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[Minios-devel] [UNIKRAFT PATCH v4 0/7] Thread-local storage support

From: Florian Schmidt <florian.schmidt@xxxxxxxxx>

Date: Sun, 2 Jun 2019 07:02:29 +0100

Cc: Florian Schmidt <florian.schmidt@xxxxxxxxx>, Costin Lupu <costin.lupu@xxxxxxxxx>

Delivery-date: Sun, 02 Jun 2019 06:03:00 +0000

List-id: Mini-os development list <minios-devel.lists.xenproject.org>

This is v4 of the TLS series that allows the use of __thread variables. The changes are minimal, just a small change in patch 1 to make it apply cleanly to staging again, and a typo fix in patch 2. *** v3 text below for reference *** This is v3 of the TLS series that allows the use of __thread variables. The main changes from v2 are: * Added a patch (1/7) that makes the plat/linuxu linker script preprocessable. Used that to use the same macros in that linker script as in the kvm and Xen ones. * Fixed indentation. * Moved a copyright notice. *** v2 text below for reference *** This is v2 of the TLS series that allows the use of __thread variables. I reordered and refactored the patches quite extensively in the hopes of making them more easy to follow and fix potential breaking of compiles. The main changes from v1 are: * Unifying the TLS section entries for the linker script by adding them to common.lds.h that was added in patch e6a88d61. * The first two patches aren't directly related to the series, but likewise leverage e6a88d61 for further linker script unification and replacement of numbers with defines. * The implementation of the architecture-dependent helper functions is now done both for x86 and for the Arm stub versions in one patch, and before any of the functionality is used in plat/ code. That fixes a problem with builds breaking for Arm before the last patch in the series. * Renamed several header files to tls.h. I could still imagine those being of more general use in the future (e.g., putting the extended register switching code in there), but we can always rename them if and when that happens. *** v1 text below for reference *** This patch series introduces so-called "native" thread-local storage support to unikraft. That is, static variables can be annotated with the keyword '__thread' and then work as thread-local variables. That is, a global or static local variable '__thread int a' will be thread-specific, without any need for other syntactic hoops to jump through (why hello there, pthread keys!). This works by aggregating all these variables into two specific ELF sections, .tdata and .tbss, depending on whether they are initialized at compile time or not. Each thread, on creation, then gets a copy of this area. A register is then set aside to point at this area, allowing immediate and efficient access by just reading from and writing to addresses defined by an offset from the address the register contains. When switching between threads, the register's content is changed to point to the corresponding TLS area. For unikraft, I only implemented this simple implementation. All of this gets a lot more complicated when dynamic linking is added to the mix, requiring relocation, lookup vectors, etc. Thankfully, for a unikernel, none of this matters really... unless someone wants to implement dynamic linking for unikraft, then they'll have to revisit this. Room for improvement: 1) The Arm implementation is by no stretch of imagination complete. There's only boilerplate code for creating the TLS area, and none at all for TLS register switching at context switch. This is mostly because there is, as of yet, no proper scheduling support for Arm, so this will have to be revisited at that point. I tried to set everything up to make adding this feature as painless as possible. 2) The current implementation always mallocs a new area for each thread's TLS. This could be optimized by reducing the number of mallocs. For example, the TLS area could be allocated in one contiguous block with the uk_thread structure or the stack, or, if the TLS area is small, it could be directly allocated on the thread's stack. Florian Schmidt (7): plat/linuxu: make linker script preprocessable plat: move common section definitions from linker script to include file plat: Replace 0x1000 / 4096 with __PAGE_SIZE plat: prepare linker script for thread-local storage arch: provide thread-local storage helper functions lib/uksched: create and delete thread-local storage area plat: switch thread-local storage area on context switch arch/arm/arm/include/uk/asm/tls.h | 62 ++++++++++++++++ arch/arm/arm64/include/uk/asm/tls.h | 72 ++++++++++++++++++ arch/x86/x86_64/include/uk/asm/tls.h | 73 +++++++++++++++++++ include/uk/arch/tls.h | 40 ++++++++++ include/uk/plat/thread.h | 8 +- lib/uksched/include/uk/sched.h | 3 + lib/uksched/include/uk/thread.h | 3 +- lib/uksched/sched.c | 35 ++++++++- lib/uksched/thread.c | 13 ++-- plat/common/include/common.lds.h | 51 ++++++++++++- plat/common/include/sections.h | 5 ++ plat/common/include/sw_ctx.h | 1 + plat/common/include/tls.h | 41 +++++++++++ plat/common/include/x86/cpu_defs.h | 5 ++ plat/common/include/x86/tls.h | 39 ++++++++++ plat/common/sw_ctx.c | 10 ++- plat/kvm/arm/link64.lds.S | 30 +------- plat/kvm/x86/link64.lds.S | 15 ++-- plat/linuxu/Linker.uk | 8 +- plat/linuxu/Makefile.uk | 4 + plat/linuxu/arm/link.lds | 11 --- plat/linuxu/arm/link.lds.S | 7 ++ plat/linuxu/include/linuxu/syscall-x86_64.h | 1 + plat/linuxu/include/linuxu/syscall.h | 8 ++ .../x86/link64.lds => linuxu/include/tls.h} | 31 ++------ plat/linuxu/x86/link64.lds | 6 -- plat/linuxu/x86/link64.lds.S | 16 ++++ plat/xen/arm/link32.lds.S | 37 ++-------- plat/xen/x86/link64.lds.S | 13 +++- 29 files changed, 523 insertions(+), 125 deletions(-) create mode 100644 arch/arm/arm/include/uk/asm/tls.h create mode 100644 arch/arm/arm64/include/uk/asm/tls.h create mode 100644 arch/x86/x86_64/include/uk/asm/tls.h create mode 100644 include/uk/arch/tls.h create mode 100644 plat/common/include/tls.h create mode 100644 plat/common/include/x86/tls.h delete mode 100644 plat/linuxu/arm/link.lds create mode 100644 plat/linuxu/arm/link.lds.S rename plat/{common/x86/link64.lds => linuxu/include/tls.h} (77%) delete mode 100644 plat/linuxu/x86/link64.lds create mode 100644 plat/linuxu/x86/link64.lds.S -- 2.21.0 _______________________________________________ Minios-devel mailing list Minios-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/minios-devel

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