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Date: Wed, 19 Dec 2018 12:20:28 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc: x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H . Peter Anvin" <hpa@...or.com>,
Richard Biener <rguenther@...e.de>,
Segher Boessenkool <segher@...nel.crashing.org>,
Peter Zijlstra <peterz@...radead.org>,
Juergen Gross <jgross@...e.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Kees Cook <keescook@...omium.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Arnd Bergmann <arnd@...db.de>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
virtualization@...ts.linux-foundation.org,
Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
Alok Kataria <akataria@...are.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Jann Horn <jannh@...gle.com>, linux-arch@...r.kernel.org,
Alexey Dobriyan <adobriyan@...il.com>,
linux-sparse@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kbuild@...r.kernel.org, Yonghong Song <yhs@...com>,
Michal Marek <michal.lkml@...kovi.net>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Jan Beulich <JBeulich@...e.com>, Nadav Amit <namit@...are.com>,
David Woodhouse <dwmw@...zon.co.uk>,
Alexei Starovoitov <ast@...nel.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/12] x86, kbuild: revert macrofying inline assembly
code
* Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
> This series reverts the in-kernel workarounds for inlining issues.
>
> The commit description of 77b0bf55bc67 mentioned
> "We also hope that GCC will eventually get fixed,..."
>
> Now, GCC provides a solution.
>
> https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
> explains the new "asm inline" syntax.
>
> The performance issue will be eventually solved.
>
> [About Code cleanups]
>
> I know Nadam Amit is opposed to the full revert.
> He also claims his motivation for macrofying was not only
> performance, but also cleanups.
>
> IIUC, the criticism addresses the code duplication between C and ASM.
>
> If so, I'd like to suggest a different approach for cleanups.
> Please see the last 3 patches.
> IMHO, preprocessor approach is more straight-forward, and readable.
> Basically, this idea should work because it is what we already do for
> __ASM_FORM() etc.
>
> [Quick Test of "asm inline" of GCC 9]
>
> If you want to try "asm inline" feature, the patch is available:
> https://lore.kernel.org/patchwork/patch/1024590/
>
> The number of symbols for arch/x86/configs/x86_64_defconfig:
>
> nr_symbols
> [1] v4.20-rc7 : 96502
> [2] [1]+full revert : 96705 (+203)
> [3] [2]+"asm inline": 96568 (-137)
>
> [3]: apply my patch, then replace "asm" -> "asm_inline"
> for _BUG_FLAGS(), refcount_add(), refcount_inc(), refcount_dec(),
> annotate_reachable(), annotate_unreachable()
>
>
> Changes in v3:
> - Split into per-commit revert (per Nadav Amit)
> - Add some cleanups with preprocessor approach
>
> Changes in v2:
> - Revive clean-ups made by 5bdcd510c2ac (per Peter Zijlstra)
> - Fix commit quoting style (per Peter Zijlstra)
>
> Masahiro Yamada (12):
> Revert "x86/jump-labels: Macrofy inline assembly code to work around
> GCC inlining bugs"
> Revert "x86/cpufeature: Macrofy inline assembly code to work around
> GCC inlining bugs"
> Revert "x86/extable: Macrofy inline assembly code to work around GCC
> inlining bugs"
> Revert "x86/paravirt: Work around GCC inlining bugs when compiling
> paravirt ops"
> Revert "x86/bug: Macrofy the BUG table section handling, to work
> around GCC inlining bugs"
> Revert "x86/alternatives: Macrofy lock prefixes to work around GCC
> inlining bugs"
> Revert "x86/refcount: Work around GCC inlining bug"
> Revert "x86/objtool: Use asm macros to work around GCC inlining bugs"
> Revert "kbuild/Makefile: Prepare for using macros in inline assembly
> code to work around asm() related GCC inlining bugs"
> linux/linkage: add ASM() macro to reduce duplication between C/ASM
> code
> x86/alternatives: consolidate LOCK_PREFIX macro
> x86/asm: consolidate ASM_EXTABLE_* macros
>
> Makefile | 9 +--
> arch/x86/Makefile | 7 ---
> arch/x86/include/asm/alternative-asm.h | 22 +------
> arch/x86/include/asm/alternative-common.h | 47 +++++++++++++++
> arch/x86/include/asm/alternative.h | 30 +---------
> arch/x86/include/asm/asm.h | 46 +++++----------
> arch/x86/include/asm/bug.h | 98 +++++++++++++------------------
> arch/x86/include/asm/cpufeature.h | 82 +++++++++++---------------
> arch/x86/include/asm/jump_label.h | 22 +++++--
> arch/x86/include/asm/paravirt_types.h | 56 +++++++++---------
> arch/x86/include/asm/refcount.h | 81 +++++++++++--------------
> arch/x86/kernel/macros.S | 16 -----
> include/asm-generic/bug.h | 8 +--
> include/linux/compiler.h | 56 ++++--------------
> include/linux/linkage.h | 8 +++
> scripts/Kbuild.include | 4 +-
> scripts/mod/Makefile | 2 -
> 17 files changed, 249 insertions(+), 345 deletions(-)
> create mode 100644 arch/x86/include/asm/alternative-common.h
> delete mode 100644 arch/x86/kernel/macros.S
I absolutely agree that this needs to be resolved in v4.20.
So I did the 1-9 reverts manually myself as well, because I think the
first commit should be reverted fully to get as close to the starting
point as possible (we are late in the cycle) - and came to the attached
interdiff between your series and mine.
Does this approach look OK to you, or did I miss something?
Thanks,
Ingo
=============>
entry/calling.h | 2 -
include/asm/jump_label.h | 50 ++++++++++++++++++++++++++++++++++-------------
2 files changed, 38 insertions(+), 14 deletions(-)
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 25e5a6bda8c3..20d0885b00fb 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -352,7 +352,7 @@ For 32-bit we have the following conventions - kernel is built with
.macro CALL_enter_from_user_mode
#ifdef CONFIG_CONTEXT_TRACKING
#ifdef HAVE_JUMP_LABEL
- STATIC_BRANCH_JMP l_yes=.Lafter_call_\@, key=context_tracking_enabled, branch=1
+ STATIC_JUMP_IF_FALSE .Lafter_call_\@, context_tracking_enabled, def=0
#endif
call enter_from_user_mode
.Lafter_call_\@:
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index cf88ebf9a4ca..21efc9d07ed9 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -2,6 +2,19 @@
#ifndef _ASM_X86_JUMP_LABEL_H
#define _ASM_X86_JUMP_LABEL_H
+#ifndef HAVE_JUMP_LABEL
+/*
+ * For better or for worse, if jump labels (the gcc extension) are missing,
+ * then the entire static branch patching infrastructure is compiled out.
+ * If that happens, the code in here will malfunction. Raise a compiler
+ * error instead.
+ *
+ * In theory, jump labels and the static branch patching infrastructure
+ * could be decoupled to fix this.
+ */
+#error asm/jump_label.h included on a non-jump-label kernel
+#endif
+
#define JUMP_LABEL_NOP_SIZE 5
#ifdef CONFIG_X86_64
@@ -53,26 +66,37 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
#else /* __ASSEMBLY__ */
-.macro STATIC_BRANCH_NOP l_yes:req key:req branch:req
-.Lstatic_branch_nop_\@:
- .byte STATIC_KEY_INIT_NOP
-.Lstatic_branch_no_after_\@:
+.macro STATIC_JUMP_IF_TRUE target, key, def
+.Lstatic_jump_\@:
+ .if \def
+ /* Equivalent to "jmp.d32 \target" */
+ .byte 0xe9
+ .long \target - .Lstatic_jump_after_\@
+.Lstatic_jump_after_\@:
+ .else
+ .byte STATIC_KEY_INIT_NOP
+ .endif
.pushsection __jump_table, "aw"
_ASM_ALIGN
- .long .Lstatic_branch_nop_\@ - ., \l_yes - .
- _ASM_PTR \key + \branch - .
+ .long .Lstatic_jump_\@ - ., \target - .
+ _ASM_PTR \key - .
.popsection
.endm
-.macro STATIC_BRANCH_JMP l_yes:req key:req branch:req
-.Lstatic_branch_jmp_\@:
- .byte 0xe9
- .long \l_yes - .Lstatic_branch_jmp_after_\@
-.Lstatic_branch_jmp_after_\@:
+.macro STATIC_JUMP_IF_FALSE target, key, def
+.Lstatic_jump_\@:
+ .if \def
+ .byte STATIC_KEY_INIT_NOP
+ .else
+ /* Equivalent to "jmp.d32 \target" */
+ .byte 0xe9
+ .long \target - .Lstatic_jump_after_\@
+.Lstatic_jump_after_\@:
+ .endif
.pushsection __jump_table, "aw"
_ASM_ALIGN
- .long .Lstatic_branch_jmp_\@ - ., \l_yes - .
- _ASM_PTR \key + \branch - .
+ .long .Lstatic_jump_\@ - ., \target - .
+ _ASM_PTR \key + 1 - .
.popsection
.endm
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