There are few of them, but this one is OK. The value is always initialized, and apparantly GCC is able to prove it sometimes.
Actually, most of the warnings I get with -Og are false alarms. Only very few of them are real. That's why I think we should rather explicitly turn on the magic yet unknown option, than to specify unnecessary default values to silence GCC. Or a least make maybe-uninitialized onlu a warning. What's even more strange, now I cannot reproduce it with -O3 neither. But I'm pretty sure it was -O3. Also, I wasn't the first to notice this behavior, Petr Mánek did (CCing him). Maybe he can add some details from his side. $ amd64-unknown-elf-gcc -v Using built-in specs. COLLECT_GCC=bin/amd64-unknown-elf-gcc COLLECT_LTO_WRAPPER=/home/ohlavaty/.local/cross/amd64-unknown-elf/bin/../libexec/gcc/amd64-unknown-elf/7.1.0/lto-wrapper Target: amd64-unknown-elf Configured with: /home/ohlavaty/projects/helenos/xhci/amd64-unknown-elf/gcc-7.1.0/configure --target=amd64-unknown-elf --prefix=/home/ohlavaty/.local/cross//amd64-unknown-elf --program-prefix=amd64-unknown-elf- --with-gnu-as --with-gnu-ld --disable-nls --disable-threads --enable-languages=c,objc,c++,obj-c++ --disable-multilib --disable-libgcj --without-headers --disable-shared --enable-lto --disable-werror Thread model: single gcc version 7.1.0 (GCC) OH On 20.10., Jiří Zárevúcky wrote: > The weirdest part that as far as I can tell, those are legit bugs. > > On my end, I get no warnings whatsoever. The whole build is clean. > > On 20 October 2017 at 01:17, Ondřej Hlavatý <[email protected]> wrote: > > OK, this one is just too weird. It seems GCC turns off some heuristics. > > It might be a better option to find out how to turn it back on on lower > > optimization levels. > > > > See this (command taken from make output, optimization moved to the very > > end): > > > > $ cd uspace/drv/bus/pci/pciintel > > $ $CROSS_PREFIX/amd64-unknown-elf/bin/amd64-unknown-elf-gcc > > -I../../../../lib/c/include -I../../../../lib/c/arch/amd64/include > > -I../../../../../abi/include -imacros ../../../../../config.h > > -ffreestanding -fno-builtin -nostdlib -nostdinc -fexec-charset=UTF-8 > > -finput-charset=UTF-8 -D__LE__ -Werror -fno-omit-frame-pointer > > -ffunction-sections -Wall -Wextra -Wno-clobbered -Wno-unused-parameter > > -Wmissing-prototypes -std=gnu99 -Werror-implicit-function-declaration > > -Wwrite-strings -pipe -mno-tls-direct-seg-refs -g > > -I../../../../lib/drv/include -c pci.c -o pci.o -O0 > > > > $ $CROSS_PREFIX/amd64-unknown-elf/bin/amd64-unknown-elf-gcc > > -I../../../../lib/c/include -I../../../../lib/c/arch/amd64/include > > -I../../../../../abi/include -imacros ../../../../../config.h > > -ffreestanding -fno-builtin -nostdlib -nostdinc -fexec-charset=UTF-8 > > -finput-charset=UTF-8 -D__LE__ -Werror -fno-omit-frame-pointer > > -ffunction-sections -Wall -Wextra -Wno-clobbered -Wno-unused-parameter > > -Wmissing-prototypes -std=gnu99 -Werror-implicit-function-declaration > > -Wwrite-strings -pipe -mno-tls-direct-seg-refs -g > > -I../../../../lib/drv/include -c pci.c -o pci.o -O1 > > > > pci.c: In function 'pci_conf_write': > > pci.c:322:7: error: 'val' may be used uninitialized in this function > > [-Werror=maybe-uninitialized] > > val &= ~(0xffU << ((reg & 3) * 8)); > > ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > cc1: all warnings being treated as errors > > $ $CROSS_PREFIX/amd64-unknown-elf/bin/amd64-unknown-elf-gcc > > -I../../../../lib/c/include -I../../../../lib/c/arch/amd64/include > > -I../../../../../abi/include -imacros ../../../../../config.h > > -ffreestanding -fno-builtin -nostdlib -nostdinc -fexec-charset=UTF-8 > > -finput-charset=UTF-8 -D__LE__ -Werror -fno-omit-frame-pointer > > -ffunction-sections -Wall -Wextra -Wno-clobbered -Wno-unused-parameter > > -Wmissing-prototypes -std=gnu99 -Werror-implicit-function-declaration > > -Wwrite-strings -pipe -mno-tls-direct-seg-refs -g > > -I../../../../lib/drv/include -c pci.c -o pci.o -O2 > > > > $ $CROSS_PREFIX/amd64-unknown-elf/bin/amd64-unknown-elf-gcc > > -I../../../../lib/c/include -I../../../../lib/c/arch/amd64/include > > -I../../../../../abi/include -imacros ../../../../../config.h > > -ffreestanding -fno-builtin -nostdlib -nostdinc -fexec-charset=UTF-8 > > -finput-charset=UTF-8 -D__LE__ -Werror -fno-omit-frame-pointer > > -ffunction-sections -Wall -Wextra -Wno-clobbered -Wno-unused-parameter > > -Wmissing-prototypes -std=gnu99 -Werror-implicit-function-declaration > > -Wwrite-strings -pipe -mno-tls-direct-seg-refs -g > > -I../../../../lib/drv/include -c pci.c -o pci.o -O3 > > > > $ $CROSS_PREFIX/amd64-unknown-elf/bin/amd64-unknown-elf-gcc > > -I../../../../lib/c/include -I../../../../lib/c/arch/amd64/include > > -I../../../../../abi/include -imacros ../../../../../config.h > > -ffreestanding -fno-builtin -nostdlib -nostdinc -fexec-charset=UTF-8 > > -finput-charset=UTF-8 -D__LE__ -Werror -fno-omit-frame-pointer > > -ffunction-sections -Wall -Wextra -Wno-clobbered -Wno-unused-parameter > > -Wmissing-prototypes -std=gnu99 -Werror-implicit-function-declaration > > -Wwrite-strings -pipe -mno-tls-direct-seg-refs -g > > -I../../../../lib/drv/include -c pci.c -o pci.o -Ofast > > > > $ $CROSS_PREFIX/amd64-unknown-elf/bin/amd64-unknown-elf-gcc > > -I../../../../lib/c/include -I../../../../lib/c/arch/amd64/include > > -I../../../../../abi/include -imacros ../../../../../config.h > > -ffreestanding -fno-builtin -nostdlib -nostdinc -fexec-charset=UTF-8 > > -finput-charset=UTF-8 -D__LE__ -Werror -fno-omit-frame-pointer > > -ffunction-sections -Wall -Wextra -Wno-clobbered -Wno-unused-parameter > > -Wmissing-prototypes -std=gnu99 -Werror-implicit-function-declaration > > -Wwrite-strings -pipe -mno-tls-direct-seg-refs -g > > -I../../../../lib/drv/include -c pci.c -o pci.o -Og > > > > pci.c: In function 'pci_conf_write': > > pci.c:322:7: error: 'val' may be used uninitialized in this function > > [-Werror=maybe-uninitialized] > > val &= ~(0xffU << ((reg & 3) * 8)); > > > > How does this behave on your end? > > > > OH > > > > On 20.10., Jiří Zárevúcky wrote: > >> Weird! > >> > >> Whatever the reason for suspicious silence here, this needs to be fixed. > >> It would be great if you could fix all the warnings you are getting. > >> I'll merge your directive as soon as you have it. > >> > >> Thanks! > >> > >> > >> On 20 October 2017 at 00:20, Ondřej Hlavatý <[email protected]> wrote: > >> > Hi, > >> > > >> > On 19.10., Jiří Zárevúcky wrote: > >> >> Could you elaborate on your setup? > >> >> In particular, do you use the proper cross-compiler, as built using > >> >> toolchain.sh? > >> > > >> > I just installed fresh toolchain, distclean, loaded amd64 defaults and > >> > it happened. Strangely, no warnings are reported with -O2. > >> > > >> >> Also, did you add any additional compiler flags? > >> > > >> > No. > >> > > >> >> Any other changes? Differences from default settings? > >> > > >> > My CROSS_PREFIX is set to dir in my home, not the system default. It > >> > still contains the old toolchain, if that could matter. > >> > > >> > I can't think of any other difference - I don't even use the mainline > >> > checkout while working on xhci. > >> > > >> > OH > >> > > >> >> On 19 October 2017 at 23:40, Ondřej Hlavatý <[email protected]> wrote: > >> >> > Well, it seems that the patch is sufficient only when compiling with > >> >> > -O3. There are a lot of other warnings with -Og. It is probably worth > >> >> > checking them all (possibly with -O0) and fixing/muting them at once. > >> >> > > >> >> > Shall I prepare that? > >> >> > > >> >> > OH > >> >> > > >> >> > On 19.10., Ondra Hlavatý wrote: > >> >> >> Hi all, > >> >> >> > >> >> >> When building current mainline with freshly downloaded toolchain, GCC > >> >> >> 7.1.0 complains about uninitialized variables. First of them is real > >> >> >> (extent.c), the second is not, but it's probably too hard for GCC to > >> >> >> infer. > >> >> >> > >> >> >> Hope you're enjoing the hangout. > >> >> >> Ondra Hlavatý > >> >> > > >> >> >> # Bazaar merge directive format 2 (Bazaar 0.90) > >> >> >> # revision_id: [email protected] > >> >> >> # target_branch: bzr://bzr.helenos.org/mainline/ > >> >> >> # testament_sha1: 5343d00f1a73b4b8864f22d5e19dae0f155642cd > >> >> >> # timestamp: 2017-10-19 22:32:34 +0200 > >> >> >> # base_revision_id: [email protected]\ > >> >> >> # ndrkufle1quqodg8 > >> >> >> # > >> >> >> # Begin patch > >> >> >> === modified file 'uspace/lib/ext4/src/extent.c' > >> >> >> --- uspace/lib/ext4/src/extent.c 2017-05-11 22:07:09 +0000 > >> >> >> +++ uspace/lib/ext4/src/extent.c 2017-10-19 20:30:01 +0000 > >> >> >> @@ -374,7 +374,7 @@ > >> >> >> int ext4_extent_find_block(ext4_inode_ref_t *inode_ref, uint32_t > >> >> >> iblock, > >> >> >> uint32_t *fblock) > >> >> >> { > >> >> >> - int rc; > >> >> >> + int rc = EOK; > >> >> >> /* Compute bound defined by i-node size */ > >> >> >> uint64_t inode_size = > >> >> >> ext4_inode_get_size(inode_ref->fs->superblock, > >> >> >> inode_ref->inode); > >> >> >> > >> >> >> === modified file 'uspace/lib/trackmod/xm.c' > >> >> >> --- uspace/lib/trackmod/xm.c 2014-10-13 17:31:01 +0000 > >> >> >> +++ uspace/lib/trackmod/xm.c 2017-10-19 20:30:01 +0000 > >> >> >> @@ -288,7 +288,7 @@ > >> >> >> size_t samples; > >> >> >> size_t instr_size; > >> >> >> size_t smp_size; > >> >> >> - size_t smp_hdr_size; > >> >> >> + size_t smp_hdr_size = 0; /* GCC false alarm on uninitialized */ > >> >> >> ssize_t nread; > >> >> >> uint8_t ltype; > >> >> >> trackmod_sample_t *sample; > >> >> >> > >> >> >> # Begin bundle > >> >> >> IyBCYXphYXIgcmV2aXNpb24gYnVuZGxlIHY0CiMKQlpoOTFBWSZTWe8h8/IAAhpfrAAwUPf//17I > >> >> >> lAC////wACAAAgoAUASu73TT2tb13oim3qnhJQgp4m1T0mnqemTVPyp+o9Sfoo9qn6oMh6jQbRBl > >> >> >> GhGJpo0mkPU0A0AAAAABKEBRoyCbRMTT1GjQAAaNGgAaaoCbKNAAGjQaA0AGg0ABJJNGmpgTET0n > >> >> >> oENNI8pkaDQGgNGE5ypN3TW0+0R5HZU5WV9U0/YwFtIdsdkMEzXS50UmZKCSSkkO9B2beBJRTDBB > >> >> >> fETXzctT0PJvAt9bQk9U2VMYCzRs2vIqiyYKGc07734syjxSqw1mJBlQLfHZxNdkb7RszqhmPmzY > >> >> >> L+AbSq+tfe9BqrcUtO2E5Qwx5KxA6RX9ae6s2j4UjvnbmBv+Os3l0ewCIY0HDDAwyEwkwiQgTGkd > >> >> >> KppsRtJPGLIgqLCIPGf4Hd+wIEgyM41hteE6Rc3XdQUl7SltqQ4ZMpgvzIFuLoRaG/aXCyu7yFNq > >> >> >> EKwVI2HxRJwt7cSbcSIBfIUyLiwFZAzLDzWjgByvVSmxSDIDpMtldhLoyjaTq6dDxziYCQpNxcUA > >> >> >> UmyadFcQgM8Z7FprqSghIN+hLJSmhwAVsxF1ZCBRZcsz0BszFVp0V3idomXU0lZuwRhYSLg5lRbT > >> >> >> W7moCZEk9rTjBzCsXpFIt0BT6MD1DVZbXkFyiBWWCnyI54CE77CwZkiS11pEdNQSZ9rUQi5ixt7i > >> >> >> 64JiBZkBTqzC4Jg6TLDgFBZTAPaHSnVODxBYzGXDRyohYsvMQDPpKyV8nSMUH2OMlu5QxVezVOfk > >> >> >> esUalyPYFiraTEDjpdSVy1tQiCiFjKLLJQmGMRRoBdQOLBBJOzsPY1PqDbF8jGdJengFEu5nHMKP > >> >> >> qMpAM6leHOdcNhXTspYxNSYw+10EcO1dTVZMHrtxMY9/O9LSoU4INE9QQOOGNnFjaK3tget7SInN > >> >> >> hFFtpv6sEqdEmXGoi1DjkG8fSdheYa7pWaRVLPn2SIKw5mfxklL99FMvbWEwM8SlnW9XAX9pBdBP > >> >> >> CTGrcaJ5HvLTTl3vWgrAqphfE19OB3lZ2GM3Bh1haia+KDOdA/bncX4a37tDPd+kHOz3Qzsq5NMK > >> >> >> gYRJgaCNcF2Fd9p/ZALzoRjx8yPWbpRh0YHXcS9vdldGpiZcTeSFqvaSEpYsRWHtWOIErYBVHnLk > >> >> >> d50omtMjGwvR7xnjEm9wyrjQiRA7yh1mKrW0TzI8kPquqJX+f63Yw6UYIZBzRHMsvoPiQ8KfhJXo > >> >> >> nm4zwkKW2on1O9iYueSgChEjQpNc3OMLUwz8dK4w8C3g57O0DZ4LcruCthUY2ghjK4cZFH9pIacG > >> >> >> Q4CUEOVNfQ4ir74wNI0u3hBVDuZZf16C7erepZMURR2SnJFC63Kcz2gZfACtU6mGAWXai4Y9Tr0K > >> >> >> F2AcqItgRvWZXPJlttKHEhUeCwpFWVS1yoITAzidBNU/qjVQYOVJFGlA4PZQELCWmQgClk6RXJCP > >> >> >> zSKkCwKKItkBRz3m+QeRAzUxglsnxIgeF29VP4LNstLNyukyIpcZCySKtRjByqAgrj3nia6Dnjyb > >> >> >> MkajQmgcewDuAbNsVYiePp6YwfxdyRThQkO8h8/I > >> >> > > >> >> >> _______________________________________________ > >> >> >> HelenOS-devel mailing list > >> >> >> [email protected] > >> >> >> http://lists.modry.cz/listinfo/helenos-devel > >> >> > > >> >> > > >> >> > _______________________________________________ > >> >> > HelenOS-devel mailing list > >> >> > [email protected] > >> >> > http://lists.modry.cz/listinfo/helenos-devel > >> >> > >> >> _______________________________________________ > >> >> HelenOS-devel mailing list > >> >> [email protected] > >> >> http://lists.modry.cz/listinfo/helenos-devel > >> > > >> > _______________________________________________ > >> > HelenOS-devel mailing list > >> > [email protected] > >> > http://lists.modry.cz/listinfo/helenos-devel > >> > >> _______________________________________________ > >> HelenOS-devel mailing list > >> [email protected] > >> http://lists.modry.cz/listinfo/helenos-devel > > > > _______________________________________________ > > HelenOS-devel mailing list > > [email protected] > > http://lists.modry.cz/listinfo/helenos-devel > > _______________________________________________ > HelenOS-devel mailing list > [email protected] > http://lists.modry.cz/listinfo/helenos-devel _______________________________________________ HelenOS-devel mailing list [email protected] http://lists.modry.cz/listinfo/helenos-devel
