Re: [PATCH v2 1/6] unwind: build kernel with sframe info

[Jens Remus <jremus@linux.ibm.com>]

Hello Dylan!

On 9/5/2025 12:38 AM, Dylan Hatch 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@google.com>
> Signed-off-by: Dylan Hatch <dylanbhatch@google.com>
> Reviewed-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>

> diff --git a/arch/Kconfig b/arch/Kconfig

> @@ -1782,4 +1782,10 @@ config ARCH_WANTS_PRE_LINK_VMLINUX
>  config ARCH_HAS_CPU_ATTACK_VECTORS
>  	bool
>  
> +config AS_SFRAME
> +	def_bool $(as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc)

As you will soon be requiring SFrame V2 with the new PC-relative FDE
function start address encoding you may want to extend this check as
follows:

config AS_SFRAME
	def_bool y
	depends on $(as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc)
	depends on $(success,printf "%b\n" ".cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc" | $(CC) $(CLANG_FLAGS) -Wa$(comma)--fatal-warnings -c -x assembler-with-cpp -o "$$TMP" - && $(OBJDUMP) --sframe "$$TMP" | grep -q "SFRAME_VERSION_2")
	depends on $(success,printf "%b\n" ".cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc" | $(CC) $(CLANG_FLAGS) -Wa$(comma)--fatal-warnings -c -x assembler-with-cpp -o "$$TMP" - && $(OBJDUMP) --sframe "$$TMP" | grep -q "SFRAME_F_FDE_FUNC_START_PCREL")


Or you could change it into multiple config options, which might be
overkill:

config AS_SFRAME
	def_bool $(as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc)

config AS_SFRAME_V2
	def_bool y
	depends on AS_SFRAME
	depends on $(success,printf "%b\n" ".cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc" | $(CC) $(CLANG_FLAGS) -Wa$(comma)--fatal-warnings -c -x assembler-with-cpp -o "$$TMP" - && $(OBJDUMP) --sframe "$$TMP" | grep -q "SFRAME_VERSION_2")

config AS_SFRAME_V2_PCREL_FDE
	def_bool y
	depends on AS_SFRAME_V2
	depends on $(success,printf "%b\n" ".cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc" | $(CC) $(CLANG_FLAGS) -Wa$(comma)--fatal-warnings -c -x assembler-with-cpp -o "$$TMP" - && $(OBJDUMP) --sframe "$$TMP" | grep -q "SFRAME_F_FDE_FUNC_START_PCREL")

> +
> +config SFRAME_UNWIND_TABLE
> +	bool
> +
>  endmenu
Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com

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