Re: [PATCH V5 16/21] riscv: compat: vdso: Add rv32 VDSO base code implementation

Guo Ren
2022-02-23T09:55:23Z

On Wed, Feb 23, 2022 at 9:42 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Tue, 01 Feb 2022 07:05:40 PST (-0800), guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > There is no vgettimeofday supported in rv32 that makes simple to
> > generate rv32 vdso code which only needs riscv64 compiler. Other
> > architectures need change compiler or -m (machine parameter) to
> > support vdso32 compiling. If rv32 support vgettimeofday (which
> > cause C compile) in future, we would add CROSS_COMPILE to support
> > that makes more requirement on compiler enviornment.
>
> IMO this is the wrong way to go, as there's some subtle differences
> between elf32 and elf64 (the .gnu.hash layout, for example). I'm kind
> of surprised userspace tolerates this sort of thing at all, but given
> how easy it is to target rv32 from all toolchains (we don't need
> libraries here, so just -march should do it) I don't think it's worth
> chasing around the likely long-tail issues that will arise.
I would keep the patch in next version. When "multi-arch toolchain" or
"rv32 HAVE_GENERIC_VDSO" isready in the future, let's switch to the
rv32 compiler.

>
> > linux-rv64/arch/riscv/kernel/compat_vdso/compat_vdso.so.dbg:
> > file format elf64-littleriscv
> >
> > Disassembly of section .text:
> >
> > 0000000000000800 <__vdso_rt_sigreturn>:
> > 800: 08b00893 li a7,139
> > 804: 00000073 ecall
> > 808: 0000 unimp
> > ...
> >
> > 000000000000080c <__vdso_getcpu>:
> > 80c: 0a800893 li a7,168
> > 810: 00000073 ecall
> > 814: 8082 ret
> > ...
> >
> > 0000000000000818 <__vdso_flush_icache>:
> > 818: 10300893 li a7,259
> > 81c: 00000073 ecall
> > 820: 8082 ret
> >
> > linux-rv32/arch/riscv/kernel/vdso/vdso.so.dbg:
> > file format elf32-littleriscv
> >
> > Disassembly of section .text:
> >
> > 00000800 <__vdso_rt_sigreturn>:
> > 800: 08b00893 li a7,139
> > 804: 00000073 ecall
> > 808: 0000 unimp
> > ...
> >
> > 0000080c <__vdso_getcpu>:
> > 80c: 0a800893 li a7,168
> > 810: 00000073 ecall
> > 814: 8082 ret
> > ...
> >
> > 00000818 <__vdso_flush_icache>:
> > 818: 10300893 li a7,259
> > 81c: 00000073 ecall
> > 820: 8082 ret
> >
> > Finally, reuse all *.S from vdso in compat_vdso that makes
> > implementation clear and readable.
> >
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Palmer Dabbelt <palmer@dabbelt.com>
> > ---
> > arch/riscv/Makefile | 5 ++
> > arch/riscv/include/asm/vdso.h | 9 +++
> > arch/riscv/kernel/Makefile | 1 +
> > arch/riscv/kernel/compat_vdso/.gitignore | 2 +
> > arch/riscv/kernel/compat_vdso/Makefile | 68 +++++++++++++++++++
> > arch/riscv/kernel/compat_vdso/compat_vdso.S | 8 +++
> > .../kernel/compat_vdso/compat_vdso.lds.S | 3 +
> > arch/riscv/kernel/compat_vdso/flush_icache.S | 3 +
> > .../compat_vdso/gen_compat_vdso_offsets.sh | 5 ++
> > arch/riscv/kernel/compat_vdso/getcpu.S | 3 +
> > arch/riscv/kernel/compat_vdso/note.S | 3 +
> > arch/riscv/kernel/compat_vdso/rt_sigreturn.S | 3 +
> > arch/riscv/kernel/vdso/vdso.S | 6 +-
> > 13 files changed, 118 insertions(+), 1 deletion(-)
> > create mode 100644 arch/riscv/kernel/compat_vdso/.gitignore
> > create mode 100644 arch/riscv/kernel/compat_vdso/Makefile
> > create mode 100644 arch/riscv/kernel/compat_vdso/compat_vdso.S
> > create mode 100644 arch/riscv/kernel/compat_vdso/compat_vdso.lds.S
> > create mode 100644 arch/riscv/kernel/compat_vdso/flush_icache.S
> > create mode 100755 arch/riscv/kernel/compat_vdso/gen_compat_vdso_offsets.sh
> > create mode 100644 arch/riscv/kernel/compat_vdso/getcpu.S
> > create mode 100644 arch/riscv/kernel/compat_vdso/note.S
> > create mode 100644 arch/riscv/kernel/compat_vdso/rt_sigreturn.S
> >
> > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > index a02e588c4947..f73d50552e09 100644
> > --- a/arch/riscv/Makefile
> > +++ b/arch/riscv/Makefile
> > @@ -106,12 +106,17 @@ libs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
> > PHONY += vdso_install
> > vdso_install:
> > $(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso $@
> > + $(if $(CONFIG_COMPAT),$(Q)$(MAKE) \
> > + $(build)=arch/riscv/kernel/compat_vdso $@)
> >
> > ifeq ($(KBUILD_EXTMOD),)
> > ifeq ($(CONFIG_MMU),y)
> > prepare: vdso_prepare
> > vdso_prepare: prepare0
> > $(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso include/generated/vdso-offsets.h
> > + $(if $(CONFIG_COMPAT),$(Q)$(MAKE) \
> > + $(build)=arch/riscv/kernel/compat_vdso include/generated/compat_vdso-offsets.h)
> > +
> > endif
> > endif
> >
> > diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h
> > index bc6f75f3a199..af981426fe0f 100644
> > --- a/arch/riscv/include/asm/vdso.h
> > +++ b/arch/riscv/include/asm/vdso.h
> > @@ -21,6 +21,15 @@
> >
> > #define VDSO_SYMBOL(base, name) \
> > (void __user *)((unsigned long)(base) + __vdso_##name##_offset)
> > +
> > +#ifdef CONFIG_COMPAT
> > +#include <generated/compat_vdso-offsets.h>
> > +
> > +#define COMPAT_VDSO_SYMBOL(base, name) \
> > + (void __user *)((unsigned long)(base) + compat__vdso_##name##_offset)
> > +
> > +#endif /* CONFIG_COMPAT */
> > +
> > #endif /* !__ASSEMBLY__ */
> >
> > #endif /* CONFIG_MMU */
> > diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> > index 954dc7043ad2..88e79f481c21 100644
> > --- a/arch/riscv/kernel/Makefile
> > +++ b/arch/riscv/kernel/Makefile
> > @@ -67,3 +67,4 @@ obj-$(CONFIG_JUMP_LABEL) += jump_label.o
> >
> > obj-$(CONFIG_EFI) += efi.o
> > obj-$(CONFIG_COMPAT) += compat_syscall_table.o
> > +obj-$(CONFIG_COMPAT) += compat_vdso/
> > diff --git a/arch/riscv/kernel/compat_vdso/.gitignore b/arch/riscv/kernel/compat_vdso/.gitignore
> > new file mode 100644
> > index 000000000000..19d83d846c1e
> > --- /dev/null
> > +++ b/arch/riscv/kernel/compat_vdso/.gitignore
> > @@ -0,0 +1,2 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +compat_vdso.lds
> > diff --git a/arch/riscv/kernel/compat_vdso/Makefile b/arch/riscv/kernel/compat_vdso/Makefile
> > new file mode 100644
> > index 000000000000..7bbbbf94307f
> > --- /dev/null
> > +++ b/arch/riscv/kernel/compat_vdso/Makefile
> > @@ -0,0 +1,68 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +
> > +# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> > +# the inclusion of generic Makefile.
> > +ARCH_REL_TYPE_ABS := R_RISCV_32|R_RISCV_64|R_RISCV_JUMP_SLOT
> > +include $(srctree)/lib/vdso/Makefile
> > +# Symbols present in the compat_vdso
> > +compat_vdso-syms = rt_sigreturn
> > +compat_vdso-syms += getcpu
> > +compat_vdso-syms += flush_icache
> > +
> > +# Files to link into the compat_vdso
> > +obj-compat_vdso = $(patsubst %, %.o, $(compat_vdso-syms)) note.o
> > +
> > +ccflags-y := -fno-stack-protector
> > +
> > +# Build rules
> > +targets := $(obj-compat_vdso) compat_vdso.so compat_vdso.so.dbg compat_vdso.lds
> > +obj-compat_vdso := $(addprefix $(obj)/, $(obj-compat_vdso))
> > +
> > +obj-y += compat_vdso.o
> > +CPPFLAGS_compat_vdso.lds += -P -C -U$(ARCH)
> > +
> > +# Disable profiling and instrumentation for VDSO code
> > +GCOV_PROFILE := n
> > +KCOV_INSTRUMENT := n
> > +KASAN_SANITIZE := n
> > +UBSAN_SANITIZE := n
> > +
> > +# Force dependency
> > +$(obj)/compat_vdso.o: $(obj)/compat_vdso.so
> > +
> > +# link rule for the .so file, .lds has to be first
> > +$(obj)/compat_vdso.so.dbg: $(obj)/compat_vdso.lds $(obj-compat_vdso) FORCE
> > + $(call if_changed,compat_vdsold)
> > +LDFLAGS_compat_vdso.so.dbg = -shared -S -soname=linux-compat_vdso.so.1 \
> > + --build-id=sha1 --hash-style=both --eh-frame-hdr
> > +
> > +# strip rule for the .so file
> > +$(obj)/%.so: OBJCOPYFLAGS := -S
> > +$(obj)/%.so: $(obj)/%.so.dbg FORCE
> > + $(call if_changed,objcopy)
> > +
> > +# Generate VDSO offsets using helper script
> > +gen-compat_vdsosym := $(srctree)/$(src)/gen_compat_vdso_offsets.sh
> > +quiet_cmd_compat_vdsosym = VDSOSYM $@
> > + cmd_compat_vdsosym = $(NM) $< | $(gen-compat_vdsosym) | LC_ALL=C sort > $@
> > +
> > +include/generated/compat_vdso-offsets.h: $(obj)/compat_vdso.so.dbg FORCE
> > + $(call if_changed,compat_vdsosym)
> > +
> > +# actual build commands
> > +# The DSO images are built using a special linker script
> > +# Make sure only to export the intended __compat_vdso_xxx symbol offsets.
> > +quiet_cmd_compat_vdsold = VDSOLD $@
> > + cmd_compat_vdsold = $(LD) $(ld_flags) -T $(filter-out FORCE,$^) -o $@.tmp && \
> > + $(OBJCOPY) $(patsubst %, -G __compat_vdso_%, $(compat_vdso-syms)) $@.tmp $@ && \
> > + rm $@.tmp
> > +
> > +# install commands for the unstripped file
> > +quiet_cmd_compat_vdso_install = INSTALL $@
> > + cmd_compat_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/compat_vdso/$@
> > +
> > +compat_vdso.so: $(obj)/compat_vdso.so.dbg
> > + @mkdir -p $(MODLIB)/compat_vdso
> > + $(call cmd,compat_vdso_install)
> > +
> > +compat_vdso_install: compat_vdso.so
> > diff --git a/arch/riscv/kernel/compat_vdso/compat_vdso.S b/arch/riscv/kernel/compat_vdso/compat_vdso.S
> > new file mode 100644
> > index 000000000000..fea4a8b0c45d
> > --- /dev/null
> > +++ b/arch/riscv/kernel/compat_vdso/compat_vdso.S
> > @@ -0,0 +1,8 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#define vdso_start compat_vdso_start
> > +#define vdso_end compat_vdso_end
> > +
> > +#define __VDSO_PATH "arch/riscv/kernel/compat_vdso/compat_vdso.so"
> > +
> > +#include <../vdso/vdso.S>
> > diff --git a/arch/riscv/kernel/compat_vdso/compat_vdso.lds.S b/arch/riscv/kernel/compat_vdso/compat_vdso.lds.S
> > new file mode 100644
> > index 000000000000..02a9ec5dc7f6
> > --- /dev/null
> > +++ b/arch/riscv/kernel/compat_vdso/compat_vdso.lds.S
> > @@ -0,0 +1,3 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#include <../vdso/vdso.lds.S>
> > diff --git a/arch/riscv/kernel/compat_vdso/flush_icache.S b/arch/riscv/kernel/compat_vdso/flush_icache.S
> > new file mode 100644
> > index 000000000000..88e21a84a974
> > --- /dev/null
> > +++ b/arch/riscv/kernel/compat_vdso/flush_icache.S
> > @@ -0,0 +1,3 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#include <../vdso/flush_icache.S>
> > diff --git a/arch/riscv/kernel/compat_vdso/gen_compat_vdso_offsets.sh b/arch/riscv/kernel/compat_vdso/gen_compat_vdso_offsets.sh
> > new file mode 100755
> > index 000000000000..8ac070c783b3
> > --- /dev/null
> > +++ b/arch/riscv/kernel/compat_vdso/gen_compat_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 compat\2_offset\t0x\1/p'
> > diff --git a/arch/riscv/kernel/compat_vdso/getcpu.S b/arch/riscv/kernel/compat_vdso/getcpu.S
> > new file mode 100644
> > index 000000000000..946449a15a94
> > --- /dev/null
> > +++ b/arch/riscv/kernel/compat_vdso/getcpu.S
> > @@ -0,0 +1,3 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#include <../vdso/getcpu.S>
> > diff --git a/arch/riscv/kernel/compat_vdso/note.S b/arch/riscv/kernel/compat_vdso/note.S
> > new file mode 100644
> > index 000000000000..67c50898b8e5
> > --- /dev/null
> > +++ b/arch/riscv/kernel/compat_vdso/note.S
> > @@ -0,0 +1,3 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#include <../vdso/note.S>
> > diff --git a/arch/riscv/kernel/compat_vdso/rt_sigreturn.S b/arch/riscv/kernel/compat_vdso/rt_sigreturn.S
> > new file mode 100644
> > index 000000000000..f4c98f18c053
> > --- /dev/null
> > +++ b/arch/riscv/kernel/compat_vdso/rt_sigreturn.S
> > @@ -0,0 +1,3 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#include <../vdso/rt_sigreturn.S>
> > diff --git a/arch/riscv/kernel/vdso/vdso.S b/arch/riscv/kernel/vdso/vdso.S
> > index df222245be05..83f1c899e8d8 100644
> > --- a/arch/riscv/kernel/vdso/vdso.S
> > +++ b/arch/riscv/kernel/vdso/vdso.S
> > @@ -7,12 +7,16 @@
> > #include <linux/linkage.h>
> > #include <asm/page.h>
> >
> > +#ifndef __VDSO_PATH
> > +#define __VDSO_PATH "arch/riscv/kernel/vdso/vdso.so"
> > +#endif
> > +
> > __PAGE_ALIGNED_DATA
> >
> > .globl vdso_start, vdso_end
> > .balign PAGE_SIZE
> > vdso_start:
> > - .incbin "arch/riscv/kernel/vdso/vdso.so"
> > + .incbin __VDSO_PATH
> > .balign PAGE_SIZE
> > vdso_end:

--
Best Regards
Guo Ren

ML: https://lore.kernel.org/linux-csky/