vdso: Rename included Makefile

As the Makefile is included into other Makefiles it can not be used to
define objects to be built from the current source directory.
However the generic datastore will

vdso: Rename included Makefile

As the Makefile is included into other Makefiles it can not be used to
define objects to be built from the current source directory.
However the generic datastore will introduce such a local source file.
Rename the included Makefile so it is clear how it is to be used and to
make room for a regular Makefile in lib/vdso/.

Signed-off-by: Thomas Weißschuh <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/all/[email protected]

show more ...

powerpc/Makefile: Allow overriding CPP

Unlike all other arches, powerpc doesn't allow the user to override CPP,
because it sets it unconditionally in the arch Makefile. This can lead
to strange buil

powerpc/Makefile: Allow overriding CPP

Unlike all other arches, powerpc doesn't allow the user to override CPP,
because it sets it unconditionally in the arch Makefile. This can lead
to strange build failures.

Instead add the required flags to KBUILD_CPPFLAGS, which are passed
to CPP, CC and AS invocations by the generic Makefile logic.

Reported-by: Arnd Bergmann <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]
Signed-off-by: Arnd Bergmann <[email protected]>
[mpe: Rebase, write change log, add Arnd's SoB as communicated privately]
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://patch.msgid.link/[email protected]

show more ...

powerpc/vdso: Drop -mstack-protector-guard flags in 32-bit files with clang

Under certain conditions, the 64-bit '-mstack-protector-guard' flags may
end up in the 32-bit vDSO flags, resulting in bui

powerpc/vdso: Drop -mstack-protector-guard flags in 32-bit files with clang

Under certain conditions, the 64-bit '-mstack-protector-guard' flags may
end up in the 32-bit vDSO flags, resulting in build failures due to the
structure of clang's argument parsing of the stack protector options,
which validates the arguments of the stack protector guard flags
unconditionally in the frontend, choking on the 64-bit values when
targeting 32-bit:

clang: error: invalid value 'r13' in 'mstack-protector-guard-reg=', expected one of: r2
clang: error: invalid value 'r13' in 'mstack-protector-guard-reg=', expected one of: r2
make[3]: *** [arch/powerpc/kernel/vdso/Makefile:85: arch/powerpc/kernel/vdso/vgettimeofday-32.o] Error 1
make[3]: *** [arch/powerpc/kernel/vdso/Makefile:87: arch/powerpc/kernel/vdso/vgetrandom-32.o] Error 1

Remove these flags by adding them to the CC32FLAGSREMOVE variable, which
already handles situations similar to this. Additionally, reformat and
align a comment better for the expanding CONFIG_CC_IS_CLANG block.

Cc: [email protected] # v6.1+
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://patch.msgid.link/20241030-powerpc-vdso-drop-stackp-flags-clang-v1-1-d95e7376d29c@kernel.org

show more ...

powerpc/vdso: allow r30 in vDSO code generation of getrandom

For gettimeofday, -ffixed-r30 was passed to work around a bug in Go
code, where the vDSO trampoline forgot to save and restore this regis

powerpc/vdso: allow r30 in vDSO code generation of getrandom

For gettimeofday, -ffixed-r30 was passed to work around a bug in Go
code, where the vDSO trampoline forgot to save and restore this register
across function calls. But Go requires a different trampoline for every
call, and there's no reason that new Go code needs to be broken and add
more bugs. So remove -ffixed-r30 for getrandom.

Fixes: 8072b39c3a75 ("powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO64")
Signed-off-by: Jason A. Donenfeld <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://msgid.link/[email protected]

show more ...

powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO64

Extend getrandom() vDSO implementation to VDSO64.

Tested on QEMU on both ppc64_defconfig and ppc64le_defconfig.

Results from a Power

powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO64

Extend getrandom() vDSO implementation to VDSO64.

Tested on QEMU on both ppc64_defconfig and ppc64le_defconfig.

Results from a Power9 (PowerNV):
~ # ./vdso_test_getrandom bench-single
   vdso: 25000000 times in 0.787943615 seconds
   libc: 25000000 times in 14.101887252 seconds
   syscall: 25000000 times in 14.047475082 seconds

Signed-off-by: Christophe Leroy <[email protected]>
Tested-by: Madhavan Srinivasan <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Signed-off-by: Jason A. Donenfeld <[email protected]>

show more ...

powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO32

To be consistent with other VDSO functions, the function is called
__kernel_getrandom()

__arch_chacha20_blocks_nostack() fonction is

powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO32

To be consistent with other VDSO functions, the function is called
__kernel_getrandom()

__arch_chacha20_blocks_nostack() fonction is implemented basically
with 32 bits operations. It performs 4 QUARTERROUND operations in
parallele. There are enough registers to avoid using the stack:

On input:
r3: output bytes
r4: 32-byte key input
r5: 8-byte counter input/output
r6: number of 64-byte blocks to write to output

During operation:
stack: pointer to counter (r5) and non-volatile registers (r14-131)
r0: counter of blocks (initialised with r6)
r4: Value '4' after key has been read, used for indexing
r5-r12: key
r14-r15: block counter
r16-r31: chacha state

At the end:
r0, r6-r12: Zeroised
r5, r14-r31: Restored

Performance on powerpc 885 (using kernel selftest):
~# ./vdso_test_getrandom bench-single
vdso: 25000000 times in 62.938002291 seconds
libc: 25000000 times in 535.581916866 seconds
syscall: 25000000 times in 531.525042806 seconds

Performance on powerpc 8321 (using kernel selftest):
~# ./vdso_test_getrandom bench-single
vdso: 25000000 times in 16.899318858 seconds
libc: 25000000 times in 131.050596522 seconds
syscall: 25000000 times in 129.794790389 seconds

This first patch adds support for VDSO32. As selftests cannot easily
be generated only for VDSO32, and because the following patch brings
support for VDSO64 anyway, this patch opts out all code in
__arch_chacha20_blocks_nostack() so that vdso_test_chacha will not
fail to compile and will not crash on PPC64/PPC64LE, allthough the
selftest itself will fail.

Signed-off-by: Christophe Leroy <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Signed-off-by: Jason A. Donenfeld <[email protected]>

show more ...

powerpc/vdso: Refactor CFLAGS for CVDSO build

In order to avoid two much duplication when we add new VDSO
functionnalities in C like getrandom, refactor common CFLAGS.

Signed-off-by: Christophe Ler

powerpc/vdso: Refactor CFLAGS for CVDSO build

In order to avoid two much duplication when we add new VDSO
functionnalities in C like getrandom, refactor common CFLAGS.

Signed-off-by: Christophe Leroy <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Signed-off-by: Jason A. Donenfeld <[email protected]>

show more ...

powerpc/vdso32: Add crtsavres

Commit 08c18b63d965 ("powerpc/vdso32: Add missing _restgpr_31_x to fix
build failure") added _restgpr_31_x to the vdso for gettimeofday, but
the work on getrandom shows

powerpc/vdso32: Add crtsavres

Commit 08c18b63d965 ("powerpc/vdso32: Add missing _restgpr_31_x to fix
build failure") added _restgpr_31_x to the vdso for gettimeofday, but
the work on getrandom shows that we will need more of those functions.

Remove _restgpr_31_x and link in crtsavres.o so that we get all
save/restore functions when optimising the kernel for size.

Signed-off-by: Christophe Leroy <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Signed-off-by: Jason A. Donenfeld <[email protected]>

show more ...

Makefile: remove redundant tool coverage variables

Now Kbuild provides reasonable defaults for objtool, sanitizers, and
profilers.

Remove redundant variables.

Note:

This commit changes the covera

Makefile: remove redundant tool coverage variables

Now Kbuild provides reasonable defaults for objtool, sanitizers, and
profilers.

Remove redundant variables.

Note:

This commit changes the coverage for some objects:

- include arch/mips/vdso/vdso-image.o into UBSAN, GCOV, KCOV
- include arch/sparc/vdso/vdso-image-*.o into UBSAN
- include arch/sparc/vdso/vma.o into UBSAN
- include arch/x86/entry/vdso/extable.o into KASAN, KCSAN, UBSAN, GCOV, KCOV
- include arch/x86/entry/vdso/vdso-image-*.o into KASAN, KCSAN, UBSAN, GCOV, KCOV
- include arch/x86/entry/vdso/vdso32-setup.o into KASAN, KCSAN, UBSAN, GCOV, KCOV
- include arch/x86/entry/vdso/vma.o into GCOV, KCOV
- include arch/x86/um/vdso/vma.o into KASAN, GCOV, KCOV

I believe these are positive effects because all of them are kernel
space objects.

Signed-off-by: Masahiro Yamada <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Tested-by: Roberto Sassu <[email protected]>

show more ...

kbuild: use $(src) instead of $(srctree)/$(src) for source directory

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention withou

kbuild: use $(src) instead of $(srctree)/$(src) for source directory

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:

src := $(obj)

When the kernel is built in a separate output directory, $(src) does
not accurately reflect the source directory location. While Kbuild
resolves this discrepancy by specifying VPATH=$(srctree) to search for
source files, it does not cover all cases. For example, when adding a
header search path for local headers, -I$(srctree)/$(src) is typically
passed to the compiler.

This introduces inconsistency between upstream and downstream Makefiles
because $(src) is used instead of $(srctree)/$(src) for the latter.

To address this inconsistency, this commit changes the semantics of
$(src) so that it always points to the directory in the source tree.

Going forward, the variables used in Makefiles will have the following
meanings:

$(obj) - directory in the object tree
$(src) - directory in the source tree (changed by this commit)
$(objtree) - the top of the kernel object tree
$(srctree) - the top of the kernel source tree

Consequently, $(srctree)/$(src) in upstream Makefiles need to be replaced
with $(src).

Signed-off-by: Masahiro Yamada <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>

show more ...

arch: use $(obj)/ instead of $(src)/ for preprocessed linker scripts

These are generated files. Prefix them with $(obj)/ instead of $(src)/.

Signed-off-by: Masahiro Yamada <[email protected]>
Ac

arch: use $(obj)/ instead of $(src)/ for preprocessed linker scripts

These are generated files. Prefix them with $(obj)/ instead of $(src)/.

Signed-off-by: Masahiro Yamada <[email protected]>
Acked-by: Helge Deller <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>

show more ...

powerpc/vdso: No need to undef powerpc for 64-bit build

The vdso Makefile adds -U$(ARCH) to CPPFLAGS for the vdso64.lds linker
script. ARCH is always powerpc, so it becomes -Upowerpc, which means
un

powerpc/vdso: No need to undef powerpc for 64-bit build

The vdso Makefile adds -U$(ARCH) to CPPFLAGS for the vdso64.lds linker
script. ARCH is always powerpc, so it becomes -Upowerpc, which means
undefine the "powerpc" symbol.

But the 64-bit compiler doesn't define powerpc in the first place,
compare:

$ gcc-5.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc -m32 -E -dM - </dev/null | grep -w powerpc
#define powerpc 1
$ gcc-5.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc -m64 -E -dM - </dev/null | grep -w powerpc
$

So there's no need to undefine it for the 64-bit linker script.

Signed-off-by: Michael Ellerman <[email protected]>
Link: https://msgid.link/[email protected]

show more ...

powerpc/build: vdso linker warning for orphan sections

Add --orphan-handlin for vdsos, and adjust vdso linker scripts to deal
with orphan sections.

Signed-off-by: Nicholas Piggin <[email protected]

powerpc/build: vdso linker warning for orphan sections

Add --orphan-handlin for vdsos, and adjust vdso linker scripts to deal
with orphan sections.

Signed-off-by: Nicholas Piggin <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://msgid.link/[email protected]

show more ...

powerpc/vdso: Include CLANG_FLAGS explicitly in ldflags-y

A future change will move CLANG_FLAGS from KBUILD_{A,C}FLAGS to
KBUILD_CPPFLAGS so that '--target' is available while preprocessing.
When th

powerpc/vdso: Include CLANG_FLAGS explicitly in ldflags-y

A future change will move CLANG_FLAGS from KBUILD_{A,C}FLAGS to
KBUILD_CPPFLAGS so that '--target' is available while preprocessing.
When that occurs, the following error appears when building the compat
PowerPC vDSO:

clang: error: unsupported option '-mbig-endian' for target 'x86_64-pc-linux-gnu'
make[3]: *** [.../arch/powerpc/kernel/vdso/Makefile:76: arch/powerpc/kernel/vdso/vdso32.so.dbg] Error 1

Explicitly add CLANG_FLAGS to ldflags-y, so that '--target' will always
be present.

Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

show more ...

vdso: Improve cmd_vdso_check to check all dynamic relocations

The actual intention is that no dynamic relocation exists in the VDSO. For
this the VDSO build validates that the resulting .so file doe

vdso: Improve cmd_vdso_check to check all dynamic relocations

The actual intention is that no dynamic relocation exists in the VDSO. For
this the VDSO build validates that the resulting .so file does not have any
relocations which are specified via $(ARCH_REL_TYPE_ABS) per architecture,
which is fragile as e.g. ARM64 lacks an entry for R_AARCH64_RELATIVE. Aside
of that ARCH_REL_TYPE_ABS is a misnomer as it checks for relative
relocations too.

However, some GNU ld ports produce unneeded R_*_NONE relocation entries. If
a port fails to determine the exact .rel[a].dyn size, the trailing zeros
become R_*_NONE relocations. E.g. ld's powerpc port recently fixed
https://sourceware.org/bugzilla/show_bug.cgi?id=29540). R_*_NONE are
generally a no-op in the dynamic loaders. So just ignore them.

Remove the ARCH_REL_TYPE_ABS defines and just validate that the resulting
.so file does not contain any R_* relocation entries except R_*_NONE.

Signed-off-by: Fangrui Song <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Vincenzo Frascino <[email protected]> # for aarch64
Reviewed-by: Christophe Leroy <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]> # for vDSO, aarch64
Acked-by: Michael Ellerman <[email protected]> (powerpc)
Link: https://lore.kernel.org/r/[email protected]

show more ...

powerpc/kcsan: Add exclusions from instrumentation

Exclude various incompatible compilation units from KCSAN
instrumentation.

Signed-off-by: Rohan McLure <[email protected]>
Signed-off-by: Mich

powerpc/kcsan: Add exclusions from instrumentation

Exclude various incompatible compilation units from KCSAN
instrumentation.

Signed-off-by: Rohan McLure <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

show more ...

powerpc/vdso: Filter clang's auto var init zero enabler when linking

After commit 8d9acfce3332 ("kbuild: Stop using '-Qunused-arguments' with
clang"), the PowerPC vDSO shows the following error with

powerpc/vdso: Filter clang's auto var init zero enabler when linking

After commit 8d9acfce3332 ("kbuild: Stop using '-Qunused-arguments' with
clang"), the PowerPC vDSO shows the following error with clang-13 and
older when CONFIG_INIT_STACK_ALL_ZERO is enabled:

clang: error: argument unused during compilation: '-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang' [-Werror,-Wunused-command-line-argument]

clang-14 added a change to make sure this flag never triggers
-Wunused-command-line-argument, so it is fixed with newer releases. For
older releases that the kernel still supports building with, just filter
out this flag, as has been done for other flags.

Fixes: f0a42fbab447 ("powerpc/vdso: Improve linker flags")
Fixes: 8d9acfce3332 ("kbuild: Stop using '-Qunused-arguments' with clang")
Link: https://github.com/llvm/llvm-project/commit/ca6d5813d17598cd180995fb3bdfca00f364475f
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

show more ...

powerpc/vdso: Remove an unsupported flag from vgettimeofday-32.o with clang

When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it
warns:

clang-16: error: argument unused during comp

powerpc/vdso: Remove an unsupported flag from vgettimeofday-32.o with clang

When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it
warns:

clang-16: error: argument unused during compilation: '-fno-stack-clash-protection' [-Werror,-Wunused-command-line-argument]

This warning happens because vgettimeofday-32.c gets its base CFLAGS
from the main kernel, which may contain flags that are only supported on
a 64-bit target but not a 32-bit one, which is the case here.
-fstack-clash-protection and its negation are only suppported by the
64-bit powerpc target but that flag is included in an invocation for a
32-bit powerpc target, so clang points out that while the flag is one
that it recognizes, it is not actually used by this compiler job.

To eliminate the warning, remove -fno-stack-clash-protection from
vgettimeofday-32.c's CFLAGS when using clang, as has been done for other
flags previously.

Signed-off-by: Nathan Chancellor <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Tested-by: Linux Kernel Functional Testing <[email protected]>
Tested-by: Anders Roxell <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

show more ...

powerpc/vdso: Improve linker flags

When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, there
are several warnings in the PowerPC vDSO:

clang-16: error: -Wl,-soname=linux-vdso32.so.1:

powerpc/vdso: Improve linker flags

When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, there
are several warnings in the PowerPC vDSO:

clang-16: error: -Wl,-soname=linux-vdso32.so.1: 'linker' input unused [-Werror,-Wunused-command-line-argument]
clang-16: error: -Wl,--hash-style=both: 'linker' input unused [-Werror,-Wunused-command-line-argument]
clang-16: error: argument unused during compilation: '-shared' [-Werror,-Wunused-command-line-argument]

clang-16: error: argument unused during compilation: '-nostdinc' [-Werror,-Wunused-command-line-argument]
clang-16: error: argument unused during compilation: '-Wa,-maltivec' [-Werror,-Wunused-command-line-argument]

The first group of warnings point out that linker flags were being added
to all invocations of $(CC), even though they will only be used during
the final vDSO link. Move those flags to ldflags-y.

The second group of warnings are compiler or assembler flags that will
be unused during linking. Filter them out from KBUILD_CFLAGS so that
they are not used during linking.

Additionally, '-z noexecstack' was added directly to the ld_and_check
rule in commit 1d53c0192b15 ("powerpc/vdso: link with -z noexecstack")
but now that there is a common ldflags variable, it can be moved there.

Signed-off-by: Nathan Chancellor <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Tested-by: Linux Kernel Functional Testing <[email protected]>
Tested-by: Anders Roxell <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

show more ...

powerpc/vdso: Remove unused '-s' flag from ASFLAGS

When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it
warns:

clang-16: error: argument unused during compilation: '-s' [-Werror,-W

powerpc/vdso: Remove unused '-s' flag from ASFLAGS

When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it
warns:

clang-16: error: argument unused during compilation: '-s' [-Werror,-Wunused-command-line-argument]

The compiler's '-s' flag is a linking option (it is passed along to the
linker directly), which means it does nothing when the linker is not
invoked by the compiler. The kernel builds all .o files with '-c', which
stops the compilation pipeline before linking, so '-s' can be safely
dropped from ASFLAGS.

Signed-off-by: Nathan Chancellor <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Reviewed-by: Segher Boessenkool <[email protected]>
Tested-by: Linux Kernel Functional Testing <[email protected]>
Tested-by: Anders Roxell <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

show more ...

powerpc/vdso: Skip objtool from running on VDSO files

Do not run objtool on VDSO files, by using OBJECT_FILES_NON_STANDARD.

Suggested-by: Christophe Leroy <[email protected]>
Tested-by: N

powerpc/vdso: Skip objtool from running on VDSO files

Do not run objtool on VDSO files, by using OBJECT_FILES_NON_STANDARD.

Suggested-by: Christophe Leroy <[email protected]>
Tested-by: Naveen N. Rao <[email protected]>
Reviewed-by: Naveen N. Rao <[email protected]>
Reviewed-by: Christophe Leroy <[email protected]>
Acked-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Sathvika Vasireddy <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

show more ...

powerpc/vdso: link with -z noexecstack

With recent binutils, the following warning appears:

VDSO32L arch/powerpc/kernel/vdso/vdso32.so.dbg
/opt/gcc-12.2.0-nolibc/powerpc64-linux/bin/../lib/gcc/po

powerpc/vdso: link with -z noexecstack

With recent binutils, the following warning appears:

VDSO32L arch/powerpc/kernel/vdso/vdso32.so.dbg
/opt/gcc-12.2.0-nolibc/powerpc64-linux/bin/../lib/gcc/powerpc64-linux/12.2.0/../../../../powerpc64-linux/bin/ld: warning: arch/powerpc/kernel/vdso/getcpu-32.o: missing .note.GNU-stack section implies executable stack
/opt/gcc-12.2.0-nolibc/powerpc64-linux/bin/../lib/gcc/powerpc64-linux/12.2.0/../../../../powerpc64-linux/bin/ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker

To avoid that, explicitly tell the linker we don't want executable
stack.

For more explanations, see commit ffcf9c5700e4 ("x86: link vdso
and boot with -z noexecstack --no-warn-rwx-segments")

Signed-off-by: Christophe Leroy <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/b95f2e3216a574837dd61208444e9515c3423da4.1662132312.git.christophe.leroy@csgroup.eu

show more ...

powerpc/vdso: Link with ld.lld when requested

The PowerPC vDSO uses $(CC) to link, which differs from the rest of the
kernel, which uses $(LD) directly. As a result, the default linker of
the compil

powerpc/vdso: Link with ld.lld when requested

The PowerPC vDSO uses $(CC) to link, which differs from the rest of the
kernel, which uses $(LD) directly. As a result, the default linker of
the compiler is used, which may differ from the linker requested by the
builder. For example:

$ make ARCH=powerpc LLVM=1 mrproper defconfig arch/powerpc/kernel/vdso/
...

$ llvm-readelf -p .comment arch/powerpc/kernel/vdso/vdso{32,64}.so.dbg

File: arch/powerpc/kernel/vdso/vdso32.so.dbg
String dump of section '.comment':
[ 0] clang version 14.0.0 (Fedora 14.0.0-1.fc37)

File: arch/powerpc/kernel/vdso/vdso64.so.dbg
String dump of section '.comment':
[ 0] clang version 14.0.0 (Fedora 14.0.0-1.fc37)

LLVM=1 sets LD=ld.lld but ld.lld is not used to link the vDSO; GNU ld is
because "ld" is the default linker for clang on most Linux platforms.

This is a problem for Clang's Link Time Optimization as implemented in
the kernel because use of GNU ld with LTO requires the LLVMgold plugin,
which is not technically supported for ld.bfd per
https://llvm.org/docs/GoldPlugin.html. Furthermore, if LLVMgold.so is
missing from a user's system, the build will fail, even though LTO as it
is implemented in the kernel requires ld.lld to avoid this dependency in
the first place.

Ultimately, the PowerPC vDSO should be converted to compiling and
linking with $(CC) and $(LD) respectively but there were issues last
time this was tried, potentially due to older but supported tool
versions. To avoid regressing GCC + binutils, use the compiler option
'-fuse-ld', which tells the compiler which linker to use when it is
invoked as both the compiler and linker. Use '-fuse-ld=lld' when
LD=ld.lld has been specified (CONFIG_LD_IS_LLD) so that the vDSO is
linked with the same linker as the rest of the kernel.

$ llvm-readelf -p .comment arch/powerpc/kernel/vdso/vdso{32,64}.so.dbg

File: arch/powerpc/kernel/vdso/vdso32.so.dbg
String dump of section '.comment':
[ 0] Linker: LLD 14.0.0
[ 14] clang version 14.0.0 (Fedora 14.0.0-1.fc37)

File: arch/powerpc/kernel/vdso/vdso64.so.dbg
String dump of section '.comment':
[ 0] Linker: LLD 14.0.0
[ 14] clang version 14.0.0 (Fedora 14.0.0-1.fc37)

LD can be a full path to ld.lld, which will not be handled properly by
'-fuse-ld=lld' if the full path to ld.lld is outside of the compiler's
search path. '-fuse-ld' can take a path to the linker but it is
deprecated in clang 12.0.0; '--ld-path' is preferred for this scenario.

Use '--ld-path' if it is supported, as it will handle a full path or
just 'ld.lld' properly. See the LLVM commit below for the full details
of '--ld-path'.

Signed-off-by: Nathan Chancellor <[email protected]>
Tested-by: Alexey Kardashevskiy <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Reviewed-by: Alexey Kardashevskiy <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://github.com/ClangBuiltLinux/linux/issues/774
Link: https://github.com/llvm/llvm-project/commit/1bc5c84710a8c73ef21295e63c19d10a8c71f2f5
Link: https://lore.kernel.org/r/[email protected]

show more ...

powerpc/vdso: Merge vdso64 and vdso32 into a single directory

merge vdso64 into vdso32 and rename it vdso.

Reported-by: kernel test robot <[email protected]>
Signed-off-by: Christophe Leroy <christophe

powerpc/vdso: Merge vdso64 and vdso32 into a single directory

merge vdso64 into vdso32 and rename it vdso.

Reported-by: kernel test robot <[email protected]>
Signed-off-by: Christophe Leroy <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/4dbe05cc130f6a0858d09ac72e436c373cb08b70.1642782130.git.christophe.leroy@csgroup.eu

show more ...