Unverified Commit c2c81bb2 authored by Palmer Dabbelt's avatar Palmer Dabbelt
Browse files

RISC-V: Fix the VDSO symbol generaton for binutils-2.35+ 



We were relying on GNU ld's ability to re-link executable files in order
to extract our VDSO symbols.  This behavior was deemed a bug as of
binutils-2.35 (specifically the binutils-gdb commit a87e1817a4 ("Have
the linker fail if any attempt to link in an executable is made."), but
as that has been backported to at least Debian's binutils-2.34 in may
manifest in other places.

The previous version of this was a bit of a mess: we were linking a
static executable version of the VDSO, containing only a subset of the
input symbols, which we then linked into the kernel.  This worked, but
certainly wasn't a supported path through the toolchain.  Instead this
new version parses the textual output of nm to produce a symbol table.
Both rely on near-zero addresses being linkable, but as we rely on weak
undefined symbols being linkable elsewhere I don't view this as a major
issue.

Fixes: e2c0cdfb ("RISC-V: User-facing API")
Signed-off-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
parent 1074dd44

arch/riscv/kernel/vdso/.gitignore

+1 −0
Original line number Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0-only

vdso.lds

*.tmp

vdso-syms.S

arch/riscv/kernel/vdso/Makefile

+9 −9
Original line number Diff line number Diff line
@@ -43,19 +43,14 @@ $(obj)/vdso.o: $(obj)/vdso.so 
SYSCFLAGS_vdso.so.dbg = $(c_flags)

$(obj)/vdso.so.dbg: $(src)/vdso.lds $(obj-vdso) FORCE

	$(call if_changed,vdsold)

SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \

	-Wl,--build-id -Wl,--hash-style=both



# 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.



SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \

	-Wl,--build-id=sha1 -Wl,--hash-style=both

$(obj)/vdso-dummy.o: $(src)/vdso.lds $(obj)/rt_sigreturn.o FORCE

	$(call if_changed,vdsold)



LDFLAGS_vdso-syms.o := -r --just-symbols

$(obj)/vdso-syms.o: $(obj)/vdso-dummy.o FORCE

	$(call if_changed,ld)

$(obj)/vdso-syms.S: $(obj)/vdso.so FORCE

	$(call if_changed,so2s)



# strip rule for the .so file

$(obj)/%.so: OBJCOPYFLAGS := -S
@@ -73,6 +68,11 @@ quiet_cmd_vdsold = VDSOLD $@ 
                           $(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 $(MODLIB)/vdso/$@

arch/riscv/kernel/vdso/so2s.sh

0 → 100755
+6 −0
Original line number Diff line number Diff line 
#!/bin/sh

# SPDX-License-Identifier: GPL-2.0+

# Copyright 2020 Palmer Dabbelt <palmerdabbelt@google.com>



sed 's!\([0-9a-f]*\) T \([a-z0-9_]*\)\(@@LINUX_4.15\)*!.global \2\n.set \2,0x\1!' \

| grep '^\.'

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