From 47c5adebd2c864a098c3af66e61e1147dc3cf0b4 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Mon, 31 Mar 2014 12:55:18 +0000 Subject: Correct robust mutex / PI futex kernel assumptions (bug 9894). This patch continues fixing __ASSUME_* issues in preparation for moving to a 2.6.32 minimum kernel version by addressing assumptions on robust mutex and PI futex support availability. Those assumptions are bug 9894, but to be clear this patch does not address all the issues from that bug about wrong version assumptions, only those still applicable for --enable-kernel=2.6.32 or later (with the expectation that the move to that minimum kernel will obsolete the other parts of the bug). The patch is independent of , my other pending-review patch preparing for the kernel version change; the two together complete all the changes I believe are needed in preparation regarding any macro in sysdeps/unix/sysv/linux/kernel-features.h that would be affected by such a change. (I have not checked the correctness of macros whose conditions are unaffected by such a change, or macros only defined in other kernel-features.h files.) As discussed in that bug, robust mutexes and PI futexes need futex_atomic_cmpxchg_inatomic to be implemented, in addition to certain syscalls needed for robust mutexes (and architecture-independent kernel pieces for all the features in question). That is, as I understand it, they need futex_atomic_cmpxchg_inatomic to *work* (not return an ENOSYS error). The issues identified in my analysis relate to ARM, M68K, MicroBlaze, MIPS and SPARC. On ARM, whether futex_atomic_cmpxchg_inatomic works depends on the kernel configuration. As of 3.13, the condition for *not* working is CONFIG_CPU_USE_DOMAINS && CONFIG_SMP. As of 2.6.32 it was simply CONFIG_SMP that meant the feature was not implemented. I don't know if there are any circumstances in which we can say "we can assume a userspace glibc binary built with these options will never run on a kernel with the problematic configuration", but at least for now I'm just undefining the relevant __ASSUME_* macros for ARM. On M68K, two of the three macros are undefined for kernels before 3.10, but as far as I can see __ASSUME_FUTEX_LOCK_PI is in the same group needing futex_atomic_cmpxchg_inatomic support and so should be undefined as well. On MicroBlaze the required support was added in 2.6.33. On MIPS, the support depends on cpu_has_llsc in the kernel - that is, actual hardware LL/SC support (GCC and glibc for MIPS GNU/Linux rely on the instructions being supported in some way, but it may be kernel emulation; futex_atomic_cmpxchg_inatomic doesn't work with that emulation). The same condition as in GCC for indicating LL/SC support may not be available is used for undefining the macros in glibc, __mips == 1 || defined _MIPS_ARCH_R5900. (Maybe we could in fact desupport MIPS processors without the hardware support in glibc.) On SPARC, 32-bit kernels don't support futex_atomic_cmpxchg_inatomic; __arch64__ || __sparc_v9__ is used as the condition for binaries that won't run on 32-bit kernels. This patch is not tested beyond the sanity check of an x86_64 build. [BZ #9894] * sysdeps/unix/sysv/linux/kernel-features.h [__sparc__ && !__arch64__ && !__sparc_v9__] (__ASSUME_SET_ROBUST_LIST): Do not define. [__sparc__ && !__arch64__ && !__sparc_v9__] (__ASSUME_FUTEX_LOCK_PI): Likewise. [__sparc__ && !__arch64__ && !__sparc_v9__] (__ASSUME_REQUEUE_PI): Likewise. * sysdeps/unix/sysv/linux/arm/kernel-features.h (__ASSUME_FUTEX_LOCK_PI): Undefine. (__ASSUME_REQUEUE_PI): Likewise. (__ASSUME_SET_ROBUST_LIST): Likewise. * sysdeps/unix/sysv/linux/m68k/kernel-features.h [__LINUX_KERNEL_VERSION < 0x030a00] (__ASSUME_FUTEX_LOCK_PI): Undefine. * sysdeps/unix/sysv/linux/microblaze/kernel-features.h [__LINUX_KERNEL_VERSION < 0x020621] (__ASSUME_FUTEX_LOCK_PI): Likewise. [__LINUX_KERNEL_VERSION < 0x020621] (__ASSUME_REQUEUE_PI): Likewise. [__LINUX_KERNEL_VERSION < 0x020621] (__ASSUME_SET_ROBUST_LIST): Likewise. * sysdeps/unix/sysv/linux/mips/kernel-features.h [__mips == 1 || _MIPS_ARCH_R5900] (__ASSUME_FUTEX_LOCK_PI): Undefine. [__mips == 1 || _MIPS_ARCH_R5900] (__ASSUME_REQUEUE_PI): Likewise. [__mips == 1 || _MIPS_ARCH_R5900] (__ASSUME_SET_ROBUST_LIST): Likewise. --- sysdeps/unix/sysv/linux/mips/kernel-features.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'sysdeps/unix/sysv/linux/mips') diff --git a/sysdeps/unix/sysv/linux/mips/kernel-features.h b/sysdeps/unix/sysv/linux/mips/kernel-features.h index 52cbf3a5ba..19d3cba1b0 100644 --- a/sysdeps/unix/sysv/linux/mips/kernel-features.h +++ b/sysdeps/unix/sysv/linux/mips/kernel-features.h @@ -53,3 +53,11 @@ #if _MIPS_SIM == _ABIN32 && __LINUX_KERNEL_VERSION < 0x020623 # undef __ASSUME_GETDENTS64_SYSCALL #endif + +/* The MIPS kernel does not support futex_atomic_cmpxchg_inatomic if + emulating LL/SC. */ +#if __mips == 1 || defined _MIPS_ARCH_R5900 +# undef __ASSUME_FUTEX_LOCK_PI +# undef __ASSUME_REQUEUE_PI +# undef __ASSUME_SET_ROBUST_LIST +#endif -- cgit 1.4.1