linux-kernel - [tip: locking/urgent] jump_labels: Mark __jump_label_transform() as __always_inlined to work around aggressive compiler un-inlining

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Date:   Tue, 13 Jul 2021 04:36:17 -0000
From:   "tip-bot2 for Ingo Molnar" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/urgent] jump_labels: Mark __jump_label_transform() as
 __always_inlined to work around aggressive compiler un-inlining

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID:     e48a12e546ecbfb0718176037eae0ad60598a29a
Gitweb:        https://git.kernel.org/tip/e48a12e546ecbfb0718176037eae0ad60598a29a
Author:        Ingo Molnar <mingo@...nel.org>
AuthorDate:    Tue, 13 Jul 2021 06:16:05 +02:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 13 Jul 2021 06:32:05 +02:00

jump_labels: Mark __jump_label_transform() as __always_inlined to work around aggressive compiler un-inlining

In randconfig testing, certain UBSAN and CC Kconfig combinations
with GCC 10.3.0:

  CONFIG_X86_32=y

  CONFIG_CC_OPTIMIZE_FOR_SIZE=y

  CONFIG_UBSAN=y
  # CONFIG_UBSAN_TRAP is not set
  # CONFIG_UBSAN_BOUNDS is not set
  CONFIG_UBSAN_SHIFT=y
  # CONFIG_UBSAN_DIV_ZERO is not set
  CONFIG_UBSAN_UNREACHABLE=y
  CONFIG_UBSAN_BOOL=y
  # CONFIG_UBSAN_ENUM is not set
  # CONFIG_UBSAN_ALIGNMENT is not set
  # CONFIG_UBSAN_SANITIZE_ALL is not set

... produce this build warning (and build error if
CONFIG_SECTION_MISMATCH_WARN_ONLY=y is set):

  WARNING: modpost: vmlinux.o(.text+0x4c1cc): Section mismatch in reference from the function __jump_label_transform() to the function .init.text:text_poke_early()
  The function __jump_label_transform() references
  the function __init text_poke_early().
  This is often because __jump_label_transform lacks a __init
  annotation or the annotation of text_poke_early is wrong.

  ERROR: modpost: Section mismatches detected.

The problem is that __jump_label_transform() gets uninlined by GCC,
despite there being only a single local scope user of the 'static inline'
function.

Mark the function __always_inline instead, to work around this compiler
bug/artifact.

Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/jump_label.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index 674906f..68f091b 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -79,9 +79,10 @@ __jump_label_patch(struct jump_entry *entry, enum jump_label_type type)
 	return (struct jump_label_patch){.code = code, .size = size};
 }

-static inline void __jump_label_transform(struct jump_entry *entry,
-					  enum jump_label_type type,
-					  int init)
+static __always_inline void
+__jump_label_transform(struct jump_entry *entry,
+		       enum jump_label_type type,
+		       int init)
 {
 	const struct jump_label_patch jlp = __jump_label_patch(entry, type);