linux-toradex.git/include/linux/compiler-gcc.h, branch v5.12-rc5

kbuild: check the minimum compiler version in Kconfig

2021-02-16T03:01:32+00:00

Paul Gortmaker reported a regression in the GCC version check. [1]
If you use GCC 4.8, the build breaks before showing the error message
"error Sorry, your version of GCC is too old - please use 4.9 or newer."

I do not want to apply his fix-up since it implies we would not be able
to remove any cc-option test. Anyway, I admit checking the GCC version
in is too late.

Almost at the same time, Linus also suggested to move the compiler
version error to Kconfig time. [2]

I unified the two similar scripts, gcc-version.sh and clang-version.sh
into cc-version.sh. The old scripts invoked the compiler multiple times
(3 times for gcc-version.sh, 4 times for clang-version.sh). I refactored
the code so the new one invokes the compiler just once, and also tried
my best to use shell-builtin commands where possible.

The new script runs faster.

$ time ./scripts/clang-version.sh clang
120000

real 0m0.029s
user 0m0.012s
sys 0m0.021s

$ time ./scripts/cc-version.sh clang
Clang 120000

real 0m0.009s
user 0m0.006s
sys 0m0.004s

cc-version.sh also shows an error message if the compiler is too old:

$ make defconfig CC=clang-9
*** Default configuration is based on 'x86_64_defconfig'
***
*** Compiler is too old.
*** Your Clang version: 9.0.1
*** Minimum Clang version: 10.0.1
***
scripts/Kconfig.include:46: Sorry, this compiler is not supported.
make[1]: *** [scripts/kconfig/Makefile:81: defconfig] Error 1
make: *** [Makefile:602: defconfig] Error 2

The new script takes care of ICC because we have
although I am not sure if building the kernel with ICC is well-supported.

[1]: https://lore.kernel.org/r/20210110190807.134996-1-paul.gortmaker@windriver.com
[2]: https://lore.kernel.org/r/CAHk-=wh-+TMHPTFo1qs-MYyK7tZh-OQovA=pP3=e06aCVp6_kA@mail.gmail.com

Fixes: 87de84c9140e ("kbuild: remove cc-option test of -Werror=date-time")
Reported-by: Paul Gortmaker
Suggested-by: Linus Torvalds
Reviewed-by: Nick Desaulniers
Tested-by: Nick Desaulniers
Reviewed-by: Nathan Chancellor
Tested-by: Nathan Chancellor
Reviewed-by: Miguel Ojeda
Tested-by: Miguel Ojeda
Tested-by: Sedat Dilek
Signed-off-by: Masahiro Yamada

compiler.h: Raise minimum version of GCC to 5.1 for arm64

2021-01-15T10:04:49+00:00

GCC versions >= 4.9 and < 5.1 have been shown to emit memory references
beyond the stack pointer, resulting in memory corruption if an interrupt
is taken after the stack pointer has been adjusted but before the
reference has been executed. This leads to subtle, infrequent data
corruption such as the EXT4 problems reported by Russell King at the
link below.

Life is too short for buggy compilers, so raise the minimum GCC version
required by arm64 to 5.1.

Reported-by: Russell King 
Suggested-by: Arnd Bergmann 
Signed-off-by: Will Deacon 
Tested-by: Nathan Chancellor 
Reviewed-by: Nick Desaulniers 
Reviewed-by: Nathan Chancellor 
Acked-by: Linus Torvalds 
Cc: 
Cc: Theodore Ts'o 
Cc: Florian Weimer 
Cc: Peter Zijlstra 
Cc: Nick Desaulniers 
Link: https://lore.kernel.org/r/20210105154726.GD1551@shell.armlinux.org.uk
Link: https://lore.kernel.org/r/20210112224832.10980-1-will@kernel.org
Signed-off-by: Catalin Marinas

compiler.h: fix barrier_data() on clang

2020-11-14T19:26:03+00:00

Commit 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h
mutually exclusive") neglected to copy barrier_data() from
compiler-gcc.h into compiler-clang.h.

The definition in compiler-gcc.h was really to work around clang's more
aggressive optimization, so this broke barrier_data() on clang, and
consequently memzero_explicit() as well.

For example, this results in at least the memzero_explicit() call in
lib/crypto/sha256.c:sha256_transform() being optimized away by clang.

Fix this by moving the definition of barrier_data() into compiler.h.

Also move the gcc/clang definition of barrier() into compiler.h,
__memory_barrier() is icc-specific (and barrier() is already defined
using it in compiler-intel.h) and doesn't belong in compiler.h.

[rdunlap@infradead.org: fix ALPHA builds when SMP is not enabled]

Link: https://lkml.kernel.org/r/20201101231835.4589-1-rdunlap@infradead.org
Fixes: 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive")
Signed-off-by: Arvind Sankar 
Signed-off-by: Randy Dunlap 
Signed-off-by: Andrew Morton 
Tested-by: Nick Desaulniers 
Reviewed-by: Nick Desaulniers 
Reviewed-by: Kees Cook 
Cc: 
Link: https://lkml.kernel.org/r/20201014212631.207844-1-nivedita@alum.mit.edu
Signed-off-by: Linus Torvalds

bpf: Don't rely on GCC attribute((optimize)) to disable GCSE

2020-10-30T03:01:46+00:00

Commit 3193c0836 ("bpf: Disable GCC -fgcse optimization for
___bpf_prog_run()") introduced a __no_fgcse macro that expands to a
function scope __attribute__((optimize("-fno-gcse"))), to disable a
GCC specific optimization that was causing trouble on x86 builds, and
was not expected to have any positive effect in the first place.

However, as the GCC manual documents, __attribute__((optimize))
is not for production use, and results in all other optimization
options to be forgotten for the function in question. This can
cause all kinds of trouble, but in one particular reported case,
it causes -fno-asynchronous-unwind-tables to be disregarded,
resulting in .eh_frame info to be emitted for the function.

This reverts commit 3193c0836, and instead, it disables the -fgcse
optimization for the entire source file, but only when building for
X86 using GCC with CONFIG_BPF_JIT_ALWAYS_ON disabled. Note that the
original commit states that CONFIG_RETPOLINE=n triggers the issue,
whereas CONFIG_RETPOLINE=y performs better without the optimization,
so it is kept disabled in both cases.

Fixes: 3193c0836f20 ("bpf: Disable GCC -fgcse optimization for ___bpf_prog_run()")
Signed-off-by: Ard Biesheuvel 
Signed-off-by: Alexei Starovoitov 
Tested-by: Geert Uytterhoeven 
Reviewed-by: Nick Desaulniers 
Link: https://lore.kernel.org/lkml/CAMuHMdUg0WJHEcq6to0-eODpXPOywLot6UD2=GFHpzoj_hCoBQ@mail.gmail.com/
Link: https://lore.kernel.org/bpf/20201028171506.15682-2-ardb@kernel.org

compiler-gcc: improve version error

2020-10-14T01:38:26+00:00

As Kees suggests, doing so provides developers with two useful pieces of
information:
- The kernel build was attempting to use GCC.
  (Maybe they accidentally poked the wrong configs in a CI.)
- They need 4.9 or better.
  ("Upgrade to what version?" doesn't need to be dug out of documentation,
   headers, etc.)

Suggested-by: Kees Cook 
Signed-off-by: Nick Desaulniers 
Signed-off-by: Andrew Morton 
Tested-by: Sedat Dilek 
Reviewed-by: Kees Cook 
Reviewed-by: Miguel Ojeda 
Reviewed-by: Nathan Chancellor 
Reviewed-by: Sedat Dilek 
Cc: Andrey Konovalov 
Cc: Fangrui Song 
Cc: Marco Elver 
Cc: Alexei Starovoitov 
Cc: Daniel Borkmann 
Cc: Masahiro Yamada 
Cc: Vincenzo Frascino 
Cc: Will Deacon 
Link: https://lkml.kernel.org/r/20200902225911.209899-8-ndesaulniers@google.com
Signed-off-by: Linus Torvalds

Merge tag 'uninit-macro-v5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

2020-08-04T20:49:43+00:00

Pull uninitialized_var() macro removal from Kees Cook:
 "This is long overdue, and has hidden too many bugs over the years. The
  series has several "by hand" fixes, and then a trivial treewide
  replacement.

   - Clean up non-trivial uses of uninitialized_var()

   - Update documentation and checkpatch for uninitialized_var() removal

   - Treewide removal of uninitialized_var()"

* tag 'uninit-macro-v5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  compiler: Remove uninitialized_var() macro
  treewide: Remove uninitialized_var() usage
  checkpatch: Remove awareness of uninitialized_var() macro
  mm/debug_vm_pgtable: Remove uninitialized_var() usage
  f2fs: Eliminate usage of uninitialized_var() macro
  media: sur40: Remove uninitialized_var() usage
  KVM: PPC: Book3S PR: Remove uninitialized_var() usage
  clk: spear: Remove uninitialized_var() usage
  clk: st: Remove uninitialized_var() usage
  spi: davinci: Remove uninitialized_var() usage
  ide: Remove uninitialized_var() usage
  rtlwifi: rtl8192cu: Remove uninitialized_var() usage
  b43: Remove uninitialized_var() usage
  drbd: Remove uninitialized_var() usage
  x86/mm/numa: Remove uninitialized_var() usage
  docs: deprecated.rst: Add uninitialized_var()

compiler: Remove uninitialized_var() macro

2020-07-16T19:35:31+00:00

Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused variable"). If the compiler thinks it is uninitialized,
either simply initialize the variable or make compiler changes.

As recommended[2] by[3] Linus[4], remove the macro. With the recent
change to disable -Wmaybe-uninitialized in v5.7 in commit 78a5255ffb6a
("Stop the ad-hoc games with -Wno-maybe-initialized"), this is likely
the best time to make this treewide change.

[1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
[2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
[4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Suggested-by: Linus Torvalds 
Reviewed-by: Bart van Assche 
Reviewed-by: Miguel Ojeda 
Tested-by: Nathan Chancellor 
Tested-by: Sedat Dilek 
Signed-off-by: Kees Cook

Raise gcc version requirement to 4.9

2020-07-08T17:48:35+00:00

I realize that we fairly recently raised it to 4.8, but the fact is, 4.9
is a much better minimum version to target.

We have a number of workarounds for actual bugs in pre-4.9 gcc versions
(including things like internal compiler errors on ARM), but we also
have some syntactic workarounds for lacking features.

In particular, raising the minimum to 4.9 means that we can now just
assume _Generic() exists, which is likely the much better replacement
for a lot of very convoluted built-time magic with conditionals on
sizeof and/or __builtin_choose_expr() with same_type() etc.

Using _Generic also means that you will need to have a very recent
version of 'sparse', but thats easy to build yourself, and much less of
a hassle than some old gcc version can be.

The latest (in a long string) of reasons for minimum compiler version
upgrades was commit 5435f73d5c4a ("efi/x86: Fix build with gcc 4").

Ard points out that RHEL 7 uses gcc-4.8, but the people who stay back on
old RHEL versions persumably also don't build their own kernels anyway.
And maybe they should cross-built or just have a little side affair with
a newer compiler?

Acked-by: Ard Biesheuvel 
Acked-by: Peter Zijlstra 
Signed-off-by: Linus Torvalds

compiler_types.h: Add __no_sanitize_{address,undefined} to noinstr

2020-06-15T12:10:09+00:00

Adds the portable definitions for __no_sanitize_address, and
__no_sanitize_undefined, and subsequently changes noinstr to use the
attributes to disable instrumentation via KASAN or UBSAN.

Reported-by: syzbot+dc1fa714cb070b184db5@syzkaller.appspotmail.com
Signed-off-by: Marco Elver 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Miguel Ojeda 
Link: https://lore.kernel.org/lkml/000000000000d2474c05a6c938fe@google.com/

Rebase locking/kcsan to locking/urgent

2020-06-11T18:02:46+00:00

Merge the state of the locking kcsan branch before the read/write_once()
and the atomics modifications got merged.

Squash the fallout of the rebase on top of the read/write once and atomic
fallback work into the merge. The history of the original branch is
preserved in tag locking-kcsan-2020-06-02.

Signed-off-by: Thomas Gleixner