# 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 # 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 # Cc: Ilia Mirkin # Cc: Josh Poimboeuf # Cc: Peter Zijlstra # Signed-off-by: Linus Torvalds # < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux-ld --version # < git log --format=%s --max-count=1 d652d5f1eeeb06046009f4fcb9b4542249526916 # < make -s -j 120 ARCH=ia64 O=/kisskb/build/linus_ia64-defconfig_ia64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux- defconfig arch/ia64/configs/generic_defconfig:58:warning: override: reassigning to symbol ATA arch/ia64/configs/generic_defconfig:59:warning: override: reassigning to symbol ATA_PIIX # make -s -j 120 ARCH=ia64 O=/kisskb/build/linus_ia64-defconfig_ia64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux- :1511:2: warning: #warning syscall clone3 not implemented [-Wcpp] In file included from /kisskb/src/include/linux/numa.h:25:0, from /kisskb/src/include/linux/async.h:13, from /kisskb/src/kernel/async.c:47: /kisskb/src/arch/ia64/include/asm/sparsemem.h:14:40: warning: "PAGE_SHIFT" is not defined [-Wundef] #if ((CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS) ^ In file included from /kisskb/src/include/linux/gfp.h:6:0, from /kisskb/src/include/linux/xarray.h:14, from /kisskb/src/include/linux/radix-tree.h:19, from /kisskb/src/include/linux/idr.h:15, from /kisskb/src/include/linux/kernfs.h:13, from /kisskb/src/include/linux/sysfs.h:16, from /kisskb/src/include/linux/kobject.h:20, from /kisskb/src/include/linux/energy_model.h:7, from /kisskb/src/include/linux/device.h:16, from /kisskb/src/include/linux/async.h:14, from /kisskb/src/kernel/async.c:47: /kisskb/src/include/linux/mmzone.h:1156:2: error: #error Allocator MAX_ORDER exceeds SECTION_SIZE #error Allocator MAX_ORDER exceeds SECTION_SIZE ^ make[2]: *** [/kisskb/src/scripts/Makefile.build:279: kernel/async.o] Error 1 make[2]: *** Waiting for unfinished jobs.... make[1]: *** [/kisskb/src/Makefile:1805: kernel] Error 2 make[1]: *** Waiting for unfinished jobs.... /kisskb/src/drivers/gpu/drm/ttm/ttm_pool.c:240:21: warning: 'ttm_pool_type_count' defined but not used [-Wunused-function] static unsigned int ttm_pool_type_count(struct ttm_pool_type *pt) ^ In file included from /kisskb/src/arch/ia64/include/uapi/asm/intrinsics.h:22:0, from /kisskb/src/arch/ia64/include/asm/intrinsics.h:11, from /kisskb/src/arch/ia64/include/asm/timex.h:14, from /kisskb/src/include/linux/timex.h:65, from /kisskb/src/include/linux/time32.h:13, from /kisskb/src/include/linux/time.h:60, from /kisskb/src/fs/nfs/read.c:11: /kisskb/src/fs/nfs/read.c: In function 'nfs_read_completion': /kisskb/src/arch/ia64/include/uapi/asm/cmpxchg.h:57:2: warning: value computed is not used [-Wunused-value] ((__typeof__(*(ptr))) __xchg((unsigned long) (x), (ptr), sizeof(*(ptr)))) ^ /kisskb/src/fs/nfs/read.c:196:5: note: in expansion of macro 'xchg' xchg(&nfs_req_openctx(req)->error, error); ^ /kisskb/src/fs/nfs/read.c: In function 'nfs_readpage': /kisskb/src/arch/ia64/include/uapi/asm/cmpxchg.h:57:2: warning: value computed is not used [-Wunused-value] ((__typeof__(*(ptr))) __xchg((unsigned long) (x), (ptr), sizeof(*(ptr)))) ^ /kisskb/src/fs/nfs/read.c:355:2: note: in expansion of macro 'xchg' xchg(&ctx->error, 0); ^ In file included from /kisskb/src/include/linux/numa.h:25:0, from /kisskb/src/include/linux/async.h:13, from /kisskb/src/drivers/base/bus.c:11: /kisskb/src/arch/ia64/include/asm/sparsemem.h:14:40: warning: "PAGE_SHIFT" is not defined [-Wundef] #if ((CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS) ^ In file included from /kisskb/src/include/linux/gfp.h:6:0, from /kisskb/src/include/linux/xarray.h:14, from /kisskb/src/include/linux/radix-tree.h:19, from /kisskb/src/include/linux/idr.h:15, from /kisskb/src/include/linux/kernfs.h:13, from /kisskb/src/include/linux/sysfs.h:16, from /kisskb/src/include/linux/kobject.h:20, from /kisskb/src/include/linux/energy_model.h:7, from /kisskb/src/include/linux/device.h:16, from /kisskb/src/include/linux/async.h:14, from /kisskb/src/drivers/base/bus.c:11: /kisskb/src/include/linux/mmzone.h:1156:2: error: #error Allocator MAX_ORDER exceeds SECTION_SIZE #error Allocator MAX_ORDER exceeds SECTION_SIZE ^ make[3]: *** [/kisskb/src/scripts/Makefile.build:279: drivers/base/bus.o] Error 1 make[3]: *** Waiting for unfinished jobs.... In file included from /kisskb/src/include/linux/numa.h:25:0, from /kisskb/src/include/linux/nodemask.h:96, from /kisskb/src/include/linux/mount.h:15, from /kisskb/src/fs/pnode.c:9: /kisskb/src/arch/ia64/include/asm/sparsemem.h:14:40: warning: "PAGE_SHIFT" is not defined [-Wundef] #if ((CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS) ^ In file included from /kisskb/src/include/linux/numa.h:25:0, from /kisskb/src/include/linux/nodemask.h:96, from /kisskb/src/include/linux/mount.h:15, from /kisskb/src/fs/utimes.c:3: /kisskb/src/arch/ia64/include/asm/sparsemem.h:14:40: warning: "PAGE_SHIFT" is not defined [-Wundef] #if ((CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS) ^ In file included from /kisskb/src/include/linux/gfp.h:6:0, from /kisskb/src/include/linux/xarray.h:14, from /kisskb/src/include/linux/radix-tree.h:19, from /kisskb/src/include/linux/fs.h:15, from /kisskb/src/fs/pnode.c:10: /kisskb/src/include/linux/mmzone.h:1156:2: error: #error Allocator MAX_ORDER exceeds SECTION_SIZE #error Allocator MAX_ORDER exceeds SECTION_SIZE ^ make[2]: *** [/kisskb/src/scripts/Makefile.build:279: fs/pnode.o] Error 1 make[2]: *** Waiting for unfinished jobs.... In file included from /kisskb/src/include/linux/gfp.h:6:0, from /kisskb/src/include/linux/xarray.h:14, from /kisskb/src/include/linux/radix-tree.h:19, from /kisskb/src/include/linux/fs.h:15, from /kisskb/src/include/linux/namei.h:5, from /kisskb/src/fs/utimes.c:4: /kisskb/src/include/linux/mmzone.h:1156:2: error: #error Allocator MAX_ORDER exceeds SECTION_SIZE #error Allocator MAX_ORDER exceeds SECTION_SIZE ^ make[2]: *** [/kisskb/src/scripts/Makefile.build:279: fs/utimes.o] Error 1 make[2]: *** [/kisskb/src/scripts/Makefile.build:496: drivers/base] Error 2 make[2]: *** Waiting for unfinished jobs.... In file included from /kisskb/src/include/linux/numa.h:25:0, from /kisskb/src/include/linux/async.h:13, from /kisskb/src/drivers/acpi/battery.c:13: /kisskb/src/arch/ia64/include/asm/sparsemem.h:14:40: warning: "PAGE_SHIFT" is not defined [-Wundef] #if ((CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS) ^ In file included from /kisskb/src/include/linux/gfp.h:6:0, from /kisskb/src/include/linux/xarray.h:14, from /kisskb/src/include/linux/radix-tree.h:19, from /kisskb/src/include/linux/idr.h:15, from /kisskb/src/include/linux/kernfs.h:13, from /kisskb/src/include/linux/sysfs.h:16, from /kisskb/src/include/linux/kobject.h:20, from /kisskb/src/include/linux/energy_model.h:7, from /kisskb/src/include/linux/device.h:16, from /kisskb/src/include/linux/async.h:14, from /kisskb/src/drivers/acpi/battery.c:13: /kisskb/src/include/linux/mmzone.h:1156:2: error: #error Allocator MAX_ORDER exceeds SECTION_SIZE #error Allocator MAX_ORDER exceeds SECTION_SIZE ^ make[3]: *** [/kisskb/src/scripts/Makefile.build:279: drivers/acpi/battery.o] Error 1 make[3]: *** Waiting for unfinished jobs.... In file included from /kisskb/src/include/linux/numa.h:25:0, from /kisskb/src/include/linux/nodemask.h:96, from /kisskb/src/lib/nodemask.c:2: /kisskb/src/arch/ia64/include/asm/sparsemem.h:14:40: warning: "PAGE_SHIFT" is not defined [-Wundef] #if ((CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS) ^ In file included from /kisskb/src/include/linux/gfp.h:6:0, from /kisskb/src/include/linux/umh.h:4, from /kisskb/src/include/linux/kmod.h:9, from /kisskb/src/include/linux/module.h:16, from /kisskb/src/lib/nodemask.c:3: /kisskb/src/include/linux/mmzone.h:1156:2: error: #error Allocator MAX_ORDER exceeds SECTION_SIZE #error Allocator MAX_ORDER exceeds SECTION_SIZE ^ make[2]: *** [/kisskb/src/scripts/Makefile.build:280: lib/nodemask.o] Error 1 make[2]: *** Waiting for unfinished jobs.... make[1]: *** [/kisskb/src/Makefile:1805: lib] Error 2 make[2]: *** [/kisskb/src/scripts/Makefile.build:496: drivers/acpi] Error 2 make[1]: *** [/kisskb/src/Makefile:1805: fs] Error 2 make[1]: *** [/kisskb/src/Makefile:1805: drivers] Error 2 make: *** [Makefile:185: __sub-make] Error 2 Command 'make -s -j 120 ARCH=ia64 O=/kisskb/build/linus_ia64-defconfig_ia64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/ia64-linux/bin/ia64-linux- ' returned non-zero exit status 2 # rm -rf /kisskb/build/linus_ia64-defconfig_ia64-gcc4.9 # Build took: 0:01:04.168860