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[76.210.143.223]) by smtp.gmail.com with ESMTPSA id u24sm22051028pfm.27.2021.08.24.21.54.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Aug 2021 21:54:35 -0700 (PDT) Date: Tue, 24 Aug 2021 21:54:35 -0700 (PDT) X-Google-Original-Date: Tue, 24 Aug 2021 21:54:31 PDT (-0700) Subject: Re: [PATCH v3] riscv: explicitly use symbol offsets for VDSO In-Reply-To: <20210804173214.1027994-1-abdulras@google.com> CC: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, nathan@kernel.org, ndesaulniers@google.com, morbo@google.com, clang-built-linux@googlegroups.com, abdulras@google.com From: Palmer Dabbelt To: abdulras@google.com Message-ID: Mime-Version: 1.0 (MHng) Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 04 Aug 2021 10:32:14 PDT (-0700), abdulras@google.com wrote: > The current implementation of the `__rt_sigaction` reference computed an > absolute offset relative to the mapped base of the VDSO. While this can > be handled in the medlow model, the medany model cannot handle this as > it is meant to be position independent. The current implementation > relied on the BFD linker relaxing the PC-relative relocation into an > absolute relocation as it was a near-zero address allowing it to be > referenced relative to `zero`. > > We now extract the offsets and create a generated header allowing the > build with LLVM and lld to succeed as we no longer depend on the linker > rewriting address references near zero. This change was largely > modelled after the ARM64 target which does something similar. > > Signed-off-by: Saleem Abdulrasool > --- > arch/riscv/Makefile | 4 ++++ > arch/riscv/include/asm/vdso.h | 14 ++---------- > arch/riscv/kernel/vdso/Makefile | 25 ++++++++++------------ > arch/riscv/kernel/vdso/gen_vdso_offsets.sh | 5 +++++ > arch/riscv/kernel/vdso/so2s.sh | 6 ------ > 5 files changed, 22 insertions(+), 32 deletions(-) > create mode 100755 arch/riscv/kernel/vdso/gen_vdso_offsets.sh > delete mode 100755 arch/riscv/kernel/vdso/so2s.sh > > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile > index bc74afdbf31e..e026b2d0a5a4 100644 > --- a/arch/riscv/Makefile > +++ b/arch/riscv/Makefile > @@ -108,6 +108,10 @@ PHONY += vdso_install > vdso_install: > $(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso $@ > > +prepare: vdso_prepare > +vdso_prepare: prepare0 > + $(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso include/generated/vdso-offsets.h > + > ifneq ($(CONFIG_XIP_KERNEL),y) > ifeq ($(CONFIG_RISCV_M_MODE)$(CONFIG_SOC_CANAAN),yy) > KBUILD_IMAGE := $(boot)/loader.bin > diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h > index 1453a2f563bc..d8d003c2b5a3 100644 > --- a/arch/riscv/include/asm/vdso.h > +++ b/arch/riscv/include/asm/vdso.h > @@ -9,25 +9,15 @@ > #define _ASM_RISCV_VDSO_H > > #include > +#include > > #ifndef CONFIG_GENERIC_TIME_VSYSCALL > struct vdso_data { > }; > #endif > > -/* > - * The VDSO symbols are mapped into Linux so we can just use regular symbol > - * addressing to get their offsets in userspace. The symbols are mapped at an > - * offset of 0, but since the linker must support setting weak undefined > - * symbols to the absolute address 0 it also happens to support other low > - * addresses even when the code model suggests those low addresses would not > - * otherwise be availiable. > - */ > #define VDSO_SYMBOL(base, name) \ > -({ \ > - extern const char __vdso_##name[]; \ > - (void __user *)((unsigned long)(base) + __vdso_##name); \ > -}) > + (void __user *)((unsigned long)(base) + __vdso_##name##_offset) > > asmlinkage long sys_riscv_flush_icache(uintptr_t, uintptr_t, uintptr_t); > > diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile > index 24d936c147cd..f8cb9144a284 100644 > --- a/arch/riscv/kernel/vdso/Makefile > +++ b/arch/riscv/kernel/vdso/Makefile > @@ -23,10 +23,10 @@ ifneq ($(c-gettimeofday-y),) > endif > > # Build rules > -targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.lds vdso-syms.S > +targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.lds > obj-vdso := $(addprefix $(obj)/, $(obj-vdso)) > > -obj-y += vdso.o vdso-syms.o > +obj-y += vdso.o > CPPFLAGS_vdso.lds += -P -C -U$(ARCH) > > # Disable -pg to prevent insert call site > @@ -43,20 +43,22 @@ $(obj)/vdso.o: $(obj)/vdso.so > # link rule for the .so file, .lds has to be first > $(obj)/vdso.so.dbg: $(obj)/vdso.lds $(obj-vdso) FORCE > $(call if_changed,vdsold) > -LDFLAGS_vdso.so.dbg = -shared -s -soname=linux-vdso.so.1 \ > +LDFLAGS_vdso.so.dbg = -shared -S -soname=linux-vdso.so.1 \ > --build-id=sha1 --hash-style=both --eh-frame-hdr > > -# We also create a special relocatable object that should mirror the symbol > -# table and layout of the linked DSO. With ld --just-symbols we can then > -# refer to these symbols in the kernel code rather than hand-coded addresses. > -$(obj)/vdso-syms.S: $(obj)/vdso.so FORCE > - $(call if_changed,so2s) > - > # strip rule for the .so file > $(obj)/%.so: OBJCOPYFLAGS := -S > $(obj)/%.so: $(obj)/%.so.dbg FORCE > $(call if_changed,objcopy) > > +# Generate VDSO offsets using helper script > +gen-vdsosym := $(srctree)/$(src)/gen_vdso_offsets.sh > +quiet_cmd_vdsosym = VDSOSYM $@ > + cmd_vdsosym = $(NM) $< | $(gen-vdsosym) | LC_ALL=C sort > $@ > + > +include/generated/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE > + $(call if_changed,vdsosym) > + > # actual build commands > # The DSO images are built using a special linker script > # Make sure only to export the intended __vdso_xxx symbol offsets. > @@ -65,11 +67,6 @@ quiet_cmd_vdsold = VDSOLD $@ > $(OBJCOPY) $(patsubst %, -G __vdso_%, $(vdso-syms)) $@.tmp $@ && \ > rm $@.tmp > > -# Extracts symbol offsets from the VDSO, converting them into an assembly file > -# that contains the same symbols at the same offsets. > -quiet_cmd_so2s = SO2S $@ > - cmd_so2s = $(NM) -D $< | $(srctree)/$(src)/so2s.sh > $@ > - > # install commands for the unstripped file > quiet_cmd_vdso_install = INSTALL $@ > cmd_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/vdso/$@ > diff --git a/arch/riscv/kernel/vdso/gen_vdso_offsets.sh b/arch/riscv/kernel/vdso/gen_vdso_offsets.sh > new file mode 100755 > index 000000000000..c2e5613f3495 > --- /dev/null > +++ b/arch/riscv/kernel/vdso/gen_vdso_offsets.sh > @@ -0,0 +1,5 @@ > +#!/bin/sh > +# SPDX-License-Identifier: GPL-2.0 > + > +LC_ALL=C > +sed -n -e 's/^[0]\+\(0[0-9a-fA-F]*\) . \(__vdso_[a-zA-Z0-9_]*\)$/\#define \2_offset\t0x\1/p' > diff --git a/arch/riscv/kernel/vdso/so2s.sh b/arch/riscv/kernel/vdso/so2s.sh > deleted file mode 100755 > index e64cb6d9440e..000000000000 > --- a/arch/riscv/kernel/vdso/so2s.sh > +++ /dev/null > @@ -1,6 +0,0 @@ > -#!/bin/sh > -# SPDX-License-Identifier: GPL-2.0+ > -# Copyright 2020 Palmer Dabbelt > - > -sed 's!\([0-9a-f]*\) T \([a-z0-9_]*\)\(@@LINUX_4.15\)*!.global \2\n.set \2,0x\1!' \ > -| grep '^\.' This is on for-next. Thanks!