[RFC PATCH v1 04/16] s390/vdso: Enable SFrame generation in vDSO

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

This replicates Josh's commit TODO ("x86/vdso: Enable sframe generation
in VDSO") for s390.

Enable SFrame generation in the vDSO library so kernel and user space
can unwind through it.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Link to latest x86 patch:
    https://lore.kernel.org/all/20250425024023.173709192@goodmis.org/

 arch/s390/include/asm/dwarf.h        | 4 ++++
 arch/s390/kernel/vdso64/Makefile     | 7 ++++++-
 arch/s390/kernel/vdso64/vdso64.lds.S | 5 +++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/dwarf.h b/arch/s390/include/asm/dwarf.h
index 5052ee6a40f7..aeb54e716d5a 100644
--- a/arch/s390/include/asm/dwarf.h
+++ b/arch/s390/include/asm/dwarf.h
@@ -16,7 +16,11 @@
 	 * symbols for the .dbg file.
 	 */
 
+#ifdef CONFIG_AS_SFRAME
+	.cfi_sections .eh_frame, .debug_frame, .sframe
+#else
 	.cfi_sections .eh_frame, .debug_frame
+#endif
 
 #define CFI_STARTPROC		.cfi_startproc
 #define CFI_ENDPROC		.cfi_endproc
diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
index d8f0df742809..e96156b9c4df 100644
--- a/arch/s390/kernel/vdso64/Makefile
+++ b/arch/s390/kernel/vdso64/Makefile
@@ -20,7 +20,11 @@ targets := $(obj-vdso64) $(obj-cvdso64) vdso64.so vdso64.so.dbg
 obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
 obj-cvdso64 := $(addprefix $(obj)/, $(obj-cvdso64))
 
-KBUILD_AFLAGS += -DBUILD_VDSO
+ifeq ($(CONFIG_AS_SFRAME),y)
+	SFRAME_CFLAGS := -Wa,--gsframe
+endif
+
+KBUILD_AFLAGS += -DBUILD_VDSO $(SFRAME_CFLAGS)
 KBUILD_CFLAGS += -DBUILD_VDSO -DDISABLE_BRANCH_PROFILING
 
 KBUILD_AFLAGS_64 := $(filter-out -m64,$(KBUILD_AFLAGS))
@@ -32,6 +36,7 @@ KBUILD_CFLAGS_64 := $(filter-out -mno-pic-data-is-text-relative,$(KBUILD_CFLAGS_
 KBUILD_CFLAGS_64 := $(filter-out -munaligned-symbols,$(KBUILD_CFLAGS_64))
 KBUILD_CFLAGS_64 := $(filter-out -fno-asynchronous-unwind-tables,$(KBUILD_CFLAGS_64))
 KBUILD_CFLAGS_64 += -m64 -fPIC -fno-common -fno-builtin -fasynchronous-unwind-tables
+KBUILD_CFLAGS_64 += $(SFRAME_CFLAGS)
 ldflags-y := -shared -soname=linux-vdso64.so.1 \
 	     --hash-style=both --build-id=sha1 -T
 
diff --git a/arch/s390/kernel/vdso64/vdso64.lds.S b/arch/s390/kernel/vdso64/vdso64.lds.S
index e4f6551ae898..7acecb0d9b7e 100644
--- a/arch/s390/kernel/vdso64/vdso64.lds.S
+++ b/arch/s390/kernel/vdso64/vdso64.lds.S
@@ -50,6 +50,9 @@ SECTIONS
 
 	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr
 	.eh_frame	: { KEEP (*(.eh_frame)) }	:text
+
+	.sframe		: { *(.sframe) }		:text	:sframe
+
 	.gcc_except_table : { *(.gcc_except_table .gcc_except_table.*) }
 
 	.rela.dyn ALIGN(8) : { *(.rela.dyn) }
@@ -114,6 +117,7 @@ SECTIONS
  * Very old versions of ld do not recognize this name token; use the constant.
  */
 #define PT_GNU_EH_FRAME	0x6474e550
+#define PT_GNU_SFRAME	0x6474e554
 
 /*
  * We must supply the ELF program headers explicitly to get just one
@@ -125,6 +129,7 @@ PHDRS
 	dynamic		PT_DYNAMIC FLAGS(4);		/* PF_R */
 	note		PT_NOTE FLAGS(4);		/* PF_R */
 	eh_frame_hdr	PT_GNU_EH_FRAME;
+	sframe		PT_GNU_SFRAME;
 }
 
 /*
-- 
2.48.1