Buildresult: linus/mips-defconfig/mips-gcc8 built on Dec 18 2020, 05:49

kisskb

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Status:	OK
Date/Time:	Dec 18 2020, 05:49
Duration:	0:02:11.417105
Builder:	ka3
Revision:	drm/edid: fix objtool warning in drm_cvt_modes() (`d652d5f1eeeb06046009f4fcb9b4542249526916)`
Target:	linus/mips-defconfig/mips-gcc8
Branch:	linus
Compiler:	mips-gcc8 (mips-linux-gcc (GCC) 8.1.0 / GNU ld (GNU Binutils) 2.30)
Config:	defconfig (download)
Log:	Download original No warnings found in log. 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/korg/gcc-8.1.0-nolibc/mips-linux/bin/mips-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/mips-linux/bin/mips-linux-ld --version # < git log --format=%s --max-count=1 d652d5f1eeeb06046009f4fcb9b4542249526916 # < make -s -j 80 ARCH=mips O=/kisskb/build/linus_mips-defconfig_mips-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/mips-linux/bin/mips-linux- defconfig # < make -s -j 80 ARCH=mips O=/kisskb/build/linus_mips-defconfig_mips-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/mips-linux/bin/mips-linux- help # make -s -j 80 ARCH=mips O=/kisskb/build/linus_mips-defconfig_mips-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/mips-linux/bin/mips-linux- olddefconfig # make -s -j 80 ARCH=mips O=/kisskb/build/linus_mips-defconfig_mips-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/mips-linux/bin/mips-linux- FIT description: Linux 5.10.0-gd652d5f1eeeb Created: Fri Dec 18 05:51:43 2020 Image 0 (kernel@0) Description: Linux 5.10.0-gd652d5f1eeeb Created: Fri Dec 18 05:51:43 2020 Type: Kernel Image Compression: gzip compressed Data Size: 5183826 Bytes = 5062.33 KiB = 4.94 MiB Architecture: MIPS OS: Linux Load Address: 0x80100000 Entry Point: 0x8098deac Hash algo: sha1 Hash value: 04a95f3a6c9db19d5e840e1808c1aefcb1fde5e5 Image 1 (fdt@boston) Description: img,boston Device Tree Created: Fri Dec 18 05:51:43 2020 Type: Flat Device Tree Compression: uncompressed Data Size: 3793 Bytes = 3.70 KiB = 0.00 MiB Architecture: MIPS Hash algo: sha1 Hash value: 4799f50d688573234da6e9d7701234d394759ef4 Image 2 (fdt@ni169445) Description: NI 169445 device tree Created: Fri Dec 18 05:51:43 2020 Type: Flat Device Tree Compression: uncompressed Data Size: 1871 Bytes = 1.83 KiB = 0.00 MiB Architecture: MIPS Hash algo: sha1 Hash value: 51b89b31605ee62038c8468c429af091dfc75ec7 Image 3 (fdt@ocelot_pcb123) Description: MSCC Ocelot PCB123 Device Tree Created: Fri Dec 18 05:51:43 2020 Type: Flat Device Tree Compression: uncompressed Data Size: 4659 Bytes = 4.55 KiB = 0.00 MiB Architecture: MIPS Hash algo: sha1 Hash value: 5bcb6e4f21e8e5372544aa130b3bd097355a9050 Image 4 (fdt@ocelot_pcb120) Description: MSCC Ocelot PCB120 Device Tree Created: Fri Dec 18 05:51:43 2020 Type: Flat Device Tree Compression: uncompressed Data Size: 5418 Bytes = 5.29 KiB = 0.01 MiB Architecture: MIPS Hash algo: sha1 Hash value: 93d882f2009a217e0fa9dab94788535ed2be8476 Image 5 (fdt@xilfpga) Description: MIPSfpga (xilfpga) Device Tree Created: Fri Dec 18 05:51:43 2020 Type: Flat Device Tree Compression: uncompressed Data Size: 2708 Bytes = 2.64 KiB = 0.00 MiB Architecture: MIPS Hash algo: sha1 Hash value: 63d058b780f65e22da30f0a183433765f1807f1d Default Configuration: 'conf@default' Configuration 0 (conf@default) Description: Generic Linux kernel Kernel: kernel@0 Configuration 1 (conf@boston) Description: Boston Linux kernel Kernel: kernel@0 FDT: fdt@boston Configuration 2 (conf@ni169445) Description: NI 169445 Linux Kernel Kernel: kernel@0 FDT: fdt@ni169445 Configuration 3 (conf@ocelot_pcb123) Description: Ocelot Linux kernel Kernel: kernel@0 FDT: fdt@ocelot_pcb123 Configuration 4 (conf@ocelot_pcb120) Description: Ocelot Linux kernel Kernel: kernel@0 FDT: fdt@ocelot_pcb120 Configuration 5 (conf@xilfpga) Description: MIPSfpga Linux kernel Kernel: kernel@0 FDT: fdt@xilfpga Completed OK # rm -rf /kisskb/build/linus_mips-defconfig_mips-gcc8 # Build took: 0:02:11.417105

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