From:   Mark Rutland <mark.rutland@arm.com>
To:     linux-arm-kernel@lists.infradead.org
Cc:     catalin.marinas@arm.com, lenb@kernel.org,
        linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
        mark.rutland@arm.com, mhiramat@kernel.org, ndesaulniers@google.com,
        ojeda@kernel.org, peterz@infradead.org, rafael.j.wysocki@intel.com,
        revest@chromium.org, robert.moore@intel.com, rostedt@goodmis.org,
        will@kernel.org
Subject: [PATCH v3 3/8] ACPI: Don't build ACPICA with '-Os'
Date:   Mon, 23 Jan 2023 13:45:58 +0000
Message-Id: <20230123134603.1064407-4-mark.rutland@arm.com>
In-Reply-To: <20230123134603.1064407-1-mark.rutland@arm.com>
References: <20230123134603.1064407-1-mark.rutland@arm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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@arm.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Moore <robert.moore@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Cc: linux-acpi@vger.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