[PATCH v7 01/11] arm64, unwind: build kernel with sframe V3 info

[Dylan Hatch <dylanbhatch@google.com>]

To generate a .sframe section, build with -Wa,--gsframe-3 flags. Also,
add unwind-table options to ensure the necessary CFI directives are
emitted by the compiler, but discard .eh_frame unless
CONFIG_UNWIND_TABLES is explicitly enabled.

This will be used for in-kernel reliable stacktrace in
cases where the frame pointer alone is insufficient.

Currently, the sframe format only supports arm64, x86_64 and s390x
architectures.

Co-developed-by: Weinan Liu <wnliu@google.com>
Signed-off-by: Weinan Liu <wnliu@google.com>
Reviewed-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Dylan Hatch <dylanbhatch@google.com>

---

Changes since v6:
 - Moved to beginning of series
 - Squashed in AS_SFRAME, AS_SFRAME3, and UNWIND_SFRAME_LOOKUP config
   definitions.
 - Squashed in STACK UNWINDING change in MAINTAINERS file.
 - Dropped SFRAME_REG_SP / SFRAME_REG_FP definitions.
 - Added -fasynchronous-unwind-tables so CFI directives are emitted by
   compiler.
 - Discard .eh_frame sections when CONFIG_UNWIND_TABLES is not set.
---
 MAINTAINERS                         |  3 ++-
 Makefile                            |  8 ++++++++
 arch/Kconfig                        | 31 +++++++++++++++++++++++++++++
 arch/arm64/Kconfig                  |  1 +
 arch/arm64/Makefile                 |  2 +-
 arch/arm64/include/asm/module.lds.h |  2 ++
 arch/arm64/kernel/vdso/Makefile     |  2 +-
 arch/arm64/kernel/vmlinux.lds.S     | 12 +++++++++++
 include/asm-generic/sections.h      |  4 ++++
 include/asm-generic/vmlinux.lds.h   | 15 ++++++++++++++
 10 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index c2414447892c2..6c1c95979e437 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -28514,10 +28514,11 @@ F:	Documentation/driver-api/uio-howto.rst
 F:	drivers/uio/
 F:	include/linux/uio_driver.h
 
-USERSPACE STACK UNWINDING
+STACK UNWINDING
 M:	Josh Poimboeuf <jpoimboe@kernel.org>
 M:	Steven Rostedt <rostedt@goodmis.org>
 S:	Maintained
+F:	arch/*/include/asm/unwind_sframe.h
 F:	include/linux/unwind*.h
 F:	kernel/unwind/
 
diff --git a/Makefile b/Makefile
index 0f1b80100b479..5ed4a59e71aac 100644
--- a/Makefile
+++ b/Makefile
@@ -1197,6 +1197,14 @@ CFLAGS_GCOV	+= $(call try-run,\
 endif
 export CFLAGS_GCOV
 
+# build with sframe table
+ifdef CONFIG_HAVE_UNWIND_KERNEL_SFRAME
+CC_FLAGS_SFRAME := -Wa,--gsframe-3
+KBUILD_CFLAGS	+= $(CC_FLAGS_SFRAME)
+KBUILD_AFLAGS	+= $(CC_FLAGS_SFRAME)
+export CC_FLAGS_SFRAME
+endif
+
 # change __FILE__ to the relative path to the source directory
 ifdef building_out_of_srctree
 KBUILD_CPPFLAGS += -fmacro-prefix-map=$(srcroot)/=
diff --git a/arch/Kconfig b/arch/Kconfig
index 45c6577723623..cc59a5da80915 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -507,6 +507,37 @@ config HAVE_UNWIND_USER_FP
 	bool
 	select UNWIND_USER
 
+config AS_SFRAME
+	bool
+
+config AS_SFRAME3
+	def_bool $(as-instr,.cfi_startproc\n.cfi_endproc,-Wa$(comma)--gsframe-3)
+	select AS_SFRAME
+
+config UNWIND_SFRAME_LOOKUP
+	bool
+
+config ARCH_SUPPORTS_UNWIND_KERNEL_SFRAME
+	bool
+	help
+	  An architecture can select this if it enables the SFrame (Simple
+	  Frame) unwinder for unwinding kernel stack traces. It uses an unwind
+	  table that is directly generated by the toolchain based on DWARF CFI
+	  information.
+
+config HAVE_UNWIND_KERNEL_SFRAME
+	bool "Sframe unwinder"
+	depends on AS_SFRAME3
+	depends on 64BIT
+	depends on ARCH_SUPPORTS_UNWIND_KERNEL_SFRAME
+	select UNWIND_SFRAME_LOOKUP
+	help
+	  This option enables the SFrame (Simple Frame) unwinder for unwinding
+	  kernel stack traces. It uses an unwind table that is directly
+	  generated by the toolchain based on DWARF CFI information. In
+	  practice, this can provide more reliable stacktrace results than
+	  unwinding with frame pointers alone.
+
 config HAVE_PERF_REGS
 	bool
 	help
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b5a51b0ef9440..041de63a659d1 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -87,6 +87,7 @@ config ARM64
 	select ARCH_SUPPORTS_SCHED_SMT
 	select ARCH_SUPPORTS_SCHED_CLUSTER
 	select ARCH_SUPPORTS_SCHED_MC
+	select ARCH_SUPPORTS_UNWIND_KERNEL_SFRAME
 	select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
 	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT
 	select ARCH_WANT_DEFAULT_BPF_JIT
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 6b005c8fef706..ae1c23579ad2f 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -55,7 +55,7 @@ KBUILD_CFLAGS	+= $(call cc-option,-mabi=lp64)
 KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
 
 # Avoid generating .eh_frame* sections.
-ifneq ($(CONFIG_UNWIND_TABLES),y)
+ifeq ($(filter y, $(CONFIG_UNWIND_TABLES) $(CONFIG_HAVE_UNWIND_KERNEL_SFRAME)),)
 KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables -fno-unwind-tables
 KBUILD_AFLAGS	+= -fno-asynchronous-unwind-tables -fno-unwind-tables
 KBUILD_RUSTFLAGS += -Cforce-unwind-tables=n
diff --git a/arch/arm64/include/asm/module.lds.h b/arch/arm64/include/asm/module.lds.h
index 603f92a8a73ed..034cb635e8bcc 100644
--- a/arch/arm64/include/asm/module.lds.h
+++ b/arch/arm64/include/asm/module.lds.h
@@ -10,5 +10,7 @@ SECTIONS {
 	 * put it into the .init allocation.
 	 */
 	.init.eh_frame 0 : { *(.eh_frame) }
+#elif defined(CONFIG_HAVE_UNWIND_KERNEL_SFRAME)
+	/DISCARD/ : { *(.eh_frame) }
 #endif
 }
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index 7dec05dd33b70..c60ef921956fb 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/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index af1d720209764..eb1f54829503c 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -145,14 +145,25 @@ jiffies = jiffies_64;
 #endif
 
 #ifdef CONFIG_UNWIND_TABLES
+
 #define UNWIND_DATA_SECTIONS				\
 	.eh_frame : {					\
 		__pi___eh_frame_start = .;		\
 		*(.eh_frame)				\
 		__pi___eh_frame_end = .;		\
 	}
+#define SFRAME_DISCARDS
+
+#elif defined(CONFIG_HAVE_UNWIND_KERNEL_SFRAME)
+
+#define UNWIND_DATA_SECTIONS
+#define SFRAME_DISCARDS *(.eh_frame)
+
 #else
+
 #define UNWIND_DATA_SECTIONS
+#define SFRAME_DISCARDS
+
 #endif
 
 /*
@@ -184,6 +195,7 @@ SECTIONS
 		*(.interp .dynamic)
 		*(.dynsym .dynstr .hash .gnu.hash)
 		*(.ARM.attributes)
+		SFRAME_DISCARDS
 	}
 
 	. = KIMAGE_VADDR;
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index 0755bc39b0d80..336d27011a580 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -31,6 +31,7 @@
  *	__irqentry_text_start, __irqentry_text_end
  *	__softirqentry_text_start, __softirqentry_text_end
  *	__start_opd, __end_opd
+ *	__start_sframe, __end_sframe
  */
 extern char _text[], _stext[], _etext[];
 extern char _data[], _sdata[], _edata[];
@@ -53,6 +54,9 @@ extern char __ctors_start[], __ctors_end[];
 /* Start and end of .opd section - used for function descriptors. */
 extern char __start_opd[], __end_opd[];
 
+/* Start and end of .sframe section - used for stack unwinding. */
+extern char __start_sframe[], __end_sframe[];
+
 /* Start and end of instrumentation protected text section */
 extern char __noinstr_text_start[], __noinstr_text_end[];
 
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2988aa12f664..278f5764d990d 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -491,6 +491,8 @@
 		*(.rodata1)						\
 	}								\
 									\
+	SFRAME								\
+									\
 	/* PCI quirks */						\
 	.pci_fixup        : AT(ADDR(.pci_fixup) - LOAD_OFFSET) {	\
 		BOUNDED_SECTION_PRE_LABEL(.pci_fixup_early,  _pci_fixups_early,  __start, __end) \
@@ -912,6 +914,19 @@
 #define TRACEDATA
 #endif
 
+#ifdef CONFIG_HAVE_UNWIND_KERNEL_SFRAME
+#define SFRAME							\
+	/* sframe */						\
+	.sframe : AT(ADDR(.sframe) - LOAD_OFFSET) {		\
+		__start_sframe = .;			\
+		KEEP(*(.sframe))				\
+		KEEP(*(.init.sframe))				\
+		__end_sframe = .;			\
+	}
+#else
+#define SFRAME
+#endif
+
 #ifdef CONFIG_PRINTK_INDEX
 #define PRINTK_INDEX							\
 	.printk_index : AT(ADDR(.printk_index) - LOAD_OFFSET) {		\
-- 
2.55.0.1082.g2b9226bbc0-goog