kernel.git/arch/x86/Makefile, branch linux-4.20.y

Revert "kbuild/Makefile: Prepare for using macros in inline assembly code to work around asm() related GCC inlining bugs"

2018-12-19T11:00:28Z

This reverts commit 77b0bf55bc675233d22cd5df97605d516d64525e. See this commit for details about the revert: e769742d3584 ("Revert "x86/jump-labels: Macrofy inline assembly code to work around GCC inlining bugs"") Conflicts: arch/x86/Makefile Reported-by: Masahiro Yamada Reviewed-by: Borislav Petkov Reviewed-by: Thomas Gleixner Cc: Juergen Gross Cc: Richard Biener Cc: Kees Cook Cc: Segher Boessenkool Cc: Ard Biesheuvel Cc: Peter Zijlstra Cc: Josh Poimboeuf Cc: Nadav Amit Cc: Linus Torvalds Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

x86/build: Fix compiler support check for CONFIG_RETPOLINE

2018-12-05T07:44:02Z

It is troublesome to add a diagnostic like this to the Makefile parse stage because the top-level Makefile could be parsed with a stale include/config/auto.conf. Once you are hit by the error about non-retpoline compiler, the compilation still breaks even after disabling CONFIG_RETPOLINE. The easiest fix is to move this check to the "archprepare" like this commit did: 829fe4aa9ac1 ("x86: Allow generating user-space headers without a compiler") Reported-by: Meelis Roos Tested-by: Meelis Roos Signed-off-by: Masahiro Yamada Acked-by: Zhenzhong Duan Cc: Borislav Petkov Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Zhenzhong Duan Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support") Link: http://lkml.kernel.org/r/1543991239-18476-1-git-send-email-yamada.masahiro@socionext.com Link: https://lkml.org/lkml/2018/12/4/206 Signed-off-by: Ingo Molnar

x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support

2018-11-28T10:57:03Z

Since retpoline capable compilers are widely available, make CONFIG_RETPOLINE hard depend on the compiler capability. Break the build when CONFIG_RETPOLINE is enabled and the compiler does not support it. Emit an error message in that case: "arch/x86/Makefile:226: *** You are building kernel with non-retpoline compiler, please update your compiler.. Stop." [dwmw: Fail the build with non-retpoline compiler] Suggested-by: Peter Zijlstra Signed-off-by: Zhenzhong Duan Signed-off-by: Thomas Gleixner Cc: David Woodhouse Cc: Borislav Petkov Cc: Daniel Borkmann Cc: H. Peter Anvin Cc: Konrad Rzeszutek Wilk Cc: Andy Lutomirski Cc: Masahiro Yamada Cc: Michal Marek Cc: Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/cca0cb20-f9e2-4094-840b-fb0f8810cd34@default

x86/build: Remove -pipe from KBUILD_CFLAGS

2018-11-05T15:45:32Z

Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in inline assembly code to work around asm() related GCC inlining bugs") added -Wa,- to KBUILD_CFLAGS, which breaks compiling with Clang (hangs indefinitely at compiling init/main.o). This happens because while Clang accepts -pipe (and has it documented in its list of supported flags), it silently ignores it after this 2010 commit (thanks to Nick Desaulniers for tracking this down), meaning that gas just infinitely waits for stdin and never receives it. https://github.com/llvm-mirror/clang/commit/c19a12dc3d441bec62eed55e312b76c12d6d9022 Initially, I had suggested just add -Wa,- to KBUILD_CFLAGS when GCC was being used but that was before realizing it is because Clang doesn't do anything with -pipe. H. Peter Anvin suggested checking to see if -pipe gives us any gains out of GCC. Turns out it might actually be hurting: With -pipe: real 3m40.813s real 3m44.449s real 3m39.648s Without -pipe: real 3m38.492s real 3m38.335s real 3m38.975s The issue of -Wa,- being passed along to gas without -pipe being supported should still probably be fixed on the LLVM side (open issue: https://bugs.llvm.org/show_bug.cgi?id=39410) but this is not as much of a workaround anymore since it helps both GCC and Clang. Suggested-by: H. Peter Anvin Signed-off-by: Nathan Chancellor Signed-off-by: Thomas Gleixner Tested-by: Nick Desaulniers Reviewed-by: Nadav Amit Reviewed-by: Nick Desaulniers Cc: Borislav Petkov Cc: Kees Cook Cc: Masahiro Yamada Link: https://github.com/ClangBuiltLinux/linux/issues/213 Link: https://lkml.kernel.org/r/20181023231125.27976-1-natechancellor@gmail.com

kbuild/Makefile: Prepare for using macros in inline assembly code to work around asm() related GCC inlining bugs

2018-10-04T08:57:09Z

Using macros in inline assembly allows us to work around bugs in GCC's inlining decisions. Compile macros.S and use it to assemble all C files. Currently only x86 will use it. Background: The inlining pass of GCC doesn't include an assembler, so it's not aware of basic properties of the generated code, such as its size in bytes, or that there are such things as discontiuous blocks of code and data due to the newfangled linker feature called 'sections' ... Instead GCC uses a lazy and fragile heuristic: it does a linear count of certain syntactic and whitespace elements in inlined assembly block source code, such as a count of new-lines and semicolons (!), as a poor substitute for "code size and complexity". Unsurprisingly this heuristic falls over and breaks its neck whith certain common types of kernel code that use inline assembly, such as the frequent practice of putting useful information into alternative sections. As a result of this fresh, 20+ years old GCC bug, GCC's inlining decisions are effectively disabled for inlined functions that make use of such asm() blocks, because GCC thinks those sections of code are "large" - when in reality they are often result in just a very low number of machine instructions. This absolute lack of inlining provess when GCC comes across such asm() blocks both increases generated kernel code size and causes performance overhead, which is particularly noticeable on paravirt kernels, which make frequent use of these inlining facilities in attempt to stay out of the way when running on baremetal hardware. Instead of fixing the compiler we use a workaround: we set an assembly macro and call it from the inlined assembly block. As a result GCC considers the inline assembly block as a single instruction. (Which it often isn't but I digress.) This uglifies and bloats the source code - for example just the refcount related changes have this impact: Makefile | 9 +++++++-- arch/x86/Makefile | 7 +++++++ arch/x86/kernel/macros.S | 7 +++++++ scripts/Kbuild.include | 4 +++- scripts/mod/Makefile | 2 ++ 5 files changed, 26 insertions(+), 3 deletions(-) Yay readability and maintainability, it's not like assembly code is hard to read and maintain ... We also hope that GCC will eventually get fixed, but we are not holding our breath for that. Yet we are optimistic, it might still happen, any decade now. [ mingo: Wrote new changelog describing the background. ] Tested-by: Kees Cook Signed-off-by: Nadav Amit Acked-by: Masahiro Yamada Acked-by: Peter Zijlstra (Intel) Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Michal Marek Cc: Peter Zijlstra Cc: Sam Ravnborg Cc: Thomas Gleixner Cc: linux-kbuild@vger.kernel.org Link: http://lkml.kernel.org/r/20181003213100.189959-3-namit@vmware.com Signed-off-by: Ingo Molnar

x86/build: Remove unused CONFIG_AS_CRC32

2018-10-01T12:58:09Z

CONFIG_AS_CRC32 is not used anywhere. Its last user was removed by 0cb6c969ed9d ("net, lib: kill arch_fast_hash library bits") Signed-off-by: Masahiro Yamada Signed-off-by: Borislav Petkov Cc: Ingo Molnar Cc: Thomas Gleixner Cc: "H. Peter Anvin" Link: https://lkml.kernel.org/r/1538389443-28514-1-git-send-email-yamada.masahiro@socionext.com

x86: Allow generating user-space headers without a compiler

2018-08-31T15:08:22Z

When bootstrapping an architecture, it's usual to generate the kernel's user-space headers (make headers_install) before building a compiler. Move the compiler check (for asm goto support) to the archprepare target so that it is only done when building code for the target. Fixes: e501ce957a78 ("x86: Force asm-goto") Reported-by: Helmut Grohne Signed-off-by: Ben Hutchings Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20180829194317.GA4765@decadent.org.uk

x86/build: Remove jump label quirk for GCC older than 4.5.2

2018-08-30T09:37:08Z

Commit cafa0010cd51 ("Raise the minimum required gcc version to 4.6") bumped the minimum GCC version to 4.6 for all architectures. Remove the workaround code. It was the only user of cc-if-fullversion. Remove the macro as well. Signed-off-by: Masahiro Yamada Signed-off-by: Thomas Gleixner Cc: "H. Peter Anvin" Cc: Michal Marek Cc: linux-kbuild@vger.kernel.org Link: https://lkml.kernel.org/r/1535348714-25457-1-git-send-email-yamada.masahiro@socionext.com

kbuild: rename LDFLAGS to KBUILD_LDFLAGS

2018-08-23T23:22:08Z

Commit a0f97e06a43c ("kbuild: enable 'make CFLAGS=...' to add additional options to CC") renamed CFLAGS to KBUILD_CFLAGS. Commit 222d394d30e7 ("kbuild: enable 'make AFLAGS=...' to add additional options to AS") renamed AFLAGS to KBUILD_AFLAGS. Commit 06c5040cdb13 ("kbuild: enable 'make CPPFLAGS=...' to add additional options to CPP") renamed CPPFLAGS to KBUILD_CPPFLAGS. For some reason, LDFLAGS was not renamed. Using a well-known variable like LDFLAGS may result in accidental override of the variable. Kbuild generally uses KBUILD_ prefixed variables for the internally appended options, so here is one more conversion to sanitize the naming convention. I did not touch Makefiles under tools/ since the tools build system is a different world. Signed-off-by: Masahiro Yamada Acked-by: Kirill A. Shutemov Reviewed-by: Palmer Dabbelt

x86/build: Remove old -funit-at-a-time GCC quirk

2018-07-15T22:25:10Z

The following commit: e501ce957a78 ("x86: Force asm-goto") ... bumped the minimum GCC version to 4.5 for building the x86 kernel. arch/x86/Makefile no longer needs to take care of older GCC versions, such as this pre-4.0 -funit-at-a-time quirk. Signed-off-by: Masahiro Yamada Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: "H. Peter Anvin" Link: http://lkml.kernel.org/r/1531138041-24200-1-git-send-email-yamada.masahiro@socionext.com Signed-off-by: Ingo Molnar