[v2] unwind, arm64: add sframe unwinder for kernel

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

Posted by Dylan Hatch 5 months ago

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>
---
 Makefile                          |  8 ++++++++
 arch/Kconfig                      |  6 ++++++
 arch/arm64/Kconfig.debug          | 10 ++++++++++
 arch/arm64/kernel/vdso/Makefile   |  2 +-
 include/asm-generic/vmlinux.lds.h | 15 +++++++++++++++
 5 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index b9c661913250..09972c71a3e8 100644
--- a/Makefile
+++ b/Makefile
@@ -1078,6 +1078,14 @@ endif
 # Ensure compilers do not transform certain loops into calls to wcslen()
 KBUILD_CFLAGS += -fno-builtin-wcslen
 
+# build with sframe table
+ifdef CONFIG_SFRAME_UNWIND_TABLE
+CC_FLAGS_SFRAME := -Wa,--gsframe
+KBUILD_CFLAGS	+= $(CC_FLAGS_SFRAME)
+KBUILD_AFLAGS	+= $(CC_FLAGS_SFRAME)
+export CC_FLAGS_SFRAME
+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 d1b4ffd6e085..4362d2f49d91 100644
--- 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)
+
+config SFRAME_UNWIND_TABLE
+	bool
+
 endmenu
diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index 265c4461031f..d64bf58457de 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_SFRAME
+	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 directly generated
+	  by toolchain based on DWARF CFI information.
+
 source "drivers/hwtracing/coresight/Kconfig"
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index 7dec05dd33b7..c60ef921956f 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -38,7 +38,7 @@ ccflags-y += -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
 CC_FLAGS_REMOVE_VDSO := $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) \
 			$(RANDSTRUCT_CFLAGS) $(KSTACK_ERASE_CFLAGS) \
 			$(GCC_PLUGINS_CFLAGS) \
-			$(CC_FLAGS_LTO) $(CC_FLAGS_CFI) \
+			$(CC_FLAGS_LTO) $(CC_FLAGS_CFI) $(CC_FLAGS_SFRAME) \
 			-Wmissing-prototypes -Wmissing-declarations
 
 CC_FLAGS_ADD_VDSO := -O2 -mcmodel=tiny -fasynchronous-unwind-tables
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index ae2d2359b79e..4f486080e4fb 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -473,6 +473,8 @@ 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) \
@@ -891,6 +893,19 @@ 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) {		\
+		__start_sframe_header = .;			\
+		KEEP(*(.sframe))				\
+		KEEP(*(.init.sframe))				\
+		__stop_sframe_header = .;			\
+	}
+#else
+#define SFRAME
+#endif
+
 #ifdef CONFIG_PRINTK_INDEX
 #define PRINTK_INDEX							\
 	.printk_index : AT(ADDR(.printk_index) - LOAD_OFFSET) {		\
-- 
2.51.0.355.g5224444f11-goog

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

Posted by Jens Remus 2 months, 2 weeks ago

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

IBM

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

Posted by Will Deacon 2 months, 3 weeks ago

On Thu, Sep 04, 2025 at 10:38:45PM +0000, 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>
> ---
>  Makefile                          |  8 ++++++++
>  arch/Kconfig                      |  6 ++++++
>  arch/arm64/Kconfig.debug          | 10 ++++++++++
>  arch/arm64/kernel/vdso/Makefile   |  2 +-
>  include/asm-generic/vmlinux.lds.h | 15 +++++++++++++++
>  5 files changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index b9c661913250..09972c71a3e8 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1078,6 +1078,14 @@ endif
>  # Ensure compilers do not transform certain loops into calls to wcslen()
>  KBUILD_CFLAGS += -fno-builtin-wcslen
>  
> +# build with sframe table
> +ifdef CONFIG_SFRAME_UNWIND_TABLE
> +CC_FLAGS_SFRAME := -Wa,--gsframe
> +KBUILD_CFLAGS	+= $(CC_FLAGS_SFRAME)
> +KBUILD_AFLAGS	+= $(CC_FLAGS_SFRAME)
> +export CC_FLAGS_SFRAME
> +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 d1b4ffd6e085..4362d2f49d91 100644
> --- 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)

Is it possible to extend this check so that we reject assemblers that
emit the unsupported "sframe version one" format?

> +config SFRAME_UNWIND_TABLE
> +	bool

Is this extra option actually needed for anything?

>  endmenu
> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
> index 265c4461031f..d64bf58457de 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_SFRAME
> +	depends on 64BIT

Shouldn't there be an arch dependency here as well? Since architectures
need to make use of sframe in their unwinders, I was expecting something
like 'depends on ARCH_SUPPORTS_SFRAME_UNWINDER' here.

Will

[PATCH v2 1/6] unwind: build kernel with sframe info
[PATCH v2 2/6] arm64: entry: add unwind info for various kernel entries
[PATCH v2 3/6] unwind: add sframe v2 header
[PATCH v2 4/6] unwind: Implement generic sframe unwinder library
[PATCH v2 5/6] arm64/module, unwind: Add sframe support for modules.
[PATCH v2 6/6] unwind: arm64: Add reliable stacktrace with sframe unwinder.