On Thu, Nov 05, 2020 at 08:42:22PM -0800, 'Palmer Dabbelt' via Clang Built Linux wrote:
On Mon, 26 Oct 2020 12:48:08 PDT (-0700), Nick Desaulniers wrote:
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...
Probably, but I can't get that command to actually run this stuff. I tried pulling the commands, but I'm getting some weirdness
$ rm -f arch/riscv/kernel/vdso/vdso-syms.S $ make ARCH=riscv defconfig $ make -j2 AR=llvm-ar 'CC=clang' 'HOSTCC=clang' HOSTLD=ld KCFLAGS=-Wno-implicit-fallthrough LD=riscv64-linux-gnu-ld LLVM_IAS=1 NM=llvm-nm OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-size READELF=llvm-readelf STRIP=llvm-strip ARCH=riscv Image
This command is simpler and reproduces it for me locally on next-20201105.
$ make -skj"$(nproc)" ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- LD=riscv64-linux-gnu-ld LLVM=1 distclean defconfig Image clang-12: warning: argument unused during compilation: '-no-pie' [-Wunused-command-line-argument] make[4]: *** [arch/riscv/kernel/vdso/Makefile:53: arch/riscv/kernel/vdso/vdso-syms.S] Error 1 make[4]: *** Deleting file 'arch/riscv/kernel/vdso/vdso-syms.S' make[4]: Target '__build' not remade because of errors. make[3]: *** [scripts/Makefile.build:500: arch/riscv/kernel/vdso] Error 2 make[3]: Target '__build' not remade because of errors. make[2]: *** [scripts/Makefile.build:500: arch/riscv/kernel] Error 2 make[2]: Target '__build' not remade because of errors. make[1]: *** [Makefile:1797: arch/riscv] Error 2 make[1]: Target 'Image' not remade because of errors. make: *** [Makefile:335: __build_one_by_one] Error 2 make: Target 'distclean' not remade because of errors. make: Target 'defconfig' not remade because of errors. make: Target 'Image' not remade because of errors.
<snip>
diff --git a/arch/riscv/kernel/vdso/.gitignore b/arch/riscv/kernel/vdso/.gitignore index 3a19def868ec..88206dd8b472 100644 --- a/arch/riscv/kernel/vdso/.gitignore +++ b/arch/riscv/kernel/vdso/.gitignore @@ -2,3 +2,4 @@ vdso.lds *.tmp vdso-syms.S +vdso-syms.nm diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile index a8ecf102e09b..fe5c969a6bf4 100644 --- a/arch/riscv/kernel/vdso/Makefile +++ b/arch/riscv/kernel/vdso/Makefile @@ -49,8 +49,11 @@ SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \ # We also create a special relocatable object that should mirror the symbol # table and layout of the linked DSO. With ld --just-symbols we can then # refer to these symbols in the kernel code rather than hand-coded addresses. -$(obj)/vdso-syms.S: $(obj)/vdso.so FORCE
- $(call if_changed,so2s)
+$(obj)/vdso-syms.nm: $(obj)/vdso.so
- $(call if_changed,nm_d)
+$(obj)/vdso-syms.S: $(obj)/vdso-syms.nm
- $(call if_changed,nm2s)
# strip rule for the .so file $(obj)/%.so: OBJCOPYFLAGS := -S @@ -68,9 +71,13 @@ 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 > $@+# Extracts symbol offsets from the VDSO, converting them into an assembly file +# that contains the same symbols at the same offsets. +quiet_cmd_nm_d = NM -D $@
cmd_nm_d = $(NM) -D $< > $@+quiet_cmd_nm2s = SYMS2S $@
cmd_nm2s = cat $< | $(srctree)/$(src)/so2s.sh > $@# install commands for the unstripped file quiet_cmd_vdso_install = INSTALL $@
For reference, here's the output of nmo for me:
$ cat arch/riscv/kernel/vdso/vdso-syms.nm 0000000000000000 A LINUX_4.15 00000000000009e0 T __vdso_clock_getres@@LINUX_4.15 000000000000080a T __vdso_clock_gettime@@LINUX_4.15 0000000000000a48 T __vdso_flush_icache@@LINUX_4.15 0000000000000a3c T __vdso_getcpu@@LINUX_4.15 0000000000000916 T __vdso_gettimeofday@@LINUX_4.15 0000000000000800 T __vdso_rt_sigreturn@@LINUX_4.15
This diff does not solve the issue for me with the above command.
Cheers, Nathan