linux-stable.git/include/linux/compiler_types.h, branch v5.3.3

bpf: Disable GCC -fgcse optimization for ___bpf_prog_run()

2019-07-18T19:01:06+00:00

On x86-64, with CONFIG_RETPOLINE=n, GCC's "global common subexpression
elimination" optimization results in ___bpf_prog_run()'s jumptable code
changing from this:

select_insn:
jmp *jumptable(, %rax, 8)
...
ALU64_ADD_X:
...
jmp *jumptable(, %rax, 8)
ALU_ADD_X:
...
jmp *jumptable(, %rax, 8)

to this:

select_insn:
mov jumptable, %r12
jmp *(%r12, %rax, 8)
...
ALU64_ADD_X:
...
jmp *(%r12, %rax, 8)
ALU_ADD_X:
...
jmp *(%r12, %rax, 8)

The jumptable address is placed in a register once, at the beginning of
the function. The function execution can then go through multiple
indirect jumps which rely on that same register value. This has a few
issues:

1) Objtool isn't smart enough to be able to track such a register value
across multiple recursive indirect jumps through the jump table.

2) With CONFIG_RETPOLINE enabled, this optimization actually results in
a small slowdown. I measured a ~4.7% slowdown in the test_bpf
"tcpdump port 22" selftest.

This slowdown is actually predicted by the GCC manual:

Note: When compiling a program using computed gotos, a GCC
extension, you may get better run-time performance if you
disable the global common subexpression elimination pass by
adding -fno-gcse to the command line.

So just disable the optimization for this function.

Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code")
Reported-by: Randy Dunlap
Signed-off-by: Josh Poimboeuf
Signed-off-by: Thomas Gleixner
Acked-by: Alexei Starovoitov
Acked-by: Peter Zijlstra (Intel)
Link: https://lkml.kernel.org/r/30c3ca29ba037afcbd860a8672eef0021addf9fe.1563413318.git.jpoimboe@redhat.com

compiler.h: add CC_USING_PATCHABLE_FUNCTION_ENTRY

2019-06-08T10:56:28+00:00

This can be used for architectures implementing dynamic
ftrace via -fpatchable-function-entry.

Signed-off-by: Sven Schnelle 
Signed-off-by: Helge Deller

compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING

2019-05-15T02:52:48+00:00

Commit 60a3cdd06394 ("x86: add optimized inlining") introduced
CONFIG_OPTIMIZE_INLINING, but it has been available only for x86.

The idea is obviously arch-agnostic.  This commit moves the config entry
from arch/x86/Kconfig.debug to lib/Kconfig.debug so that all
architectures can benefit from it.

This can make a huge difference in kernel image size especially when
CONFIG_OPTIMIZE_FOR_SIZE is enabled.

For example, I got 3.5% smaller arm64 kernel for v5.1-rc1.

  dec       file
  18983424  arch/arm64/boot/Image.before
  18321920  arch/arm64/boot/Image.after

This also slightly improves the "Kernel hacking" Kconfig menu as
e61aca5158a8 ("Merge branch 'kconfig-diet' from Dave Hansen') suggested;
this config option would be a good fit in the "compiler option" menu.

Link: http://lkml.kernel.org/r/20190423034959.13525-12-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada 
Acked-by: Borislav Petkov 
Cc: Arnd Bergmann 
Cc: Benjamin Herrenschmidt 
Cc: Boris Brezillon 
Cc: Brian Norris 
Cc: Christophe Leroy 
Cc: David Woodhouse 
Cc: Heiko Carstens 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Marek Vasut 
Cc: Mark Rutland 
Cc: Mathieu Malaterre 
Cc: Miquel Raynal 
Cc: Paul Mackerras 
Cc: Ralf Baechle 
Cc: Richard Weinberger 
Cc: Russell King 
Cc: Stefan Agner 
Cc: Thomas Gleixner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

include/linux/compiler_types.h: don't pollute userspace with macro definitions

2018-12-14T15:57:16+00:00

Macros 'inline' and '__gnu_inline' used to be defined in compiler-gcc.h,
which was (and is) included entirely in (__KERNEL__ && !__ASSEMBLY__).
Commit 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually
exclusive") had those macros exposed to userspace, unintentionally.

Then commit a3f8a30f3f00 ("Compiler Attributes: use feature checks
instead of version checks") moved '__gnu_inline' back into
(__KERNEL__ && !__ASSEMBLY__) and 'inline' was left behind. Since 'inline'
depends on '__gnu_inline', compiling error showing "unknown type name
‘__gnu_inline’" will pop up, if userspace somehow includes
.

Other macros like __must_check, notrace, etc. are in a similar situation.
So just move all these macros back into (__KERNEL__ && !__ASSEMBLY__).

Note:
  1. This patch only affects what userspace sees.
  2. __must_check (when !CONFIG_ENABLE_MUST_CHECK) and noinline_for_stack
     were once defined in __KERNEL__ only, but we believe that they can
     be put into !__ASSEMBLY__ too.

Acked-by: Nick Desaulniers 
Signed-off-by: Xiaozhou Liu 
Signed-off-by: Miguel Ojeda

include/linux/compiler*.h: define asm_volatile_goto

2018-11-06T14:30:16+00:00

asm_volatile_goto should also be defined for other compilers that support
asm goto.

Fixes commit 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h
mutually exclusive").

Signed-off-by: Nick Desaulniers 
Signed-off-by: Miguel Ojeda

Compiler Attributes: use feature checks instead of version checks

2018-09-30T18:14:03+00:00

Instead of using version checks per-compiler to define (or not)
each attribute, use __has_attribute to test for them, following
the cleanup started with commit 815f0ddb346c
("include/linux/compiler*.h: make compiler-*.h mutually exclusive"),
which is supported on gcc >= 5, clang >= 2.9 and icc >= 17.
In the meantime, to support 4.6 <= gcc < 5, we implement
__has_attribute by hand.

All the attributes that can be unconditionally defined and directly
map to compiler attribute(s) (even if optional) have been moved
to a new file include/linux/compiler_attributes.h

In an effort to make the file as regular as possible, comments
stating the purpose of attributes have been removed. Instead,
links to the compiler docs have been added (i.e. to gcc and,
if available, to clang as well). In addition, they have been sorted.

Finally, if an attribute is optional (i.e. if it is guarded
by __has_attribute), the reason has been stated for future reference.

Tested-by: Sedat Dilek  # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers 
Reviewed-by: Luc Van Oostenryck 
Signed-off-by: Miguel Ojeda

Compiler Attributes: add missing SPDX ID in compiler_types.h

2018-09-30T18:14:03+00:00

Tested-by: Sedat Dilek  # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers 
Reviewed-by: Luc Van Oostenryck 
Signed-off-by: Miguel Ojeda

Compiler Attributes: remove unneeded sparse (CHECKER) tests

2018-09-30T18:14:03+00:00

Sparse knows about a few more attributes now, so we can remove
the __CHECKER__ conditions from them (which, in turn, allow us
to move some of them later on to compiler_attributes.h).

  * assume_aligned: since sparse's commit ffc860b ("sparse:
    ignore __assume_aligned__ attribute"), included in 0.5.1

  * error: since sparse's commit 0a04210 ("sparse: Add 'error'
    to ignored attributes"), included in 0.5.0

  * hotpatch: since sparse's commit 6043210 ("sparse/parse.c:
    ignore hotpatch attribute"), included in 0.5.1

  * warning: since sparse's commit 977365d ("Avoid "attribute
    'warning': unknown attribute" warning"), included in 0.4.2

On top of that, __must_be_array does not need it either because:

  * Even ancient versions of sparse do not have a problem

  * BUILD_BUG_ON_ZERO() is currently disabled for __CHECKER__

Tested-by: Sedat Dilek  # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers 
Reviewed-by: Luc Van Oostenryck 
Signed-off-by: Miguel Ojeda

Compiler Attributes: remove unneeded tests

2018-09-30T18:14:03+00:00

Attributes const and always_inline have tests around them
which are unneeded, since they are supported by gcc >= 4.6,
clang >= 3 and icc >= 13. https://godbolt.org/z/DFPq37

In the case of gnu_inline, we do not need to test for
__GNUC_STDC_INLINE__ because, regardless of the current
inlining behavior, we can simply always force the old
GCC inlining behavior by using the attribute in all cases.

Tested-by: Sedat Dilek  # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers 
Reviewed-by: Luc Van Oostenryck 
Signed-off-by: Miguel Ojeda

Compiler Attributes: always use the extra-underscores syntax

2018-09-30T18:14:03+00:00

The attribute syntax optionally allows to surround attribute names
with "__" in order to avoid collisions with macros of the same name
(see https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html).

This homogenizes all attributes to use the syntax with underscores.
While there are currently only a handful of cases of some TUs defining
macros like "error" which may collide with the attributes,
this should prevent futures surprises.

This has been done only for "standard" attributes supported by
the major compilers. In other words, those of third-party tools
(e.g. sparse, plugins...) have not been changed for the moment.

Tested-by: Sedat Dilek  # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers 
Reviewed-by: Luc Van Oostenryck 
Signed-off-by: Miguel Ojeda

linux-stable.git/include/linux/compiler_types.h, branch v5.3.3

bpf: Disable GCC -fgcse optimization for ___bpf_prog_run()

compiler.h: add CC_USING_PATCHABLE_FUNCTION_ENTRY

compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING

include/linux/compiler_types.h: don't pollute userspace with macro definitions

include/linux/compiler*.h: define asm_volatile_goto

Compiler Attributes: use feature checks instead of version checks

Compiler Attributes: add missing SPDX ID in compiler_types.h

Compiler Attributes: remove unneeded sparse (__CHECKER__) tests

Compiler Attributes: remove unneeded tests

Compiler Attributes: always use the extra-underscores syntax

Compiler Attributes: remove unneeded sparse (CHECKER) tests