linux-kernel - [PATCH v3 0/6] make use of gcc 9's "asm inline()"

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Message-Id: <20190912221927.18641-1-linux@rasmusvillemoes.dk>
Date:   Fri, 13 Sep 2019 00:19:21 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        ndesaulniers@...gle.com,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nadav Amit <namit@...are.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH v3 0/6] make use of gcc 9's "asm inline()"

gcc 9+ (and gcc 8.3, 7.5) provides a way to override the otherwise
crude heuristic that gcc uses to estimate the size of the code
represented by an asm() statement. From the gcc docs

  If you use 'asm inline' instead of just 'asm', then for inlining
  purposes the size of the asm is taken as the minimum size, ignoring
  how many instructions GCC thinks it is.

For compatibility with older compilers, we obviously want a

  #if [understands asm inline]
  #define asm_inline asm inline
  #else
  #define asm_inline asm
  #endif

But since we #define the identifier inline to attach some attributes,
we have to use an alternate spelling of that keyword. gcc provides
both __inline__ and __inline, and we currently #define both to inline,
so they all have the same semantics. We have to free up one of
__inline__ and __inline, and the latter is by far the easiest. 

The two x86 changes cause smaller code gen differences than I'd
expect, but I think we do want the asm_inline thing available sooner
or later, so this is just to get the ball rolling.

Changes since v1: __inline instead of __inline__, making the diffstat
400 lines smaller.

Changes since v2: Check support of "asm inline" in Kconfig rather than
based on gcc version, since the feature was backported to gcc 7.x and
gcc 8.x. That also automatically enables it if and when Clang grows
support, though that compiler apparently does not have the same
problems with overestimating sizes of asm()s that gcc has.

Patch 1 has already been picked up by Greg in staging-next, it's
included here for completeness. I don't know how to route the rest, or
if they should simply wait for 5.5 given how close we are to the merge
window for 5.4.

Rasmus Villemoes (6):
  staging: rtl8723bs: replace __inline by inline
  lib/zstd/mem.h: replace __inline by inline
  compiler_types.h: don't #define __inline
  compiler-types.h: add asm_inline definition
  x86: alternative.h: use asm_inline for all alternative variants
  x86: bug.h: use asm_inline in _BUG_FLAGS definitions

 arch/x86/include/asm/alternative.h              | 14 +++++++-------
 arch/x86/include/asm/bug.h                      |  4 ++--
 drivers/staging/rtl8723bs/core/rtw_pwrctrl.c    |  4 ++--
 drivers/staging/rtl8723bs/core/rtw_wlan_util.c  |  2 +-
 drivers/staging/rtl8723bs/include/drv_types.h   |  6 +++---
 .../staging/rtl8723bs/include/osdep_service.h   | 10 +++++-----
 .../rtl8723bs/include/osdep_service_linux.h     | 14 +++++++-------
 drivers/staging/rtl8723bs/include/rtw_mlme.h    | 14 +++++++-------
 drivers/staging/rtl8723bs/include/rtw_recv.h    | 16 ++++++++--------
 drivers/staging/rtl8723bs/include/sta_info.h    |  2 +-
 drivers/staging/rtl8723bs/include/wifi.h        | 14 +++++++-------
 drivers/staging/rtl8723bs/include/wlan_bssdef.h |  2 +-
 include/linux/compiler_types.h                  | 17 ++++++++++++++++-
 init/Kconfig                                    |  3 +++
 lib/zstd/mem.h                                  |  2 +-
 15 files changed, 71 insertions(+), 53 deletions(-)

-- 
2.20.1