linux-kernel - Re: [PATCH 1/8] unwind: build kernel with sframe info

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Message-ID: <303e0c91-2351-4ccd-8948-b400ac5d2b7f@oracle.com>
Date: Tue, 4 Feb 2025 16:22:27 -0800
From: Indu Bhagat <indu.bhagat@...cle.com>
To: Weinan Liu <wnliu@...gle.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc: Mark Rutland <mark.rutland@....com>, roman.gushchin@...ux.dev,
        Will Deacon <will@...nel.org>, Ian Rogers <irogers@...gle.com>,
        linux-toolchains@...r.kernel.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org, joe.lawrence@...hat.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/8] unwind: build kernel with sframe info

On 1/27/25 1:33 PM, Weinan Liu wrote:
> Use the -Wa,--gsframe flags to build the code, so GAS will generate
> a new .sframe section for the stack trace information.
> Currently, the sframe format only supports arm64 and x86_64
> architectures. Add this configuration on arm64 to enable sframe
> unwinder in the future.
> 
> Signed-off-by: Weinan Liu <wnliu@...gle.com>
> ---
>   Makefile                          |  6 ++++++
>   arch/Kconfig                      |  8 ++++++++
>   arch/arm64/Kconfig.debug          | 10 ++++++++++
>   include/asm-generic/vmlinux.lds.h | 12 ++++++++++++
>   4 files changed, 36 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index b9464c88ac72..35200c39b98d 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1064,6 +1064,12 @@ ifdef CONFIG_CC_IS_GCC
>   KBUILD_CFLAGS   += -fconserve-stack
>   endif
>   
> +# build with sframe table
> +ifdef CONFIG_SFRAME_UNWIND_TABLE
> +KBUILD_CFLAGS	+= -Wa,--gsframe
> +KBUILD_AFLAGS	+= -Wa,--gsframe
> +endif
> +
>   # change __FILE__ to the relative path to the source directory
>   ifdef building_out_of_srctree
>   KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srcroot)/=)
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 6682b2a53e34..ae70f7dbe326 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1736,4 +1736,12 @@ config ARCH_WANTS_PRE_LINK_VMLINUX
>   	  An architecture can select this if it provides arch/<arch>/tools/Makefile
>   	  with .arch.vmlinux.o target to be linked into vmlinux.
>   
> +config AS_HAS_SFRAME_SUPPORT
> +	# Detect availability of the AS option -Wa,--gsframe for generating
> +	# sframe unwind table.
> +	def_bool $(cc-option,-Wa$(comma)--gsframe)
> +

Since the version of an admissible SFrame section needs to be atleast 
SFRAME_VERSION_2, it will make sense to include SFrame version check 
when detecting compatible toolchain.

> +config SFRAME_UNWIND_TABLE
> +	bool
> +
>   endmenu
> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
> index 265c4461031f..ed619fcb18b3 100644
> --- a/arch/arm64/Kconfig.debug
> +++ b/arch/arm64/Kconfig.debug
> @@ -20,4 +20,14 @@ config ARM64_RELOC_TEST
>   	depends on m
>   	tristate "Relocation testing module"
>   
> +config SFRAME_UNWINDER
> +	bool "Sframe unwinder"
> +	depends on AS_HAS_SFRAME_SUPPORT
> +	depends on 64BIT
> +	select SFRAME_UNWIND_TABLE
> +	help
> +	  This option enables the sframe (Simple Frame) unwinder for unwinding
> +	  kernel stack traces. It uses unwind table that is direclty generated
> +	  by toolchain based on DWARF CFI information
> +
>   source "drivers/hwtracing/coresight/Kconfig"
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 54504013c749..6a437bd084c7 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -469,6 +469,8 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
>   		*(.rodata1)						\
>   	}								\
>   									\
> +	SFRAME								\
> +									\
>   	/* PCI quirks */						\
>   	.pci_fixup        : AT(ADDR(.pci_fixup) - LOAD_OFFSET) {	\
>   		BOUNDED_SECTION_PRE_LABEL(.pci_fixup_early,  _pci_fixups_early,  __start, __end) \
> @@ -886,6 +888,16 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
>   #define TRACEDATA
>   #endif
>   
> +#ifdef CONFIG_SFRAME_UNWIND_TABLE
> +#define SFRAME							\
> +	/* sframe */						\
> +	.sframe        : AT(ADDR(.sframe) - LOAD_OFFSET) {	\
> +		BOUNDED_SECTION_BY(.sframe, _sframe_header)	\
> +	}
> +#else
> +#define SFRAME
> +#endif
> +
>   #ifdef CONFIG_PRINTK_INDEX
>   #define PRINTK_INDEX							\
>   	.printk_index : AT(ADDR(.printk_index) - LOAD_OFFSET) {		\