On Fri, Oct 23, 2020 at 10:03 PM 'Palmer Dabbelt' via Clang Built Linux clang-built-linux@googlegroups.com wrote:
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") Cc: clang-built-linux@googlegroups.com Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt palmerdabbelt@google.com
Any way to improve the error message if/when this fails? https://travis-ci.com/github/ClangBuiltLinux/continuous-integration/jobs/407...
Changes since v2 20201019235630.762886-1-palmerdabbelt@google.com:
- Uses $(srctree)/$(src) to allow for out-of-tree builds.
Changes since v1 20201017002500.503011-1-palmerdabbelt@google.com:
- Uses $(NM) instead of $(CROSS_COMPILE)nm. We use the $(CROSS_COMPILE) form elsewhere in this file, but we'll fix that later.
- Removed the unnecesary .map file creation.
arch/riscv/kernel/vdso/.gitignore | 1 + arch/riscv/kernel/vdso/Makefile | 17 ++++++++--------- arch/riscv/kernel/vdso/so2s.sh | 6 ++++++ 3 files changed, 15 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 11ebee9e4c1d..3a19def868ec 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 478e7338ddc1..a8ecf102e09b 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 $(call if_changed,vdsold) +SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \
-Wl,--build-id -Wl,--hash-style=both# We also create a special relocatable object that should mirror the symbol # table and layout of the linked DSO. With ld --just-symbols we can then # refer to these symbols in the kernel code rather than hand-coded addresses.
-SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \
-Wl,--build-id -Wl,--hash-style=both-$(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 +68,10 @@ quiet_cmd_vdsold = VDSOLD $@ $(patsubst %, -G __vdso_%, $(vdso-syms)) $@.tmp $@ && \ rm $@.tmp
+# Extracts +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 000000000000..3c5b43207658 --- /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 '^.'
2.29.0.rc1.297.gfa9743e501-goog
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