1eeeb06046009f4fcb9b4542249526916^{commit} d652d5f1eeeb06046009f4fcb9b4542249526916 already have revision, skipping fetch # git checkout -q -f -B kisskb d652d5f1eeeb06046009f4fcb9b4542249526916 # git clean -qxdf # < git log -1 # commit d652d5f1eeeb06046009f4fcb9b4542249526916 # Author: Linus Torvalds <torvalds@linux-foundation.org> # Date: Thu Dec 17 09:27:57 2020 -0800 # # drm/edid: fix objtool warning in drm_cvt_modes() # # Commit 991fcb77f490 ("drm/edid: Fix uninitialized variable in # drm_cvt_modes()") just replaced one warning with another. # # The original warning about a possibly uninitialized variable was due to # the compiler not being smart enough to see that the case statement # actually enumerated all possible cases. And the initial fix was just to # add a "default" case that had a single "unreachable()", just to tell the # compiler that that situation cannot happen. # # However, that doesn't actually fix the fundamental reason for the # problem: the compiler still doesn't see that the existing case # statements enumerate all possibilities, so the compiler will still # generate code to jump to that unreachable case statement. It just won't # complain about an uninitialized variable any more. # # So now the compiler generates code to our inline asm marker that we told # it would not fall through, and end end result is basically random. We # have created a bridge to nowhere. # # And then, depending on the random details of just exactly what the # compiler ends up doing, 'objtool' might end up complaining about the # conditional branches (for conditions that cannot happen, and that thus # will never be taken - but if the compiler was not smart enough to figure # that out, we can't expect objtool to do so) going off in the weeds. # # So depending on how the compiler has laid out the result, you might see # something like this: # # drivers/gpu/drm/drm_edid.o: warning: objtool: do_cvt_mode() falls through to next function drm_mode_detailed.isra.0() # # and now you have a truly inscrutable warning that makes no sense at all # unless you start looking at whatever random code the compiler happened # to generate for our bare "unreachable()" statement. # # IOW, don't use "unreachable()" unless you have an _active_ operation # that generates code that actually makes it obvious that something is not # reachable (ie an UD instruction or similar). # # Solve the "compiler isn't smart enough" problem by just marking one of # the cases as "default", so that even when the compiler doesn't otherwise # see that we've enumerated all cases, the compiler will feel happy and # safe about there always being a valid case that initializes the 'width' # variable. # # This also generates better code, since now the compiler doesn't generate # comparisons for five different possibilities (the four real ones and the # one that can't happen), but just for the three real ones and "the rest" # (which is that last one). # # A smart enough compiler that sees that we cover all the cases won't care. # # Cc: Lyude Paul <lyude@redhat.com> # Cc: Ilia Mirkin <imirkin@alum.mit.edu> # Cc: Josh Poimboeuf <jpoimboe@redhat.com> # Cc: Peter Zijlstra <peterz@infradead.org> # Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> # < /opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux-gcc --version # < /opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux-ld --version # < git log --format=%s --max-count=1 d652d5f1eeeb06046009f4fcb9b4542249526916 # < make -s -j 80 ARCH=arm64 O=/kisskb/build/linus_arm64-allmodconfig_arm64-gcc5.4 CROSS_COMPILE=/opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux- allmodconfig # < make -s -j 80 ARCH=arm64 O=/kisskb/build/linus_arm64-allmodconfig_arm64-gcc5.4 CROSS_COMPILE=/opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux- help # make -s -j 80 ARCH=arm64 O=/kisskb/build/linus_arm64-allmodconfig_arm64-gcc5.4 CROSS_COMPILE=/opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux- olddefconfig # make -s -j 80 ARCH=arm64 O=/kisskb/build/linus_arm64-allmodconfig_arm64-gcc5.4 CROSS_COMPILE=/opt/cross/kisskb/br-aarch64-glibc-2016.08-613-ge98b4dd/bin/aarch64-linux- arch/arm64/Makefile:25: ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum arch/arm64/Makefile:33: LSE atomics not supported by binutils /kisskb/src/samples/seccomp/user-trap.c: In function 'send_fd': /kisskb/src/samples/seccomp/user-trap.c:50:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] ((int )CMSG_DATA(cmsg)) = fd; ^ /kisskb/src/samples/seccomp/user-trap.c: In function 'recv_fd': /kisskb/src/samples/seccomp/user-trap.c:83:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] return ((int )CMSG_DATA(cmsg)); ^ /kisskb/src/lib/bitfield_kunit.c: In function 'test_bitfields_constants': /kisskb/src/lib/bitfield_kunit.c:93:1: warning: the frame size of 7440 bytes is larger than 2048 bytes [-Wframe-larger-than=] } ^ Completed OK # rm -rf /kisskb/build/linus_arm64-allmodconfig_arm64-gcc5.4 # Build took: 0:24:04.008598

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