[PATCH v4 2/8] arm64, unwind: build kernel with sframe V3 info

[Dylan Hatch <dylanbhatch@google.com>]

Build with -Wa,--gsframe-3 flags to generate a .sframe section. 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.

Signed-off-by: Weinan Liu <wnliu@google.com>
Reviewed-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
Signed-off-by: Dylan Hatch <dylanbhatch@google.com>
---
 MAINTAINERS                            |  1 +
 Makefile                               |  8 ++++++++
 arch/Kconfig                           | 21 +++++++++++++++++++++
 arch/arm64/Kconfig                     |  1 +
 arch/arm64/include/asm/unwind_sframe.h |  8 ++++++++
 arch/arm64/kernel/vdso/Makefile        |  2 +-
 include/asm-generic/sections.h         |  4 ++++
 include/asm-generic/vmlinux.lds.h      | 15 +++++++++++++++
 8 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm64/include/asm/unwind_sframe.h

diff --git a/MAINTAINERS b/MAINTAINERS
index cfc7dec88da4..a7d75f9cb5f4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -27561,6 +27561,7 @@ 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/sframe.h
 F:	include/linux/unwind*.h
 F:	kernel/unwind/
diff --git a/Makefile b/Makefile
index 2b15f0b4a0cb..6c94a5257679 100644
--- a/Makefile
+++ b/Makefile
@@ -1110,6 +1110,14 @@ endif
 # Ensure compilers do not transform certain loops into calls to wcslen()
 KBUILD_CFLAGS += -fno-builtin-wcslen
 
+# 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 d7caf2e245ce..8d27b3249e7a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -520,6 +520,27 @@ config SFRAME_VALIDATION
 
 	  If unsure, say N.
 
+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 unwind an 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 38dba5f7e4d2..f7ae8eaaadc4 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -112,6 +112,7 @@ 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/include/asm/unwind_sframe.h b/arch/arm64/include/asm/unwind_sframe.h
new file mode 100644
index 000000000000..876412881196
--- /dev/null
+++ b/arch/arm64/include/asm/unwind_sframe.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ARM64_UNWIND_SFRAME_H
+#define _ASM_ARM64_UNWIND_SFRAME_H
+
+#define SFRAME_REG_SP	31
+#define SFRAME_REG_FP	29
+
+#endif /* _ASM_ARM64_UNWIND_SFRAME_H */
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/sections.h b/include/asm-generic/sections.h
index 0755bc39b0d8..336d27011a58 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 1e1580febe4b..090da633db92 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) \
@@ -911,6 +913,19 @@
 #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) {		\
-- 
2.54.0.rc1.555.g9c883467ad-goog