- 21 Apr, 2020 2 commits
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Michael Ellerman authored
As described by Haren: Power9 processor supports Virtual Accelerator Switchboard (VAS) which allows kernel and userspace to send compression requests to Nest Accelerator (NX) directly. The NX unit comprises of 2 842 compression engines and 1 GZIP engine. Linux kernel already has 842 compression support on kernel. This patch series adds GZIP compression support from user space. The GZIP Compression engine implements the ZLIB and GZIP compression algorithms. No plans of adding NX-GZIP compression support in kernel right now. Applications can send requests to NX directly with COPY/PASTE instructions. But kernel has to establish channel / window on NX-GZIP device for the userspace. So userspace access to the GZIP engine is provided through /dev/crypto/nx-gzip device with several operations. An application must open the this device to obtain a file descriptor (fd). Using the fd, application should issue the VAS_TX_WIN_OPEN ioctl to establish a connection to the engine. Once window is opened, should use mmap() system call to map the hardware address of engine's request queue into the application's virtual address space. Then user space forms the request as co-processor Request Block (CRB) and paste this CRB on the mapped HW address using COPY/PASTE instructions. Application can poll on status flags (part of CRB) with timeout for request completion. For VAS_TX_WIN_OPEN ioctl, if user space passes vas_id = -1 (struct vas_tx_win_open_attr), kernel determines the VAS instance on the corresponding chip based on the CPU on which the process is executing. Otherwise, the specified VAS instance is used if application passes the proper VAS instance (vas_id listed in /proc/device-tree/vas@*/ibm,vas_id). Process can open multiple windows with different FDs or can send several requests to NX on the same window at the same time.
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Michael Ellerman authored
As described by Haren: On Power9, Virtual Accelerator Switchboard (VAS) allows user space or kernel to communicate with Nest Accelerator (NX) directly using COPY/PASTE instructions. NX provides various functionalities such as compression, encryption and etc. But only compression (842 and GZIP formats) is supported in Linux kernel on power9. 842 compression driver (drivers/crypto/nx/nx-842-powernv.c) is already included in Linux. Only GZIP support will be available from user space. Applications can issue GZIP compression / decompression requests to NX with COPY/PASTE instructions. When NX is processing these requests, can hit fault on the request buffer (not in memory). It issues an interrupt and pastes fault CRB in fault FIFO. Expects kernel to handle this fault and return credits for both send and fault windows after processing. This patch series adds IRQ and fault window setup, and NX fault handling: - Alloc IRQ and trigger port address, and configure IRQ per VAS instance. - Set port# for each window to generate an interrupt when noticed fault. - Set fault window and FIFO on which NX paste fault CRB. - Setup IRQ thread fault handler per VAS instance. - When receiving an interrupt, Read CRBs from fault FIFO and update coprocessor_status_block (CSB) in the corresponding CRB with translation failure (CSB_CC_TRANSLATION). After issuing NX requests, process polls on CSB address. When it sees translation error, can touch the request buffer to bring the page in to memory and reissue NX request. - If copy_to_user fails on user space CSB address, OS sends SEGV signal.
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- 20 Apr, 2020 23 commits
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Haren Myneni authored
Power9 introduced Virtual Accelerator Switchboard (VAS) which allows userspace to communicate with Nest Accelerator (NX) directly. But kernel has to establish channel to NX for userspace. This document describes user space API that application can use to establish communication channel. Signed-off-by:
Sukadev Bhattiprolu <sukadev@linux.ibm.com> Signed-off-by:
Haren Myneni <haren@linux.ibm.com> Signed-off-by:
Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/1587114715.2275.1135.camel@hbabu-laptop
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Haren Myneni authored
When window is opened, pid reference is taken for user space windows. Not needed for kernel windows. So remove 'pid' in vas_tx_win_attr struct. Signed-off-by:
Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by:
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Haren Myneni authored
Changes to probe GZIP device-tree nodes, open RX windows and setup GZIP compression type. No plans to provide GZIP usage in kernel right now, but this patch enables GZIP for user space usage. Signed-off-by:
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Haren Myneni authored
Make setup and enable code generic to support new GZIP compression type. Changed nx842 reference to nx and moved some code to new functions. Functionality is not changed except sparse warning fix - setting NULL instead of 0 for per_cpu send window in nx_delete_coprocs(). Signed-off-by:
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Haren Myneni authored
Rename nx-842-powernv.c to nx-common-powernv.c to add code for setup and enable new GZIP compression type. The actual functionality is not changed in this patch. Signed-off-by:
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Haren Myneni authored
coproc entry is initialized during NX probe on power9, but not on P8. nx842_delete_coprocs() is used for both and frees receive window if it is allocated. Getting crash for rmmod on P8 since coproc->vas.rxwin is not initialized. This patch replaces kmalloc with kzalloc in nx842_powernv_probe() Signed-off-by:
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Haren Myneni authored
On power9, userspace can send GZIP compression requests directly to NX once kernel establishes NX channel / window with VAS. This patch provides user space API which allows user space to establish channel using open VAS_TX_WIN_OPEN ioctl, mmap and close operations. Each window corresponds to file descriptor and application can open multiple windows. After the window is opened, VAS_TX_WIN_OPEN icoctl to open a window on specific VAS instance, mmap() system call to map the hardware address of engine's request queue into the application's virtual address space. Then the application can then submit one or more requests to the the engine by using the copy/paste instructions and pasting the CRBs to the virtual address (aka paste_address) returned by mmap(). Only NX GZIP coprocessor type is supported right now and allow GZIP engine access via /dev/crypto/nx-gzip device node. Thanks to Michael Ellerman for his changes and suggestions to make the ioctl generic to support any coprocessor type. Signed-off-by:
Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> Signed-off-by:
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Haren Myneni authored
Define the VAS_TX_WIN_OPEN ioctl interface for NX GZIP access from user space. This interface is used to open GZIP send window and mmap region which can be used by userspace to send requests to NX directly with copy/paste instructions. Signed-off-by:
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Haren Myneni authored
Initialize send and receive window attributes for GZIP high and normal priority types. Signed-off-by:
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Haren Myneni authored
set_thread_uses_vas() sets used_vas flag for a process that opened VAS window and issue CP_ABORT during context switch for only that process. In multi-thread application, windows can be shared. For example Thread A can open a window and Thread B can run COPY/PASTE instructions to send NX request which may cause corruption or snooping or a covert channel Also once this flag is set, continue to run CP_ABORT even the VAS window is closed. So define vas-windows counter in process mm_context, increment this counter for each window open and decrement it for window close. If vas-windows is set, issue CP_ABORT during context switch. It means clear the foreign real address mapping only if the process / thread uses COPY/PASTE. Then disable it for that process if windows are not open. Moved set_thread_uses_vas() code to vas_tx_win_open() as this functionality is needed only for userspace open windows. We are adding VAS userspace support along with this fix. So no need to include this fix in stable releases. Fixes: 9d2a4d71 ("powerpc: Define set_thread_uses_vas()") Signed-off-by:
Nicholas Piggin <npiggin@gmail.com> Suggested-by:
Milton Miller <miltonm@us.ibm.com> Suggested-by:
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Haren Myneni authored
NX may be processing requests while trying to close window. Wait until all credits are returned and then free send window from VAS instance. Signed-off-by:
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Haren Myneni authored
Process can not close send window until all requests are processed. Means wait until window state is not busy and send credits are returned. Display debug messages in case taking longer to close the window. Signed-off-by:
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Haren Myneni authored
System checkstops if RxFIFO overruns with more requests than the maximum possible number of CRBs allowed in FIFO at any time. So max credits value (rxattr.wcreds_max) is set and is passed to vas_rx_win_open() by the the driver. Signed-off-by:
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Haren Myneni authored
Dump FIFO entries if could not find send window and print CRB for debugging. Signed-off-by:
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Haren Myneni authored
NX uses credit mechanism to control the number of requests issued on a specific window at any point of time. Only send windows and fault window are used credits. When the request is issued on a given window, a credit is taken. This credit will be returned after that request is processed. If credits are not available, returns RMA_Busy for send window and RMA_Reject for fault window. NX expects OS to return credit for send window after processing fault CRB. Also credit has to be returned for fault window after handling the fault. Signed-off-by:
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Haren Myneni authored
Applications polls on CSB for the status update after requests are issued. NX process these requests and update the CSB with the status. If it encounters translation error, pastes CRB in fault FIFO and raises an interrupt. The kernel handles fault by reading CRB from fault FIFO and process the fault CRB. For each fault CRB, update fault address in CRB (fault_storage_addr) and translation error status in CSB so that user space can touch the fault address and resend the request. If the user space passed invalid CSB address send signal to process with SIGSEGV. In the case of multi-thread applications, child thread may not be available. So if the task is not running, send signal to tgid. Signed-off-by:
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Haren Myneni authored
When NX encounters translation error on CRB and any request buffer, raises an interrupt on the CPU to handle the fault. It can raise one interrupt for multiple faults. Expects OS to handle these faults and return credits for fault window after processing faults. Setup thread IRQ handler and IRQ thread function per each VAS instance. IRQ handler checks if the thread is already woken up and can handle new faults. If so returns with IRQ_HANDLED, otherwise wake up thread to process new faults. The thread functions reads each CRB entry from fault FIFO until sees invalid entry. After reading each CRB, determine the corresponding send window using pswid (from CRB) and process fault CRB. Then invalidate the entry and return credit. Processing fault CRB and return credit is described in subsequent patches. Signed-off-by:
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Haren Myneni authored
When process opens a window, its pid and tgid will be saved in the vas_window struct. This window will be closed when the process exits. The kernel handles NX faults by updating CSB or send SEGV signal to pid of the process if the userspace csb addr is invalid. In multi-thread applications, a window can be opened by a child thread, but it will not be closed when this thread exits. It is expected that the parent will clean up all resources including NX windows opened by child threads. A child thread can send NX requests using this window and could be killed before completion is reported. If the pid assigned to this thread is reused while requests are pending, a failure SEGV would be directed to the wrong place. To prevent reusing the pid, take references to pid and mm when the window is opened and release them when when the window is closed. Then if child thread is not running, SEGV signal will be sent to thread group leader (tgid). Signed-off-by:
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Haren Myneni authored
For each user space send window, register NX with fault window ID and port value so that NX paste CRBs in this fault FIFO when it sees fault on the request buffer. Signed-off-by:
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Haren Myneni authored
Setup fault window for each VAS instance. When NX gets a fault on request buffer, pastes fault CRB in the corresponding fault FIFO and then raises an interrupt to the OS. The kernel handles this fault and process faults CRB from this FIFO. Signed-off-by:
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Haren Myneni authored
Allocate a xive irq on each chip with a vas instance. The NX coprocessor raises a host CPU interrupt via vas if it encounters page fault on user space request buffer. Subsequent patches register the trigger port with the NX coprocessor, and create a vas fault handler for this interrupt mapping. Signed-off-by:
Cédric Le Goater <clg@kaod.org> Signed-off-by:
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Haren Myneni authored
Kernel sets fault address and status in CRB for NX page fault on user space address after processing page fault. User space gets the signal and handles the fault mentioned in CRB by bringing the page in to memory and send NX request again. Signed-off-by:
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Haren Myneni authored
This function allocates IRQ on a specific chip. VAS needs per chip IRQ allocation and will have IRQ handler per VAS instance. Signed-off-by:
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- 19 Apr, 2020 12 commits
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Linus Torvalds authored
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Brian Geffon authored
When remapping a mapping where a portion of a VMA is remapped into another portion of the VMA it can cause the VMA to become split. During the copy_vma operation the VMA can actually be remerged if it's an anonymous VMA whose pages have not yet been faulted. This isn't normally a problem because at the end of the remap the original portion is unmapped causing it to become split again. However, MREMAP_DONTUNMAP leaves that original portion in place which means that the VMA which was split and then remerged is not actually split at the end of the mremap. This patch fixes a bug where we don't detect that the VMAs got remerged and we end up putting back VM_ACCOUNT on the next mapping which is completely unreleated. When that next mapping is unmapped it results in incorrectly unaccounting for the memory which was never accounted, and eventually we will underflow on the memory comittment. There is also another issue which is similar, we're currently accouting for the number of pages in the new_vma but that's wrong. We need to account for the length of the remap operation as that's all that is being added. If there was a mapping already at that location its comittment would have been adjusted as part of the munmap at the start of the mremap. A really simple repro can be seen in: https://gist.github.com/bgaff/e101ce99da7d9a8c60acc641d07f312c Fixes: e346b381 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()") Reported-by:
syzbot <syzkaller@googlegroups.com> Signed-off-by:
Brian Geffon <bgeffon@google.com> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/clk/linuxLinus Torvalds authored
Pull clk fixes from Stephen Boyd: "Two build fixes for a couple clk drivers and a fix for the Unisoc serial clk where we want to keep it on for earlycon" * tag 'clk-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux: clk: sprd: don't gate uart console clock clk: mmp2: fix link error without mmp2 clk: asm9260: fix __clk_hw_register_fixed_rate_with_accuracy typo
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull x86 and objtool fixes from Thomas Gleixner: "A set of fixes for x86 and objtool: objtool: - Ignore the double UD2 which is emitted in BUG() when CONFIG_UBSAN_TRAP is enabled. - Support clang non-section symbols in objtool ORC dump - Fix switch table detection in .text.unlikely - Make the BP scratch register warning more robust. x86: - Increase microcode maximum patch size for AMD to cope with new CPUs which have a larger patch size. - Fix a crash in the resource control filesystem when the removal of the default resource group is attempted. - Preserve Code and Data Prioritization enabled state accross CPU hotplug. - Update split lock cpu matching to use the new X86_MATCH macros. - Change the split lock enumeration as Intel finaly decided that the IA32_CORE_CAPABILITIES bits are not architectural contrary to what the SDM claims. !@#%$^! - Add Tremont CPU models to the split lock detection cpu match. - Add a missing static attribute to make sparse happy" * tag 'x86-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/split_lock: Add Tremont family CPU models x86/split_lock: Bits in IA32_CORE_CAPABILITIES are not architectural x86/resctrl: Preserve CDP enable over CPU hotplug x86/resctrl: Fix invalid attempt at removing the default resource group x86/split_lock: Update to use X86_MATCH_INTEL_FAM6_MODEL() x86/umip: Make umip_insns static x86/microcode/AMD: Increase microcode PATCH_MAX_SIZE objtool: Make BP scratch register warning more robust objtool: Fix switch table detection in .text.unlikely objtool: Support Clang non-section symbols in ORC generation objtool: Support Clang non-section symbols in ORC dump objtool: Fix CONFIG_UBSAN_TRAP unreachable warnings -
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull time namespace fix from Thomas Gleixner: "An update for the proc interface of time namespaces: Use symbolic names instead of clockid numbers. The usability nuisance of numbers was noticed by Michael when polishing the man page" * tag 'timers-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: proc, time/namespace: Show clock symbolic names in /proc/pid/timens_offsets
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull perf tooling fixes and updates from Thomas Gleixner: - Fix the header line of perf stat output for '--metric-only --per-socket' - Fix the python build with clang - The usual tools UAPI header synchronization * tag 'perf-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: tools headers: Synchronize linux/bits.h with the kernel sources tools headers: Adopt verbatim copy of compiletime_assert() from kernel sources tools headers: Update x86's syscall_64.tbl with the kernel sources tools headers UAPI: Sync drm/i915_drm.h with the kernel sources tools headers UAPI: Update tools's copy of drm.h headers tools headers kvm: Sync linux/kvm.h with the kernel sources tools headers UAPI: Sync linux/fscrypt.h with the kernel sources tools include UAPI: Sync linux/vhost.h with the kernel sources tools arch x86: Sync asm/cpufeatures.h with the kernel sources tools headers UAPI: Sync linux/mman.h with the kernel tools headers UAPI: Sync sched.h with the kernel tools headers: Update linux/vdso.h and grab a copy of vdso/const.h perf stat: Fix no metric header if --per-socket and --metric-only set perf python: Check if clang supports -fno-semantic-interposition tools arch x86: Sync the msr-index.h copy with the kernel sources
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull irq fixes from Thomas Gleixner: "A set of fixes/updates for the interrupt subsystem: - Remove setup_irq() and remove_irq(). All users have been converted so remove them before new users surface. - A set of bugfixes for various interrupt chip drivers - Add a few missing static attributes to address sparse warnings" * tag 'irq-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: irqchip/irq-bcm7038-l1: Make bcm7038_l1_of_init() static irqchip/irq-mvebu-icu: Make legacy_bindings static irqchip/meson-gpio: Fix HARDIRQ-safe -> HARDIRQ-unsafe lock order irqchip/sifive-plic: Fix maximum priority threshold value irqchip/ti-sci-inta: Fix processing of masked irqs irqchip/mbigen: Free msi_desc on device teardown irqchip/gic-v4.1: Update effective affinity of virtual SGIs irqchip/gic-v4.1: Add support for VPENDBASER's Dirty+Valid signaling genirq: Remove setup_irq() and remove_irq() -
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull scheduler fixes from Thomas Gleixner: "Two fixes for the scheduler: - Work around an uninitialized variable warning where GCC can't figure it out. - Allow 'isolcpus=' to skip unknown subparameters so that older kernels work with the commandline of a newer kernel. Improve the error output while at it" * tag 'sched-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: sched/vtime: Work around an unitialized variable warning sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters -
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipLinus Torvalds authored
Pull RCU fix from Thomas Gleixner: "A single bugfix for RCU to prevent taking a lock in NMI context" * tag 'core-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common()
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git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4Linus Torvalds authored
Pull ext4 fixes from Ted Ts'o: "Miscellaneous bug fixes and cleanups for ext4, including a fix for generic/388 in data=journal mode, removing some BUG_ON's, and cleaning up some compiler warnings" * tag 'ext4_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4: ext4: convert BUG_ON's to WARN_ON's in mballoc.c ext4: increase wait time needed before reuse of deleted inode numbers ext4: remove set but not used variable 'es' in ext4_jbd2.c ext4: remove set but not used variable 'es' ext4: do not zeroout extents beyond i_disksize ext4: fix return-value types in several function comments ext4: use non-movable memory for superblock readahead ext4: use matching invalidatepage in ext4_writepage
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git://git.samba.org/sfrench/cifs-2.6Linus Torvalds authored
Pull cifs fixes from Steve French: "Three small smb3 fixes: two debug related (helping network tracing for SMB2 mounts, and the other removing an unintended debug line on signing failures), and one fixing a performance problem with 64K pages" * tag '5.7-rc-smb3-fixes' of git://git.samba.org/sfrench/cifs-2.6: smb3: remove overly noisy debug line in signing errors cifs: improve read performance for page size 64KB & cache=strict & vers=2.1+ cifs: dump the session id and keys also for SMB2 sessions
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Linus Torvalds authored
Merge tag 'flexible-array-member-5.7-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux Pull flexible-array member conversion from Gustavo Silva: "The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member convertions) will also help to get completely rid of those sorts of issues. Notice that all of these patches have been baking in linux-next for quite a while now and, 238 more of these patches have already been merged into 5.7-rc1. There are a couple hundred more of these issues waiting to be addressed in the whole codebase" [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour") * tag 'flexible-array-member-5.7-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux: (28 commits) xattr.h: Replace zero-length array with flexible-array member uapi: linux: fiemap.h: Replace zero-length array with flexible-array member uapi: linux: dlm_device.h: Replace zero-length array with flexible-array member tpm_eventlog.h: Replace zero-length array with flexible-array member ti_wilink_st.h: Replace zero-length array with flexible-array member swap.h: Replace zero-length array with flexible-array member skbuff.h: Replace zero-length array with flexible-array member sched: topology.h: Replace zero-length array with flexible-array member rslib.h: Replace zero-length array with flexible-array member rio.h: Replace zero-length array with flexible-array member posix_acl.h: Replace zero-length array with flexible-array member platform_data: wilco-ec.h: Replace zero-length array with flexible-array member memcontrol.h: Replace zero-length array with flexible-array member list_lru.h: Replace zero-length array with flexible-array member lib: cpu_rmap: Replace zero-length array with flexible-array member irq.h: Replace zero-length array with flexible-array member ihex.h: Replace zero-length array with flexible-array member igmp.h: Replace zero-length array with flexible-array member genalloc.h: Replace zero-length array with flexible-array member ethtool.h: Replace zero-length array with flexible-array member ...
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- 18 Apr, 2020 3 commits
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git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsiLinus Torvalds authored
Pull SCSI fixes from James Bottomley: "Seven fixes: three in target, one on a sg error leg, two in qla2xxx fixing warnings introduced in the last merge window and updating MAINTAINERS and one in hisi_sas fixing a problem introduced by libata" * tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi: scsi: sg: add sg_remove_request in sg_common_write scsi: target: tcmu: reset_ring should reset TCMU_DEV_BIT_BROKEN scsi: target: fix PR IN / READ FULL STATUS for FC scsi: target: Write NULL to *port_nexus_ptr if no ISID scsi: MAINTAINERS: Update qla2xxx FC-SCSI driver maintainer scsi: qla2xxx: Fix regression warnings scsi: hisi_sas: Fix build error without SATA_HOST
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Gustavo A. R. Silva authored
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by:Gustavo A. R. Silva <gustavo@embeddedor.com>
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Gustavo A. R. Silva authored
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by:
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