[PATCH 5.9 070/255] RISC-V: Fix the VDSO symbol generaton for binutils-2.35+

Greg Kroah-Hartman
2020-11-17T13:33:48Z

From: Palmer Dabbelt <palmerdabbelt@google.com>

[ Upstream commit c2c81bb2f69138f902e1a58d3bef6ad97fb8a92c ]

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: e2c0cdfba7f6 ("RISC-V: User-facing API")
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/riscv/kernel/vdso/.gitignore | 1 +
arch/riscv/kernel/vdso/Makefile | 18 +++++++++---------
arch/riscv/kernel/vdso/so2s.sh | 6 ++++++
3 files changed, 16 insertions(+), 9 deletions(-)
create mode 100755 arch/riscv/kernel/vdso/so2s.sh

diff --git a/arch/riscv/kernel/vdso/.gitignore b/arch/riscv/kernel/vdso/.gitignore
index 11ebee9e4c1d6..3a19def868ecc 100644
--- a/arch/riscv/kernel/vdso/.gitignore
+++ b/arch/riscv/kernel/vdso/.gitignore
@@ -1,3 +1,4 @@
# SPDX-License-Identifier: GPL-2.0-only
vdso.lds
*.tmp
+vdso-syms.S
diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
index 7d6a94d45ec94..cb8f9e4cfcbf8 100644
--- a/arch/riscv/kernel/vdso/Makefile
+++ b/arch/riscv/kernel/vdso/Makefile
@@ -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 $(MODLIB)/vdso/$@
diff --git a/arch/riscv/kernel/vdso/so2s.sh b/arch/riscv/kernel/vdso/so2s.sh
new file mode 100755
index 0000000000000..e64cb6d9440e7
--- /dev/null
+++ b/arch/riscv/kernel/vdso/so2s.sh
@@ -0,0 +1,6 @@
+#!/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 '^\.'
--
2.27.0