[Fixed linux-arm-kernel mailing list address, sorry for the duplicate, I'm not reposting all the ugly patches though, unless someone really wants them, https://lkml.org/lkml/2016/12/16/174 has a copy] On Friday, December 16, 2016 11:56:21 AM CET Arnd Bergmann wrote: > I had some fun doing build testing with older gcc versions, building > every release from 4.0 through 7.0 and running that on my randconfig > setup to see what comes out. > > First of all, gcc-4.9 and higher is basically warning-free everywhere, > although gcc-7 introduces some interesting new warnings (I have started > doing patches for those as well). gcc-4.8 is probably good, too, and > gcc-4.6 and 4.7 at least don't produce build failures in general, though > the level of false-positive warnings increases (we could decide to turn > those off for older compilers for build test purposes). > > In gcc-4.5 and below, dead code elimination is not as good as later, > causing a couple of link errors, and some of them have no good workaround > (see patch 1). It would be nice to declare that version too old, but > several older distros that are still in wide use ship with compilers > earlier than 4.6: > > RHEL6: gcc-4.4 > Debian 6: gcc-4.4 > Ubuntu 10.04: gcc-4.4 > SLES11: gcc-4.3 > > With gcc-4.3, we need a couple of workaround patches beyond the problem > mentioned above, more configuration options are unavailable and we get > a significant number of false-positive warnings, but it's not much worse > than gcc-4.5 otherwise. > > These are the options I had to disable to get gcc-4.3 randconfig builds > working: > > CONFIG_HAVE_GCC_PLUGINS > CONFIG_CC_STACKPROTECTOR_STRONG > CONFIG_ARM_SINGLE_ARMV7M > CONFIG_THUMB2_KERNEL > CONFIG_KERNEL_MODE_NEON > CONFIG_VDSO > CONFIG_FUNCTION_TRACER (with CONFIG_FRAME_POINTER=n) > > I have not checked in detail which version is required for > each of the above. > > Specifically on ARM, going further makes things rather useless especially > for build testing: with gcc-4.2, we lose support for ARMv7, EABI, and > effectively ARMv6 (as it relies on EABI for building reliably). Also, > the number of false-positive build warnings is so high that it is useless > for finding actual bugs from the warnings. > > See the replies to this mail for 13 patches I needed to work around > issues for each of the releases before 4.6. I have also submitted > some separate patches for issues that I considered actual bugs > uncovered by the older compilers and that should be applied regardless. > > The original gcc-4.3 release was in early 2008. If we decide to still > support that, we probably want the first 10 quirks in this series, > while gcc-4.6 (released in 2011) requires none of them. > > Arnd > > Arnd Bergmann (13): > [HACK] gcc-4.5: avoid link errors for unused function pointers > KVM: arm: fix gcc-4.5 build > ARM: div64: fix building with gcc-4.5 and lower > vfio-pci: use 32-bit comparisons for register address for gcc-4.5 > clk: pxa: fix gcc-4.4 build > ARM: atomic: fix gcc-4.4 build > watchdog: kempld: fix gcc-4.3 build > arm/arm64: xen: avoid gcc-4.4 warning > ARM: mark cmpxchg and xchg __always_inline for gcc-4.3 > asm-generic: mark cmpxchg as __always_inline for gcc-4.3 > fs: fix unsigned enum warning with gcc-4.2 > KVM: arm: avoid binary number literals for gcc-4.2 > ARM: avoid 'Q' asm constraint for gcc-4.1 and earlier > > arch/arm/include/asm/atomic.h | 10 ++++++++-- > arch/arm/include/asm/cmpxchg.h | 12 ++++++------ > arch/arm/include/asm/div64.h | 17 +++-------------- > arch/arm/include/asm/io.h | 8 ++++++++ > arch/arm/include/asm/kvm_mmu.h | 2 +- > arch/arm/include/asm/percpu.h | 5 ++++- > arch/arm/mach-imx/pm-imx5.c | 20 ++++++++++++++++---- > arch/arm/mach-sa1100/pm.c | 2 ++ > arch/arm/plat-samsung/pm.c | 4 ++++ > drivers/clk/pxa/clk-pxa.c | 3 +-- > drivers/dma/ti-dma-crossbar.c | 4 ++++ > drivers/firmware/psci_checker.c | 3 +++ > drivers/iio/adc/exynos_adc.c | 3 +++ > drivers/net/ethernet/via/via-rhine.c | 6 ++++++ > drivers/vfio/pci/vfio_pci_rdwr.c | 5 ++++- > drivers/watchdog/kempld_wdt.c | 9 ++++++++- > include/asm-generic/cmpxchg-local.h | 7 ++++--- > include/linux/fs.h | 2 +- > include/xen/arm/page.h | 1 + > virt/kvm/arm/vgic/vgic-its.c | 4 ++-- > virt/kvm/arm/vgic/vgic-mmio-v3.c | 8 ++++---- > virt/kvm/arm/vgic/vgic-mmio.c | 16 ++++++++-------- > virt/kvm/arm/vgic/vgic-mmio.h | 12 ++++++------ > 23 files changed, 107 insertions(+), 56 deletions(-) > > -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
