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Thu, 10 Sep 2020 02:54:58 -0700 (PDT) Date: Thu, 10 Sep 2020 10:54:54 +0100 From: Andrew Scull To: David Brazdil Subject: Re: [PATCH v2 02/10] kvm: arm64: Partially link nVHE hyp code, simplify HYPCOPY Message-ID: <20200910095454.GB93664@google.com> References: <20200903091712.46456-1-dbrazdil@google.com> <20200903091712.46456-3-dbrazdil@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200903091712.46456-3-dbrazdil@google.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200910_055502_660993_777F00C3 X-CRM114-Status: GOOD ( 33.13 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, kernel-team@android.com, Arnd Bergmann , Suzuki K Poulose , Marc Zyngier , linux-kernel@vger.kernel.org, James Morse , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Tejun Heo , Dennis Zhou , Christoph Lameter , Will Deacon , kvmarm@lists.cs.columbia.edu, Julien Thierry Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Sep 03, 2020 at 11:17:04AM +0200, 'David Brazdil' via kernel-team wrote: > Previous series introduced custom build rules for nVHE hyp code, using > objcopy to prefix ELF section and symbol names to separate nVHE code > into its own "namespace". This approach was limited by the expressiveness > of objcopy's command line interface, eg. missing support for wildcards. > > Improve the build rules by partially linking all '.hyp.o' files and > prefixing their ELF section names using a linker script. Continue using > objcopy for prefixing ELF symbol names. > > One immediate advantage of this approach is that all subsections > matching a pattern can be merged into a single prefixed section, eg. > .text and .text.* can be linked into a single '.hyp.text'. This removes > the need for -fno-reorder-functions on GCC and will be useful in the > future too: LTO builds use .text subsections, compilers routinely > generate .rodata subsections, etc. This certaintly feels like a more robust and controlled approach to the sections now that we have an explicit list of those that are allowed. > Partially linking all hyp code into a single object file also makes it > easier to analyze. > > Signed-off-by: David Brazdil > --- > arch/arm64/kvm/hyp/nvhe/Makefile | 56 ++++++++++++++++--------------- > arch/arm64/kvm/hyp/nvhe/hyp.lds.S | 14 ++++++++ > 2 files changed, 43 insertions(+), 27 deletions(-) > create mode 100644 arch/arm64/kvm/hyp/nvhe/hyp.lds.S > > diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile > index aef76487edc2..1b2fbb19f3e8 100644 > --- a/arch/arm64/kvm/hyp/nvhe/Makefile > +++ b/arch/arm64/kvm/hyp/nvhe/Makefile > @@ -10,40 +10,42 @@ obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o > obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \ > ../fpsimd.o ../hyp-entry.o > > -obj-y := $(patsubst %.o,%.hyp.o,$(obj-y)) > -extra-y := $(patsubst %.hyp.o,%.hyp.tmp.o,$(obj-y)) > +## > +## Build rules for compiling nVHE hyp code > +## Output of this folder is `hyp.o`, a partially linked object file containing > +## all nVHE hyp code and data. > +## > > -$(obj)/%.hyp.tmp.o: $(src)/%.c FORCE > +hyp-obj := $(patsubst %.o,%.hyp.o,$(obj-y)) > +obj-y := hyp.o > +extra-y := $(hyp-obj) hyp.tmp.o hyp.lds > + > +# 1) Compile all source files to `.hyp.o` object files. The file extension > +# avoids file name clashes for files shared with VHE. Very much a nit, but possibly .nvhe.o or .kvm_nvhe.o would make the intended distinction more obvious and line up with the prefix being applied to the symbols. > +$(obj)/%.hyp.o: $(src)/%.c FORCE > $(call if_changed_rule,cc_o_c) > -$(obj)/%.hyp.tmp.o: $(src)/%.S FORCE > +$(obj)/%.hyp.o: $(src)/%.S FORCE > $(call if_changed_rule,as_o_S) > -$(obj)/%.hyp.o: $(obj)/%.hyp.tmp.o FORCE > - $(call if_changed,hypcopy) > > -# Disable reordering functions by GCC (enabled at -O2). > -# This pass puts functions into '.text.*' sections to aid the linker > -# in optimizing ELF layout. See HYPCOPY comment below for more info. > -ccflags-y += $(call cc-option,-fno-reorder-functions) > +# 2) Compile linker script. > +$(obj)/hyp.lds: $(src)/hyp.lds.S FORCE > + $(call if_changed_dep,cpp_lds_S) > + > +# 3) Partially link all '.hyp.o' files and apply the linker script. > +# Prefixes names of ELF sections with '.hyp', eg. '.hyp.text'. > +LDFLAGS_hyp.tmp.o := -r -T $(obj)/hyp.lds > +$(obj)/hyp.tmp.o: $(addprefix $(obj)/,$(hyp-obj)) $(obj)/hyp.lds FORCE > + $(call if_changed,ld) > + > +# 4) Produce the final 'hyp.o', ready to be linked into 'vmlinux'. > +# Prefixes names of ELF symbols with '__kvm_nvhe_'. > +$(obj)/hyp.o: $(obj)/hyp.tmp.o FORCE > + $(call if_changed,hypcopy) > > # The HYPCOPY command uses `objcopy` to prefix all ELF symbol names > -# and relevant ELF section names to avoid clashes with VHE code/data. > -# > -# Hyp code is assumed to be in the '.text' section of the input object > -# files (with the exception of specialized sections such as > -# '.hyp.idmap.text'). This assumption may be broken by a compiler that > -# divides code into sections like '.text.unlikely' so as to optimize > -# ELF layout. HYPCOPY checks that no such sections exist in the input > -# using `objdump`, otherwise they would be linked together with other > -# kernel code and not memory-mapped correctly at runtime. > +# to avoid clashes with VHE code/data. > quiet_cmd_hypcopy = HYPCOPY $@ > - cmd_hypcopy = \ > - if $(OBJDUMP) -h $< | grep -F '.text.'; then \ > - echo "$@: function reordering not supported in nVHE hyp code" >&2; \ > - /bin/false; \ > - fi; \ > - $(OBJCOPY) --prefix-symbols=__kvm_nvhe_ \ > - --rename-section=.text=.hyp.text \ > - $< $@ > + cmd_hypcopy = $(OBJCOPY) --prefix-symbols=__kvm_nvhe_ $< $@ > > # Remove ftrace and Shadow Call Stack CFLAGS. > # This is equivalent to the 'notrace' and '__noscs' annotations. > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S > new file mode 100644 > index 000000000000..aaa0ce133a32 > --- /dev/null > +++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S > @@ -0,0 +1,14 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Linker script used during partial linking of nVHE EL2 object files. > + * Written by David Brazdil > + */ Should this file have the standard copyright line? > + > +/* > + * Defines an ELF hyp section from input section @NAME and its subsections. > + */ > +#define HYP_SECTION(NAME) .hyp##NAME : { *(NAME NAME##.[0-9a-zA-Z_]*) } > + > +SECTIONS { > + HYP_SECTION(.text) > +} > -- > 2.28.0.402.g5ffc5be6b7-goog > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel