This patch replaces the "open-coded" -pg compile flag with a CC_FLAGS_FTRACE
makefile variable which architectures can override if a different option
should be used for code generation.

Signed-off-by: zhaoxiao <zhaoxiao@uniontech.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Commit ee67855ecd9d ("MIPS: vdso: Allow clang's --target flag in VDSO
cflags") allowed the '--target=' flag from the main Makefile to filter
through to the vDSO. However, it did not bring any of the other clang
specific flags for controlling the integrated assembler and the GNU
tools locations (--prefix=, --gcc-toolchain=, and -no-integrated-as).
Without these, we will get a warning (visible with tinyconfig):

arch/mips/vdso/elf.S:14:1: warning: DWARF2 only supports one section per
compilation unit
.pushsection .note.Linux, "a",@note ; .balign 4 ; .long 2f - 1f ; .long
4484f - 3f ; .long 0 ; 1:.asciz "Linux" ; 2:.balign 4 ; 3:
^
arch/mips/vdso/elf.S:34:2: warning: DWARF2 only supports one section per
compilation unit
 .section .mips_abiflags, "a"
 ^

All of these flags are bundled up under CLANG_FLAGS in the main Makefile
and exported so that they can be added to Makefiles that set their own
CFLAGS. Use this value instead of filtering out '--target=' so there is
no warning and all of the tools are properly used.

Cc: stable@vger.kernel.org
Fixes: ee67855ecd9d ("MIPS: vdso: Allow clang's --target flag in VDSO cflags")
Link: https://github.com/ClangBuiltLinux/linux/issues/1256
Reported-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

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 <morbo@google.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Some Makefiles already pass -fno-stack-protector unconditionally.
For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.

No problem report so far about hard-coding this option. So, we can
assume all supported compilers know -fno-stack-protector.

GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)

Get rid of cc-option from -fno-stack-protector.

Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which is always 'y'.

Note:
arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
unconditionally, and second conditionally. I removed the second one.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

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 clang is built in a default configuration, it first attempts to use
the target triple's default linker then the system's default linker,
unless told otherwise through -fuse-ld=... We do not use -fuse-ld=
because it can be brittle and we have support for invoking $(LD)
directly. See commit fe00e50b2db8c ("ARM: 8858/1: vdso: use $(LD)
instead of $(CC) to link VDSO") and commit 691efbedc60d2 ("arm64: vdso:
use $(LD) instead of $(CC) to link VDSO") for examples of doing this in
the VDSO.

Do the same thing here. Replace the custom linking logic with $(cmd_ld)
and ldflags-y so that $(LD) is respected. We need to explicitly add two
flags to the linker that were implicitly passed by the compiler:
-G 0 (which comes from ccflags-vdso) and --eh-frame-hdr.

Before this patch (generated by adding '-v' to VDSO_LDFLAGS):

<gcc_prefix>/libexec/gcc/mips64-linux/9.3.0/collect2 \
-plugin <gcc_prefix>/libexec/gcc/mips64-linux/9.3.0/liblto_plugin.so \
-plugin-opt=<gcc_prefix>/libexec/gcc/mips64-linux/9.3.0/lto-wrapper \
-plugin-opt=-fresolution=/tmp/ccGEi5Ka.res \
--eh-frame-hdr \
-G 0 \
-EB \
-mips64r2 \
-shared \
-melf64btsmip \
-o arch/mips/vdso/vdso.so.dbg.raw \
-L<gcc_prefix>/lib/gcc/mips64-linux/9.3.0/64 \
-L<gcc_prefix>/lib/gcc/mips64-linux/9.3.0 \
-L<gcc_prefix>/lib/gcc/mips64-linux/9.3.0/../../../../mips64-linux/lib \
-Bsymbolic \
--no-undefined \
-soname=linux-vdso.so.1 \
-EB \
--hash-style=sysv \
--build-id \
-T arch/mips/vdso/vdso.lds \
arch/mips/vdso/elf.o \
arch/mips/vdso/vgettimeofday.o \
arch/mips/vdso/sigreturn.o

After this patch:

<gcc_prefix>/bin/mips64-linux-ld \
-m elf64btsmip \
-Bsymbolic \
--no-undefined \
-soname=linux-vdso.so.1 \
-EB \
-nostdlib \
-shared \
-G 0 \
--eh-frame-hdr \
--hash-style=sysv \
--build-id \
-T  arch/mips/vdso/vdso.lds \
arch/mips/vdso/elf.o \
arch/mips/vdso/vgettimeofday.o
arch/mips/vdso/sigreturn.o \
-o arch/mips/vdso/vdso.so.dbg.raw

Note that we leave behind -mips64r2. Turns out that ld ignores it (see
get_emulation in ld/ldmain.c). This is true of current trunk and 2.23,
which is the minimum supported version for the kernel:

https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/ldmain.c;hb=aa4209e7b679afd74a3860ce25659e71cc4847d5#l593
https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/ldmain.c;hb=a55e30b51bc6227d8d41f707654d0a5620978dcf#l641

Before this patch, LD=ld.lld did nothing:

$ llvm-readelf -p.comment arch/mips/vdso/vdso.so.dbg | sed 's/(.*//'
String dump of section '.comment':
[     0] ClangBuiltLinux clang version 11.0.0

After this patch, it does:

$ llvm-readelf -p.comment arch/mips/vdso/vdso.so.dbg | sed 's/(.*//'
String dump of section '.comment':
[     0] Linker: LLD 11.0.0
[    62] ClangBuiltLinux clang version 11.0.0

Link: https://github.com/ClangBuiltLinux/linux/issues/785
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

After commit 9553d16fa671 ("init/kconfig: Add LD_VERSION Kconfig"), we
have access to GNU ld's version at configuration time. As a result, we
can make it clearer under what configuration circumstances the MIPS VDSO
needs to be disabled.

This is a prerequisite for getting rid of the MIPS VDSO binutils
warning and linking the VDSO when LD is ld.lld. Wrapping the call to
ld-ifversion with CONFIG_LD_IS_LLD does not work because the config
values are wiped away during 'make clean'.

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Clang does not support this option and errors out:

clang-11: error: unknown argument: '-mexplicit-relocs'

Clang does not appear to need this flag like GCC does because the jalr
check that was added in commit 976c23af3ee5 ("mips: vdso: add build
time check that no 'jalr t9' calls left") passes just fine with

$ make ARCH=mips CC=clang CROSS_COMPILE=mipsel-linux-gnu- malta_defconfig arch/mips/vdso/

even before commit d3f703c4359f ("mips: vdso: fix 'jalr t9' crash in
vdso code").

-mrelax-pic-calls has been supported since clang 9, which is the
earliest version that could build a working MIPS kernel, and it is the
default for clang so just leave it be.

Fixes: d3f703c4359f ("mips: vdso: fix 'jalr t9' crash in vdso code")
Link: https://github.com/ClangBuiltLinux/linux/issues/890
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: clang-built-linux@googlegroups.com

vdso shared object cannot have GOT based PIC 'jalr t9' calls
because nobody set GOT table in vdso. Contributing into vdso
.o files are compiled in PIC mode and as result for internal
static functions calls compiler will generate 'jalr t9'
instructions. Those are supposed to be converted into PC
relative 'bal' calls by linker when relocation are processed.

Mips global GOT entries do have dynamic relocations and they
will be caught by cmd_vdso_check Makefile rule. Static PIC
calls go through mips local GOT entries that do not have
dynamic relocations. For those 'jalr t9' calls could be present
but without dynamic relocations and they need to be converted
to 'bal' calls by linker.

Add additional build time check to make sure that no 'jalr t9'
slip through because of some toolchain misconfiguration that
prevents 'jalr t9' to 'bal' conversion.

Signed-off-by: Victor Kamensky <kamensky@cisco.com>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: bruce.ashfield@gmail.com
Cc: richard.purdie@linuxfoundation.org

A check we're about to add to pick up on function calls that depend on
bogus use of the GOT in the VDSO picked up on instances of such function
calls in microMIPS builds. Since the code appears genuinely problematic,
and given the relatively small amount of use & testing that microMIPS
sees, go ahead & disable the VDSO for microMIPS builds.

Signed-off-by: Paul Burton <paulburton@kernel.org>

Observed that when kernel is built with Yocto mips64-poky-linux-gcc,
and mips64-poky-linux-gnun32-gcc toolchain, resulting vdso contains
'jalr t9' instructions in its code and since in vdso case nobody
sets GOT table code crashes when instruction reached. On other hand
observed that when kernel is built mips-poky-linux-gcc toolchain, the
same 'jalr t9' instruction are replaced with PC relative function
calls using 'bal' instructions.

The difference boils down to -mrelax-pic-calls and -mexplicit-relocs
gcc options that gets different default values depending on gcc
target triplets and corresponding binutils. -mrelax-pic-calls got
enabled by default only in mips-poky-linux-gcc case. MIPS binutils
ld relies on R_MIPS_JALR relocation to convert 'jalr t9' into 'bal'
and such relocation is generated only if -mrelax-pic-calls option
is on.

Please note 'jalr t9' conversion to 'bal' can happen only to static
functions. These static PIC calls use mips local GOT entries that
are supposed to be filled with start of DSO value by run-time linker
(missing in VDSO case) and they do not have dynamic relocations.
Global mips GOT entries must have dynamic relocations and they should
be prevented by cmd_vdso_check Makefile rule.

Solution call out -mrelax-pic-calls and -mexplicit-relocs options
explicitly while compiling MIPS vdso code. That would get correct
and consistent between different toolchains behaviour.

Reported-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Victor Kamensky <kamensky@cisco.com>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: richard.purdie@linuxfoundation.org