linux-kernel - Re: [PATCH 7/7 v4] sh: mcount.S: fix build error when PRINTK is not enabled

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Message-ID: <c33548dd94ca23347a418743120aed4a552264a2.camel@physik.fu-berlin.de>
Date:   Mon, 20 Mar 2023 14:32:40 +0100
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, stable@...r.kernel.org,
        linux-sh <linux-sh@...r.kernel.org>
Subject: Re: [PATCH 7/7 v4] sh: mcount.S: fix build error when PRINTK is not
 enabled

Hi Geert!

On Mon, 2023-03-20 at 13:42 +0100, Geert Uytterhoeven wrote:
> Oops, obviously all of that happened before my morning coffee ;-)
> 
> Makefile has:
> 
>     ifdef CONFIG_FRAME_POINTER
>     KBUILD_CFLAGS   += -fno-omit-frame-pointer -fno-optimize-sibling-calls
>     KBUILD_RUSTFLAGS += -Cforce-frame-pointers=y
>     else
>     # Some targets (ARM with Thumb2, for example), can't be built with frame
>     # pointers.  For those, we don't have FUNCTION_TRACER automatically
>     # select FRAME_POINTER.  However, FUNCTION_TRACER adds -pg, and this is
>     # incompatible with -fomit-frame-pointer with current GCC, so we don't use
>     # -fomit-frame-pointer with FUNCTION_TRACER.
>     # In the Rust target specification, "frame-pointer" is set explicitly
>     # to "may-omit".
>     ifndef CONFIG_FUNCTION_TRACER
>     KBUILD_CFLAGS   += -fomit-frame-pointer
>     endif
>     endif
> 
> Your config probably has CONFIG_FRAME_POINTER set?
> 
>     arch/sh/Kconfig.debug=config DWARF_UNWINDER
>     arch/sh/Kconfig.debug-  bool "Enable the DWARF unwinder for stacktraces"
>     arch/sh/Kconfig.debug-  depends on DEBUG_KERNEL
>     arch/sh/Kconfig.debug:  select FRAME_POINTER
> 
> You should make sure that cannot happen when CONFIG_FUNCTION_TRACER
> is enabled. I.e. make DWARF_UNWINDER depend on !FUNCTION_TRACER?
> 
> Other architectures do something similar:
> 
>     arch/sparc/Kconfig.debug:config FRAME_POINTER
>     arch/sparc/Kconfig.debug-       bool
>     arch/sparc/Kconfig.debug-       depends on MCOUNT
> 
>     arch/x86/Kconfig.debug:config FRAME_POINTER
>     arch/x86/Kconfig.debug- depends on !UNWINDER_ORC && !UNWINDER_GUESS
>     arch/x86/Kconfig.debug- bool
> 
> Probably you need to adjust the following, too:
> 
>     lib/Kconfig.debug:config FRAME_POINTER
>     lib/Kconfig.debug-      bool "Compile the kernel with frame pointers"
>     lib/Kconfig.debug-      depends on DEBUG_KERNEL && (M68K || UML ||
> SUPERH) || ARCH_WANT_FRAME_POINTERS
>     lib/Kconfig.debug-      default y if (DEBUG_INFO && UML) ||
> ARCH_WANT_FRAME_POINTERS
> 
> i.e. drop SUPERH from the list above, and select ARCH_WANT_FRAME_POINTERS
> if !FUNCTION_TRACER.

Do you think you can send a patch for this change? I can then review and apply
it together with Randy's series in case everything works as expected.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
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