linux.git/arch/riscv/kernel/vdso, branch v5.14

riscv: vdso: fix and clean-up Makefile

2021-04-26T15:25:19+00:00

Running "make" on an already compiled kernel tree will rebuild the
kernel even without any modifications:

  CALL    linux/scripts/checksyscalls.sh
  CALL    linux/scripts/atomic/check-atomics.sh
  CHK     include/generated/compile.h
  SO2S    arch/riscv/kernel/vdso/vdso-syms.S
  AS      arch/riscv/kernel/vdso/vdso-syms.o
  AR      arch/riscv/kernel/vdso/built-in.a
  AR      arch/riscv/kernel/built-in.a
  AR      arch/riscv/built-in.a
  GEN     .version
  CHK     include/generated/compile.h
  UPD     include/generated/compile.h
  CC      init/version.o
  AR      init/built-in.a
  LD      vmlinux.o

The reason is "Any target that utilizes if_changed must be listed in
$(targets), otherwise the command line check will fail, and the target
will always be built" as explained by Documentation/kbuild/makefiles.rst

Fix this build bug by adding vdso-syms.S to $(targets)

At the same time, there are two trivial clean up modifications:

- the vdso-dummy.o is not needed any more after so remove it.

- vdso.lds is a generated file, so it should be prefixed with
  $(obj)/ instead of $(src)/

Fixes: c2c81bb2f691 ("RISC-V: Fix the VDSO symbol generaton for binutils-2.35+")
Cc: stable@vger.kernel.org
Signed-off-by: Jisheng Zhang 
Signed-off-by: Palmer Dabbelt

riscv: Use $(LD) instead of $(CC) to link vDSO

2021-04-26T15:24:59+00:00

Currently, the VDSO is being linked through $(CC). This does not match
how the rest of the kernel links objects, which is through the $(LD)
variable.

When linking with clang, there are a couple of warnings about flags that
will not be used during the link:

clang-12: warning: argument unused during compilation: '-no-pie' [-Wunused-command-line-argument]
clang-12: warning: argument unused during compilation: '-pg' [-Wunused-command-line-argument]

'-no-pie' was added in commit 85602bea297f ("RISC-V: build vdso-dummy.o
with -no-pie") to override '-pie' getting added to the ld command from
distribution versions of GCC that enable PIE by default. It is
technically no longer needed after commit c2c81bb2f691 ("RISC-V: Fix the
VDSO symbol generaton for binutils-2.35+"), which removed vdso-dummy.o
in favor of generating vdso-syms.S from vdso.so with $(NM) but this also
resolves the issue in case it ever comes back due to having full control
over the $(LD) command. '-pg' is for function tracing, it is not used
during linking as clang states.

These flags could be removed/filtered to fix the warnings but it is
easier to just match the rest of the kernel and use $(LD) directly for
linking. See commits

  fe00e50b2db8 ("ARM: 8858/1: vdso: use $(LD) instead of $(CC) to link VDSO")
  691efbedc60d ("arm64: vdso: use $(LD) instead of $(CC) to link VDSO")
  2ff906994b6c ("MIPS: VDSO: Use $(LD) instead of $(CC) to link VDSO")
  2b2a25845d53 ("s390/vdso: Use $(LD) instead of $(CC) to link vDSO")

for more information.

The flags are converted to linker flags and '--eh-frame-hdr' is added to
match what is added by GCC implicitly, which can be seen by adding '-v'
to GCC's invocation.

Additionally, since this area is being modified, use the $(OBJCOPY)
variable instead of an open coded $(CROSS_COMPILE)objcopy so that the
user's choice of objcopy binary is respected.

Link: https://github.com/ClangBuiltLinux/linux/issues/803
Link: https://github.com/ClangBuiltLinux/linux/issues/970
Signed-off-by: Nathan Chancellor 
Reviewed-by: Fangrui Song 
Signed-off-by: Palmer Dabbelt

riscv: Disable KSAN_SANITIZE for vDSO

2021-02-23T01:51:23+00:00

We use the generic C VDSO implementations of a handful of clock-related
functions.  When kasan is enabled this results in asan stub calls that
are unlikely to be resolved by userspace, this just disables KASAN
when building the VDSO.

Verified the fix on a kernel with KASAN enabled using vDSO selftests.

Link: https://lore.kernel.org/lkml/CACT4Y+ZNJBnkKHXUf=tm_yuowvZvHwN=0rmJ=7J+xFd+9r_6pQ@mail.gmail.com/
Tested-by: Tobias Klauser 
Signed-off-by: Tobias Klauser 
Tested-by: Dmitry Vyukov 
[Palmer: commit text]
Fixes: ad5d1122b82f ("riscv: use vDSO common flow to reduce the latency of the time-related functions")
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt

riscv: Explicitly specify the build id style in vDSO Makefile again

2020-11-25T17:44:14+00:00

Commit a96843372331 ("kbuild: explicitly specify the build id style")
explicitly set the build ID style to SHA1. Commit c2c81bb2f691 ("RISC-V:
Fix the VDSO symbol generaton for binutils-2.35+") undid this change,
likely unintentionally.

Restore it so that the build ID style stays consistent across the tree
regardless of linker.

Fixes: c2c81bb2f691 ("RISC-V: Fix the VDSO symbol generaton for binutils-2.35+")
Signed-off-by: Nathan Chancellor 
Reviewed-by: Nick Desaulniers 
Reviewed-by: Bill Wendling 
Signed-off-by: Palmer Dabbelt

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

2020-11-06T08:03:48+00:00

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

kbuild: explicitly specify the build id style

2020-10-09T14:57:30+00:00

ld's --build-id defaults to "sha1" style, while lld defaults to "fast".
The build IDs are very different between the two, which may confuse
programs that reference them.

Signed-off-by: Bill Wendling 
Acked-by: David S. Miller 
Signed-off-by: Masahiro Yamada

riscv: disable stack-protector for vDSO

2020-08-04T22:02:49+00:00

Currently, building the vDSO with clang leads assembler errors like the
following:

  /tmp/vgettimeofday-1ae0d2.s: Assembler messages:
  /tmp/vgettimeofday-1ae0d2.s:28: Error: bad expression
  /tmp/vgettimeofday-1ae0d2.s:28: Error: illegal operands `auipc a2,%got_pcrel_hi(__stack_chk_guard)'

Disable the stack-protector for vDSO to fix these.

Link: https://github.com/ClangBuiltLinux/linux/issues/1112
Signed-off-by: Tobias Klauser 
Signed-off-by: Palmer Dabbelt

riscv: Allow building with kcov coverage

2020-07-30T18:37:35+00:00

Add ARCH_HAS_KCOV and HAVE_GCC_PLUGINS to the riscv Kconfig.
Also disable instrumentation of some early boot code and vdso.

Boot-tested on QEMU's riscv64 virt machine.

Signed-off-by: Tobias Klauser 
Acked-by: Dmitry Vyukov 
Signed-off-by: Palmer Dabbelt

riscv: Fixup __vdso_gettimeofday broke dynamic ftrace

2020-06-25T22:38:39+00:00

For linux-5.8-rc1, enable ftrace of riscv will cause boot panic:

[    2.388980] Run /sbin/init as init process
[    2.529938] init[39]: unhandled signal 4 code 0x1 at 0x0000003ff449e000
[    2.531078] CPU: 0 PID: 39 Comm: init Not tainted 5.8.0-rc1-dirty #13
[    2.532719] epc: 0000003ff449e000 ra : 0000003ff449e954 sp : 0000003fffedb900
[    2.534005]  gp : 00000000000e8528 tp : 0000003ff449d800 t0 : 000000000000001e
[    2.534965]  t1 : 000000000000000a t2 : 0000003fffedb89e s0 : 0000003fffedb920
[    2.536279]  s1 : 0000003fffedb940 a0 : 0000003ff43d4b2c a1 : 0000000000000000
[    2.537334]  a2 : 0000000000000001 a3 : 0000000000000000 a4 : fffffffffbad8000
[    2.538466]  a5 : 0000003ff449e93a a6 : 0000000000000000 a7 : 0000000000000000
[    2.539511]  s2 : 0000000000000000 s3 : 0000003ff448412c s4 : 0000000000000010
[    2.541260]  s5 : 0000000000000016 s6 : 00000000000d0a30 s7 : 0000003fffedba70
[    2.542152]  s8 : 0000000000000000 s9 : 0000000000000000 s10: 0000003fffedb960
[    2.543335]  s11: 0000000000000000 t3 : 0000000000000000 t4 : 0000003fffedb8a0
[    2.544471]  t5 : 0000000000000000 t6 : 0000000000000000
[    2.545730] status: 0000000000004020 badaddr: 00000000464c457f cause: 0000000000000002
[    2.549867] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
[    2.551267] CPU: 0 PID: 1 Comm: init Not tainted 5.8.0-rc1-dirty #13
[    2.552061] Call Trace:
[    2.552626] [] walk_stackframe+0x0/0xc4
[    2.553486] [] show_stack+0x40/0x4c
[    2.553995] [] dump_stack+0x7a/0x98
[    2.554615] [] panic+0x114/0x2f4
[    2.555395] [] do_exit+0x89c/0x8c2
[    2.555949] [] do_group_exit+0x3a/0x90
[    2.556715] [] get_signal+0xe2/0x6e6
[    2.557388] [] do_notify_resume+0x6a/0x37a
[    2.558089] [] ret_from_exception+0x0/0xc

"ra:0x3ff449e954" is the return address of "call _mcount" in the
prologue of __vdso_gettimeofday(). Without proper relocate, pc jmp
to 0x0000003ff449e000 (vdso map base) with a illegal instruction
trap.

The solution comes from arch/arm64/kernel/vdso/Makefile:

CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS)

 - CC_FLAGS_SCS is ShadowCallStack feature in Clang and only
   implemented for arm64, no use for riscv.

Fixes: ad5d1122b82f ("riscv: use vDSO common flow to reduce the latency of the time-related functions")
Cc: stable@vger.kernel.org
Signed-off-by: Guo Ren 
Reviewed-by: Vincent Chen 
Signed-off-by: Palmer Dabbelt

riscv: Add extern declarations for vDSO time-related functions

2020-06-25T22:15:51+00:00

Add extern declarations for vDSO time-related functions to notify the
compiler these functions will be used in somewhere to avoid
"no previous prototype" compile warning.

Reported-by: kernel test robot 
Signed-off-by: Vincent Chen 
Signed-off-by: Palmer Dabbelt