linux-kernel - [PATCH v2 2/8] ACPI: Don't build ACPICA with '-Os'

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Message-Id: <20230113180355.2930042-3-mark.rutland@arm.com>
Date:   Fri, 13 Jan 2023 18:03:49 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     catalin.marinas@....com, lenb@...nel.org,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, mhiramat@...nel.org, ndesaulniers@...gle.com,
        ojeda@...nel.org, peterz@...radead.org, rafael.j.wysocki@...el.com,
        revest@...omium.org, robert.moore@...el.com, rostedt@...dmis.org,
        will@...nel.org
Subject: [PATCH v2 2/8] ACPI: Don't build ACPICA with '-Os'

The ACPICA code has been built with '-Os' since the beginning of git
history, though there's no explanatory comment as to why.

This is unfortunate as GCC drops the alignment specificed by
'-falign-functions=N' when '-Os' is used, as reported in GCC bug 88345:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345

This prevents CONFIG_FUNCTION_ALIGNMENT and
CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B from having their expected effect
on the ACPICA code. This is doubly unfortunate as in subsequent patches
arm64 will depend upon CONFIG_FUNCTION_ALIGNMENT for its ftrace
implementation.

Drop the '-Os' flag when building the ACPICA code. With this removed,
the code builds cleanly and works correctly in testing so far.

I've tested this by selecting CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B=y,
building and booting a kernel using ACPI, and looking for misaligned
text symbols:

* arm64:

  Before, v6.2-rc3:
    # uname -rm
    6.2.0-rc3 aarch64
    # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | wc -l
    5009

  Before, v6.2-rc3 + fixed __cold:
    # uname -rm
    6.2.0-rc3-00001-g2a2bedf8bfa9 aarch64
    # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | wc -l
    919

  After:
    # uname -rm
    6.2.0-rc3-00002-g267bddc38572 aarch64
    # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | wc -l
    323
    # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | grep acpi | wc -l
    0

* x86_64:

  Before, v6.2-rc3:
    # uname -rm
    6.2.0-rc3 x86_64
    # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | wc -l
    11537

  Before, v6.2-rc3 + fixed __cold:
    # uname -rm
    6.2.0-rc3-00001-g2a2bedf8bfa9 x86_64
    # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | wc -l
    2805

  After:
    # uname -rm
    6.2.0-rc3-00002-g267bddc38572 x86_64
    # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | wc -l
    1357
    # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | grep acpi | wc -l
    0

With the patch applied, the remaining unaligned text labels are a
combination of static call trampolines and labels in assembly, which can
be dealt with in subsequent patches.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Florent Revest <revest@...omium.org>
Cc: Len Brown <lenb@...nel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Robert Moore <robert.moore@...el.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Will Deacon <will@...nel.org>
Cc: linux-acpi@...r.kernel.org
---
 drivers/acpi/acpica/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/acpica/Makefile b/drivers/acpi/acpica/Makefile
index 9e0d95d76fff..30f3fc13c29d 100644
--- a/drivers/acpi/acpica/Makefile
+++ b/drivers/acpi/acpica/Makefile
@@ -3,7 +3,7 @@
 # Makefile for ACPICA Core interpreter
 #
 
-ccflags-y			:= -Os -D_LINUX -DBUILDING_ACPICA
+ccflags-y			:= -D_LINUX -DBUILDING_ACPICA
 ccflags-$(CONFIG_ACPI_DEBUG)	+= -DACPI_DEBUG_OUTPUT
 
 # use acpi.o to put all files here into acpi.o modparam namespace
-- 
2.30.2