linux-stable.git/include/linux/compiler-gcc.h, branch v6.8.4

update workarounds for gcc "asm goto" issue

2024-02-15T19:14:33+00:00

In commit 4356e9f841f7 ("work around gcc bugs with 'asm goto' with
outputs") I did the gcc workaround unconditionally, because the cause of
the bad code generation wasn't entirely clear.

In the meantime, Jakub Jelinek debugged the issue, and has come up with
a fix in gcc [2], which also got backported to the still maintained
branches of gcc-11, gcc-12 and gcc-13.

Note that while the fix technically wasn't in the original gcc-14
branch, Jakub says:

 "while it is true that no GCC 14 snapshots until today (or whenever the
  fix will be committed) have the fix, for GCC trunk it is up to the
  distros to use the latest snapshot if they use it at all and would
  allow better testing of the kernel code without the workaround, so
  that if there are other issues they won't be discovered years later.
  Most userland code doesn't actually use asm goto with outputs..."

so we will consider gcc-14 to be fixed - if somebody is using gcc
snapshots of the gcc-14 before the fix, they should upgrade.

Note that while the bug goes back to gcc-11, in practice other gcc
changes seem to have effectively hidden it since gcc-12.1 as per a
bisect by Jakub.  So even a gcc-14 snapshot without the fix likely
doesn't show actual problems.

Also, make the default 'asm_goto_output()' macro mark the asm as
volatile by hand, because of an unrelated gcc issue [1] where it doesn't
match the documented behavior ("asm goto is always volatile").

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103979 [1]
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921 [2]
Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/
Requested-by: Jakub Jelinek 
Cc: Uros Bizjak 
Cc: Nick Desaulniers 
Cc: Sean Christopherson 
Cc: Andrew Pinski 
Signed-off-by: Linus Torvalds

work around gcc bugs with 'asm goto' with outputs

2024-02-09T23:57:48+00:00

We've had issues with gcc and 'asm goto' before, and we created a
'asm_volatile_goto()' macro for that in the past: see commits
3f0116c3238a ("compiler/gcc4: Add quirk for 'asm goto' miscompilation
bug") and a9f180345f53 ("compiler/gcc4: Make quirk for
asm_volatile_goto() unconditional").

Then, much later, we ended up removing the workaround in commit
43c249ea0b1e ("compiler-gcc.h: remove ancient workaround for gcc PR
58670") because we no longer supported building the kernel with the
affected gcc versions, but we left the macro uses around.

Now, Sean Christopherson reports a new version of a very similar
problem, which is fixed by re-applying that ancient workaround.  But the
problem in question is limited to only the 'asm goto with outputs'
cases, so instead of re-introducing the old workaround as-is, let's
rename and limit the workaround to just that much less common case.

It looks like there are at least two separate issues that all hit in
this area:

 (a) some versions of gcc don't mark the asm goto as 'volatile' when it
     has outputs:

        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98619
        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110420

     which is easy to work around by just adding the 'volatile' by hand.

 (b) Internal compiler errors:

        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110422

     which are worked around by adding the extra empty 'asm' as a
     barrier, as in the original workaround.

but the problem Sean sees may be a third thing since it involves bad
code generation (not an ICE) even with the manually added 'volatile'.

but the same old workaround works for this case, even if this feels a
bit like voodoo programming and may only be hiding the issue.

Reported-and-tested-by: Sean Christopherson 
Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/
Cc: Nick Desaulniers 
Cc: Uros Bizjak 
Cc: Jakub Jelinek 
Cc: Andrew Pinski 
Signed-off-by: Linus Torvalds

compiler-gcc: Suppress -Wmissing-prototypes warning for all supported GCC

2023-11-10T15:53:19+00:00

The kernel supports a minimum GCC version of 5.1.0 for building. However,
the "__diag_ignore_all" directive only suppresses the
"-Wmissing-prototypes" warning for GCC versions >= 8.0.0. As a result, when
building the kernel with older GCC versions, warnings may be triggered. The
example below illustrates the warnings reported by the kernel test robot
using GCC 7.5.0:

  compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
  All warnings (new ones prefixed by >>):

   kernel/bpf/helpers.c:1893:19: warning: no previous prototype for 'bpf_obj_new_impl' [-Wmissing-prototypes]
    __bpf_kfunc void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign)
                      ^~~~~~~~~~~~~~~~
   kernel/bpf/helpers.c:1907:19: warning: no previous prototype for 'bpf_percpu_obj_new_impl' [-Wmissing-prototypes]
    __bpf_kfunc void *bpf_percpu_obj_new_impl(u64 local_type_id__k, void *meta__ign)
   [...]

To address this, we should also suppress the "-Wmissing-prototypes" warning
for older GCC versions. "#pragma GCC diagnostic push" is supported as
of GCC 4.6, and both "-Wmissing-prototypes" and "-Wmissing-declarations"
are supported for all the GCC versions that we currently support.
Therefore, it is reasonable to suppress these warnings for all supported
GCC versions.

With this adjustment, it's important to note that after implementing
"__diag_ignore_all", it will effectively suppress warnings for all the
supported GCC versions.

In the future, if you wish to suppress warnings that are only supported on
higher GCC versions, it is advisable to explicitly use "__diag_ignore" to
specify the GCC version you are targeting.

Reported-by: kernel test robot 
Closes: https://lore.kernel.org/oe-kbuild-all/202311031651.A7crZEur-lkp@intel.com/
Suggested-by: Arnd Bergmann 
Signed-off-by: Yafang Shao 
Cc: Kumar Kartikeya Dwivedi 
Cc: Arnd Bergmann 
Acked-by: Arnd Bergmann 
Link: https://lore.kernel.org/r/20231106031802.4188-1-laoar.shao@gmail.com
Signed-off-by: Alexei Starovoitov

compiler.h: unify __UNIQUE_ID

2023-10-04T17:41:56+00:00

commit 6f33d58794ef ("__UNIQUE_ID()")
added a fallback definition of __UNIQUE_ID because gcc 4.2 and older did
not support __COUNTER__.

Also, this commit is effectively a revert of
commit b41c29b0527c ("Kbuild: provide a __UNIQUE_ID for clang")
which mentions clang 2.6+ supporting __COUNTER__.

Documentation/process/changes.rst currently lists the minimum supported
version of these compilers as:
- gcc: 5.1
- clang: 11.0.0
It should be safe to say that __COUNTER__ is well supported by this
point.

Link: https://lkml.kernel.org/r/20230831-unique_id-v1-1-28bacd18eb1d@google.com
Signed-off-by: Nick Desaulniers 
Cc: Arnd Bergmann 
Cc: Jan Beulich 
Cc: Luc Van Oostenryck 
Cc: Michal rarek 
Cc: Nathan Chancellor 
Cc: Paul Russel 
Cc: Tom Rix 
Signed-off-by: Andrew Morton

compiler-gcc: document minimum version for `__no_sanitize_coverage__`

2022-11-09T01:37:20+00:00

The attribute was added in GCC 12.1.

This will simplify future cleanups, and is closer to what we do
in `compiler_attributes.h`.

Link: https://godbolt.org/z/MGbT76j6G
Link: https://lkml.kernel.org/r/20221021115956.9947-5-ojeda@kernel.org
Signed-off-by: Miguel Ojeda 
Acked-by: Marco Elver 
Reviewed-by: Nathan Chancellor 
Cc: Alexander Potapenko 
Cc: Andrey Konovalov 
Cc: Arnd Bergmann 
Cc: Dan Li 
Cc: Kees Cook 
Cc: Kumar Kartikeya Dwivedi 
Cc: Nick Desaulniers 
Cc: Uros Bizjak 
Signed-off-by: Andrew Morton

compiler-gcc: remove attribute support check for `__no_sanitize_undefined__`

2022-11-09T01:37:20+00:00

The attribute was added in GCC 4.9, while the minimum GCC version
supported by the kernel is GCC 5.1.

Therefore, remove the check.

Link: https://godbolt.org/z/GrMeo6fYr
Link: https://lkml.kernel.org/r/20221021115956.9947-4-ojeda@kernel.org
Signed-off-by: Miguel Ojeda 
Reviewed-by: Nathan Chancellor 
Cc: Alexander Potapenko 
Cc: Andrey Konovalov 
Cc: Arnd Bergmann 
Cc: Dan Li 
Cc: Kees Cook 
Cc: Kumar Kartikeya Dwivedi 
Cc: Marco Elver 
Cc: Nick Desaulniers 
Cc: Uros Bizjak 
Signed-off-by: Andrew Morton

compiler-gcc: remove attribute support check for `__no_sanitize_thread__`

2022-11-09T01:37:20+00:00

The attribute was added in GCC 5.1, which matches the minimum GCC version
supported by the kernel.

Therefore, remove the check.

Link: https://godbolt.org/z/vbxKejxbx
Link: https://lkml.kernel.org/r/20221021115956.9947-3-ojeda@kernel.org
Signed-off-by: Miguel Ojeda 
Acked-by: Marco Elver 
Reviewed-by: Nathan Chancellor 
Cc: Alexander Potapenko 
Cc: Andrey Konovalov 
Cc: Arnd Bergmann 
Cc: Dan Li 
Cc: Kees Cook 
Cc: Kumar Kartikeya Dwivedi 
Cc: Nick Desaulniers 
Cc: Uros Bizjak 
Signed-off-by: Andrew Morton

compiler-gcc: remove attribute support check for `__no_sanitize_address__`

2022-11-09T01:37:20+00:00

The attribute was added in GCC 4.8, while the minimum GCC version
supported by the kernel is GCC 5.1.

Therefore, remove the check.

Link: https://godbolt.org/z/84v56vcn8
Link: https://lkml.kernel.org/r/20221021115956.9947-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda 
Reviewed-by: Nathan Chancellor 
Cc: Alexander Potapenko 
Cc: Andrey Konovalov 
Cc: Arnd Bergmann 
Cc: Dan Li 
Cc: Kees Cook 
Cc: Kumar Kartikeya Dwivedi 
Cc: Marco Elver 
Cc: Nick Desaulniers 
Cc: Uros Bizjak 
Signed-off-by: Andrew Morton

compiler-gcc: be consistent with underscores use for `no_sanitize`

2022-11-09T01:37:20+00:00

Patch series "compiler-gcc: be consistent with underscores use for
`no_sanitize`".


This patch (of 5):

Other macros that define shorthands for attributes in e.g. 
`compiler_attributes.h` and elsewhere use underscores.

Link: https://lkml.kernel.org/r/20221021115956.9947-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda 
Reviewed-by: Nathan Chancellor 
Cc: Marco Elver 
Cc: Alexander Potapenko 
Cc: Andrey Konovalov 
Cc: Arnd Bergmann 
Cc: Dan Li 
Cc: Kees Cook 
Cc: Kumar Kartikeya Dwivedi 
Cc: Nick Desaulniers 
Cc: Uros Bizjak 
Signed-off-by: Andrew Morton

kmsan: introduce __no_sanitize_memory and __no_kmsan_checks

2022-10-03T21:03:19+00:00

__no_sanitize_memory is a function attribute that instructs KMSAN to skip
a function during instrumentation.  This is needed to e.g.  implement the
noinstr functions.

__no_kmsan_checks is a function attribute that makes KMSAN ignore the
uninitialized values coming from the function's inputs, and initialize the
function's outputs.

Functions marked with this attribute can't be inlined into functions not
marked with it, and vice versa.  This behavior is overridden by
__always_inline.

__SANITIZE_MEMORY__ is a macro that's defined iff the file is instrumented
with KMSAN.  This is not the same as CONFIG_KMSAN, which is defined for
every file.

Link: https://lkml.kernel.org/r/20220915150417.722975-8-glider@google.com
Signed-off-by: Alexander Potapenko 
Reviewed-by: Marco Elver 
Cc: Alexander Viro 
Cc: Alexei Starovoitov 
Cc: Andrey Konovalov 
Cc: Andrey Konovalov 
Cc: Andy Lutomirski 
Cc: Arnd Bergmann 
Cc: Borislav Petkov 
Cc: Christoph Hellwig 
Cc: Christoph Lameter 
Cc: David Rientjes 
Cc: Dmitry Vyukov 
Cc: Eric Biggers 
Cc: Eric Biggers 
Cc: Eric Dumazet 
Cc: Greg Kroah-Hartman 
Cc: Herbert Xu 
Cc: Ilya Leoshkevich 
Cc: Ingo Molnar 
Cc: Jens Axboe 
Cc: Joonsoo Kim 
Cc: Kees Cook 
Cc: Mark Rutland 
Cc: Matthew Wilcox 
Cc: Michael S. Tsirkin 
Cc: Pekka Enberg 
Cc: Peter Zijlstra 
Cc: Petr Mladek 
Cc: Stephen Rothwell 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Vasily Gorbik 
Cc: Vegard Nossum 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton