[PATCH v5 0/6] x86/vdso: VDSO updates and fixes for sframes

[PATCH v5 0/6] x86/vdso: VDSO updates and fixes for sframes

[Steven Rostedt]

I'm currently working on getting sframe support from the kernel.
In order to do that, it requires some fixes. Josh Poimboeuf did
a lot of the hard work already, but he told me he doesn't have
time to continue it so I'm picking it up where he left off.

His last series of v4 is here:

  https://lore.kernel.org/all/cover.1737511963.git.jpoimboe@kernel.org/

It covers a lot of topics as he found issues with other aspects of
the kernel that needed to be fixed for sframes to work properly.

This series focuses only on the VDSO code. They are helpful fixes
and updates that doesn't rely on sframes (although the last patch
is sframe related).

I based this off of the latest tip/master:

 commit 7ab869c799fc0fb22f9b4c2f36aaa603d9c7cc9d

Patch 3 (Fix VDSO DWARF generation with kernel IBT enabled) had
a bit of conflicts with a clean up patch that removed ENDBR and
should be reviewed the most to make sure I didn't break anything.

The last patch I included the suggestions made by Jens Remus.

Other than that, the patches are basically the same. Hopefully they
can get into v6.16.

Head SHA1: 2d48d5dcf5308a87d3bb34027867ee347bf4fb6b


Josh Poimboeuf (6):
      x86/vdso: Fix DWARF generation for getrandom()
      x86/asm: Avoid emitting DWARF CFI for non-VDSO
      x86/asm: Fix VDSO DWARF generation with kernel IBT enabled
      x86/vdso: Use SYM_FUNC_{START,END} in __kernel_vsyscall()
      x86/vdso: Use CFI macros in __vdso_sgx_enter_enclave()
      x86/vdso: Enable sframe generation in VDSO

----
 arch/Kconfig                             |  3 ++
 arch/x86/entry/vdso/Makefile             | 10 ++++--
 arch/x86/entry/vdso/vdso-layout.lds.S    |  5 ++-
 arch/x86/entry/vdso/vdso32/system_call.S | 10 ++----
 arch/x86/entry/vdso/vgetrandom-chacha.S  |  3 +-
 arch/x86/entry/vdso/vsgx.S               | 19 +++++------
 arch/x86/include/asm/dwarf2.h            | 54 ++++++++++++++++++++++----------
 arch/x86/include/asm/linkage.h           | 33 +++++++++++++++----
 arch/x86/include/asm/vdso.h              |  1 -
 9 files changed, 89 insertions(+), 49 deletions(-)

[PATCH v5 1/6] x86/vdso: Fix DWARF generation for getrandom()

[Steven Rostedt]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Add CFI annotations to the VDSO implementation of getrandom() so it will
have valid DWARF unwinding metadata.

Fixes: 33385150ac45 ("x86: vdso: Wire up getrandom() vDSO implementation")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 arch/x86/entry/vdso/vgetrandom-chacha.S | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/vdso/vgetrandom-chacha.S b/arch/x86/entry/vdso/vgetrandom-chacha.S
index bcba5639b8ee..cc82da9216fb 100644
--- a/arch/x86/entry/vdso/vgetrandom-chacha.S
+++ b/arch/x86/entry/vdso/vgetrandom-chacha.S
@@ -4,7 +4,7 @@
  */
 
 #include <linux/linkage.h>
-#include <asm/frame.h>
+#include <asm/dwarf2.h>
 
 .section	.rodata, "a"
 .align 16
@@ -22,7 +22,7 @@ CONSTANTS:	.octa 0x6b20657479622d323320646e61707865
  *	rcx: number of 64-byte blocks to write to output
  */
 SYM_FUNC_START(__arch_chacha20_blocks_nostack)
-
+	CFI_STARTPROC
 .set	output,		%rdi
 .set	key,		%rsi
 .set	counter,	%rdx
@@ -175,4 +175,5 @@ SYM_FUNC_START(__arch_chacha20_blocks_nostack)
 	pxor		temp,temp
 
 	ret
+	CFI_ENDPROC
 SYM_FUNC_END(__arch_chacha20_blocks_nostack)
-- 
2.47.2

[PATCH v5 2/6] x86/asm: Avoid emitting DWARF CFI for non-VDSO

[Steven Rostedt]

From: Josh Poimboeuf <jpoimboe@kernel.org>

It was decided years ago that .cfi_* annotations aren't maintainable in
the kernel.  They were replaced by objtool unwind hints.  For the kernel
proper, ensure the CFI_* macros don't do anything.

On the other hand the VDSO library *does* use them, so user space can
unwind through it.

Make sure these macros only work for VDSO.  They aren't actually being
used outside of VDSO anyway, so there's no functional change.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 arch/x86/include/asm/dwarf2.h | 51 ++++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/dwarf2.h b/arch/x86/include/asm/dwarf2.h
index 302e11b15da8..65d958ef1178 100644
--- a/arch/x86/include/asm/dwarf2.h
+++ b/arch/x86/include/asm/dwarf2.h
@@ -6,6 +6,15 @@
 #warning "asm/dwarf2.h should be only included in pure assembly files"
 #endif
 
+#ifdef BUILD_VDSO
+
+	/*
+	 * For the vDSO, emit both runtime unwind information and debug
+	 * symbols for the .dbg file.
+	 */
+
+	.cfi_sections .eh_frame, .debug_frame
+
 #define CFI_STARTPROC		.cfi_startproc
 #define CFI_ENDPROC		.cfi_endproc
 #define CFI_DEF_CFA		.cfi_def_cfa
@@ -21,21 +30,31 @@
 #define CFI_UNDEFINED		.cfi_undefined
 #define CFI_ESCAPE		.cfi_escape
 
-#ifndef BUILD_VDSO
-	/*
-	 * Emit CFI data in .debug_frame sections, not .eh_frame sections.
-	 * The latter we currently just discard since we don't do DWARF
-	 * unwinding at runtime.  So only the offline DWARF information is
-	 * useful to anyone.  Note we should not use this directive if we
-	 * ever decide to enable DWARF unwinding at runtime.
-	 */
-	.cfi_sections .debug_frame
-#else
-	 /*
-	  * For the vDSO, emit both runtime unwind information and debug
-	  * symbols for the .dbg file.
-	  */
-	.cfi_sections .eh_frame, .debug_frame
-#endif
+#else /* !BUILD_VDSO */
+
+/*
+ * On x86, these macros aren't used outside VDSO.  As well they shouldn't be:
+ * they're fragile and very difficult to maintain.
+ */
+
+.macro nocfi args:vararg
+.endm
+
+#define CFI_STARTPROC		nocfi
+#define CFI_ENDPROC		nocfi
+#define CFI_DEF_CFA		nocfi
+#define CFI_DEF_CFA_REGISTER	nocfi
+#define CFI_DEF_CFA_OFFSET	nocfi
+#define CFI_ADJUST_CFA_OFFSET	nocfi
+#define CFI_OFFSET		nocfi
+#define CFI_REL_OFFSET		nocfi
+#define CFI_REGISTER		nocfi
+#define CFI_RESTORE		nocfi
+#define CFI_REMEMBER_STATE	nocfi
+#define CFI_RESTORE_STATE	nocfi
+#define CFI_UNDEFINED		nocfi
+#define CFI_ESCAPE		nocfi
+
+#endif /* !BUILD_VDSO */
 
 #endif /* _ASM_X86_DWARF2_H */
-- 
2.47.2

[PATCH v5 3/6] x86/asm: Fix VDSO DWARF generation with kernel IBT enabled

[Steven Rostedt]

From: Josh Poimboeuf <jpoimboe@kernel.org>

The DWARF .cfi_startproc annotation needs to be at the very beginning of
a function.  But with kernel IBT that doesn't happen as ENDBR is
sneakily embedded in SYM_FUNC_START.  As a result the DWARF unwinding
info is wrong at the beginning of all the VDSO functions.

Fix it by adding CFI_STARTPROC and CFI_ENDPROC to SYM_FUNC_START_* and
SYM_FUNC_END respectively.  Note this only affects VDSO, as the CFI_*
macros are empty for the kernel proper.

Fixes: c4691712b546 ("x86/linkage: Add ENDBR to SYM_FUNC_START*()")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
[ Fixed rebased issues. May need extra review ]
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v4: https://lore.kernel.org/all/5c7992c111adee94e242fbca2b3e64ab8e96e595.1737511963.git.jpoimboe@kernel.org/

- Rebased to latest kernel which had changes to the ENDBR caused by:
  582077c94052 ("x86/cfi: Clean up linkage")

 arch/x86/entry/vdso/vdso-layout.lds.S   |  2 +-
 arch/x86/entry/vdso/vgetrandom-chacha.S |  2 --
 arch/x86/entry/vdso/vsgx.S              |  4 ---
 arch/x86/include/asm/linkage.h          | 33 ++++++++++++++++++++-----
 arch/x86/include/asm/vdso.h             |  1 -
 5 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index ec1ac191a057..60747905de2b 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -1,5 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
-#include <asm/vdso.h>
+#include <asm/page_types.h>
 #include <asm/vdso/vsyscall.h>
 #include <vdso/datapage.h>
 
diff --git a/arch/x86/entry/vdso/vgetrandom-chacha.S b/arch/x86/entry/vdso/vgetrandom-chacha.S
index cc82da9216fb..a33212594731 100644
--- a/arch/x86/entry/vdso/vgetrandom-chacha.S
+++ b/arch/x86/entry/vdso/vgetrandom-chacha.S
@@ -22,7 +22,6 @@ CONSTANTS:	.octa 0x6b20657479622d323320646e61707865
  *	rcx: number of 64-byte blocks to write to output
  */
 SYM_FUNC_START(__arch_chacha20_blocks_nostack)
-	CFI_STARTPROC
 .set	output,		%rdi
 .set	key,		%rsi
 .set	counter,	%rdx
@@ -175,5 +174,4 @@ SYM_FUNC_START(__arch_chacha20_blocks_nostack)
 	pxor		temp,temp
 
 	ret
-	CFI_ENDPROC
 SYM_FUNC_END(__arch_chacha20_blocks_nostack)
diff --git a/arch/x86/entry/vdso/vsgx.S b/arch/x86/entry/vdso/vsgx.S
index 37a3d4c02366..c0342238c976 100644
--- a/arch/x86/entry/vdso/vsgx.S
+++ b/arch/x86/entry/vdso/vsgx.S
@@ -24,8 +24,6 @@
 .section .text, "ax"
 
 SYM_FUNC_START(__vdso_sgx_enter_enclave)
-	/* Prolog */
-	.cfi_startproc
 	push	%rbp
 	.cfi_adjust_cfa_offset	8
 	.cfi_rel_offset		%rbp, 0
@@ -143,8 +141,6 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
 	jle	.Lout
 	jmp	.Lenter_enclave
 
-	.cfi_endproc
-
 _ASM_VDSO_EXTABLE_HANDLE(.Lenclu_eenter_eresume, .Lhandle_exception)
 
 SYM_FUNC_END(__vdso_sgx_enter_enclave)
diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index b51d8a4673f5..1ba1f208414f 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -40,6 +40,10 @@
 
 #ifdef __ASSEMBLER__
 
+#ifndef LINKER_SCRIPT
+#include <asm/dwarf2.h>
+#endif
+
 #if defined(CONFIG_MITIGATION_RETHUNK) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
 #define RET	jmp __x86_return_thunk
 #else /* CONFIG_MITIGATION_RETPOLINE */
@@ -112,34 +116,51 @@
 # define SYM_FUNC_ALIAS_MEMFUNC	SYM_FUNC_ALIAS
 #endif
 
+#define __SYM_FUNC_START				\
+	CFI_STARTPROC ASM_NL
+
+#define __SYM_FUNC_END					\
+	CFI_ENDPROC ASM_NL
+
 /* SYM_TYPED_FUNC_START -- use for indirectly called globals, w/ CFI type */
 #define SYM_TYPED_FUNC_START(name)				\
 	SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_F_ALIGN)	\
+	__SYM_FUNC_START					\
 	ENDBR
 
 /* SYM_FUNC_START -- use for global functions */
 #define SYM_FUNC_START(name)				\
-	SYM_START(name, SYM_L_GLOBAL, SYM_F_ALIGN)
+	SYM_START(name, SYM_L_GLOBAL, SYM_F_ALIGN)	\
+	__SYM_FUNC_START
 
 /* SYM_FUNC_START_NOALIGN -- use for global functions, w/o alignment */
 #define SYM_FUNC_START_NOALIGN(name)			\
-	SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE)
+	SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE)	\
+	__SYM_FUNC_START
 
 /* SYM_FUNC_START_LOCAL -- use for local functions */
 #define SYM_FUNC_START_LOCAL(name)			\
-	SYM_START(name, SYM_L_LOCAL, SYM_F_ALIGN)
+	SYM_START(name, SYM_L_LOCAL, SYM_F_ALIGN)	\
+	__SYM_FUNC_START
 
 /* SYM_FUNC_START_LOCAL_NOALIGN -- use for local functions, w/o alignment */
 #define SYM_FUNC_START_LOCAL_NOALIGN(name)		\
-	SYM_START(name, SYM_L_LOCAL, SYM_A_NONE)
+	SYM_START(name, SYM_L_LOCAL, SYM_A_NONE)	\
+	__SYM_FUNC_START
 
 /* SYM_FUNC_START_WEAK -- use for weak functions */
 #define SYM_FUNC_START_WEAK(name)			\
-	SYM_START(name, SYM_L_WEAK, SYM_F_ALIGN)
+	SYM_START(name, SYM_L_WEAK, SYM_F_ALIGN)	\
+	__SYM_FUNC_START
 
 /* SYM_FUNC_START_WEAK_NOALIGN -- use for weak functions, w/o alignment */
 #define SYM_FUNC_START_WEAK_NOALIGN(name)		\
-	SYM_START(name, SYM_L_WEAK, SYM_A_NONE)
+	SYM_START(name, SYM_L_WEAK, SYM_A_NONE)		\
+	__SYM_FUNC_START
+
+#define SYM_FUNC_END(name)				\
+	__SYM_FUNC_END					\
+	SYM_END(name, SYM_T_FUNC)
 
 #endif /* _ASM_X86_LINKAGE_H */
 
diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h
index b7253ef3205a..c4290dadba66 100644
--- a/arch/x86/include/asm/vdso.h
+++ b/arch/x86/include/asm/vdso.h
@@ -2,7 +2,6 @@
 #ifndef _ASM_X86_VDSO_H
 #define _ASM_X86_VDSO_H
 
-#include <asm/page_types.h>
 #include <linux/linkage.h>
 #include <linux/init.h>
 
-- 
2.47.2

[PATCH v5 4/6] x86/vdso: Use SYM_FUNC_{START,END} in __kernel_vsyscall()

[Steven Rostedt]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Use SYM_FUNC_{START,END} instead of all the boilerplate.  No functional
change.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 arch/x86/entry/vdso/vdso32/system_call.S | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/x86/entry/vdso/vdso32/system_call.S b/arch/x86/entry/vdso/vdso32/system_call.S
index d33c6513fd2c..bdc576548240 100644
--- a/arch/x86/entry/vdso/vdso32/system_call.S
+++ b/arch/x86/entry/vdso/vdso32/system_call.S
@@ -9,11 +9,7 @@
 #include <asm/alternative.h>
 
 	.text
-	.globl __kernel_vsyscall
-	.type __kernel_vsyscall,@function
-	ALIGN
-__kernel_vsyscall:
-	CFI_STARTPROC
+SYM_FUNC_START(__kernel_vsyscall)
 	/*
 	 * Reshuffle regs so that all of any of the entry instructions
 	 * will preserve enough state.
@@ -79,7 +75,5 @@ SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL)
 	CFI_RESTORE		ecx
 	CFI_ADJUST_CFA_OFFSET	-4
 	RET
-	CFI_ENDPROC
-
-	.size __kernel_vsyscall,.-__kernel_vsyscall
+SYM_FUNC_END(__kernel_vsyscall)
 	.previous
-- 
2.47.2

[PATCH v5 5/6] x86/vdso: Use CFI macros in __vdso_sgx_enter_enclave()

[Steven Rostedt]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Use the CFI macros instead of the raw .cfi_* directives to be consistent
with the rest of the VDSO asm.  It's also easier on the eyes.

No functional changes.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 arch/x86/entry/vdso/vsgx.S | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/entry/vdso/vsgx.S b/arch/x86/entry/vdso/vsgx.S
index c0342238c976..8d7b8eb45c50 100644
--- a/arch/x86/entry/vdso/vsgx.S
+++ b/arch/x86/entry/vdso/vsgx.S
@@ -24,13 +24,14 @@
 .section .text, "ax"
 
 SYM_FUNC_START(__vdso_sgx_enter_enclave)
+	SYM_F_ALIGN
 	push	%rbp
-	.cfi_adjust_cfa_offset	8
-	.cfi_rel_offset		%rbp, 0
+	CFI_ADJUST_CFA_OFFSET	8
+	CFI_REL_OFFSET		%rbp, 0
 	mov	%rsp, %rbp
-	.cfi_def_cfa_register	%rbp
+	CFI_DEF_CFA_REGISTER	%rbp
 	push	%rbx
-	.cfi_rel_offset		%rbx, -8
+	CFI_REL_OFFSET		%rbx, -8
 
 	mov	%ecx, %eax
 .Lenter_enclave:
@@ -77,13 +78,11 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
 .Lout:
 	pop	%rbx
 	leave
-	.cfi_def_cfa		%rsp, 8
+	CFI_DEF_CFA		%rsp, 8
 	RET
 
-	/* The out-of-line code runs with the pre-leave stack frame. */
-	.cfi_def_cfa		%rbp, 16
-
 .Linvalid_input:
+	CFI_DEF_CFA		%rbp, 16
 	mov	$(-EINVAL), %eax
 	jmp	.Lout
 
-- 
2.47.2

[PATCH v5 6/6] x86/vdso: Enable sframe generation in VDSO

[Steven Rostedt]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Enable sframe generation in the VDSO library so kernel and user space
can unwind through it.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v4: https://lore.kernel.org/all/c93fbd53f01c2c86f747af27040ac11f16dee032.1737511963.git.jpoimboe@kernel.org/

- Changed #ifdef to include SFRAME config:
  #if defined(__x86_64__) && defined(CONFIG_AS_SFRAME)
  (Jens Remus)

- Fixed Makefile to use "ifeq" and not "#ifdef"
  (Jens Remus)

 arch/Kconfig                          |  3 +++
 arch/x86/entry/vdso/Makefile          | 10 +++++++---
 arch/x86/entry/vdso/vdso-layout.lds.S |  3 +++
 arch/x86/include/asm/dwarf2.h         |  5 ++++-
 4 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index b0adb665041f..6e7d739e853b 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -435,6 +435,9 @@ config HAVE_HARDLOCKUP_DETECTOR_ARCH
 	  It uses the same command line parameters, and sysctl interface,
 	  as the generic hardlockup detectors.
 
+config AS_SFRAME
+	def_bool $(as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc)
+
 config HAVE_PERF_REGS
 	bool
 	help
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 54d3e9774d62..3bab770337b3 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -47,13 +47,17 @@ quiet_cmd_vdso2c = VDSO2C  $@
 $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
 	$(call if_changed,vdso2c)
 
+ifeq ($(CONFIG_AS_SFRAME),y)
+  SFRAME_CFLAGS := -Wa$(comma)-gsframe
+endif
+
 #
 # Don't omit frame pointers for ease of userspace debugging, but do
 # optimize sibling calls.
 #
 CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
        $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
-       -fno-omit-frame-pointer -foptimize-sibling-calls \
+       -fno-omit-frame-pointer $(SFRAME_CFLAGS) -foptimize-sibling-calls \
        -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
 
 ifdef CONFIG_MITIGATION_RETPOLINE
@@ -63,7 +67,7 @@ endif
 endif
 
 $(vobjs): KBUILD_CFLAGS := $(filter-out $(PADDING_CFLAGS) $(CC_FLAGS_LTO) $(CC_FLAGS_CFI) $(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
-$(vobjs): KBUILD_AFLAGS += -DBUILD_VDSO
+$(vobjs): KBUILD_AFLAGS += -DBUILD_VDSO $(SFRAME_CFLAGS)
 
 #
 # vDSO code runs in userspace and -pg doesn't help with profiling anyway.
@@ -104,7 +108,7 @@ $(obj)/%-x32.o: $(obj)/%.o FORCE
 
 targets += vdsox32.lds $(vobjx32s-y)
 
-$(obj)/%.so: OBJCOPYFLAGS := -S --remove-section __ex_table
+$(obj)/%.so: OBJCOPYFLAGS := -g --remove-section __ex_table
 $(obj)/%.so: $(obj)/%.so.dbg FORCE
 	$(call if_changed,objcopy)
 
diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index 60747905de2b..24b92687597b 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -59,6 +59,7 @@ SECTIONS
 	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr
 	.eh_frame	: { KEEP (*(.eh_frame)) }	:text
 
+	.sframe		: { *(.sframe) }		:text	:sframe
 
 	/*
 	 * Text is well-separated from actual data: there's plenty of
@@ -87,6 +88,7 @@ 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
@@ -98,4 +100,5 @@ 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;
 }
diff --git a/arch/x86/include/asm/dwarf2.h b/arch/x86/include/asm/dwarf2.h
index 65d958ef1178..ce294e6c9017 100644
--- a/arch/x86/include/asm/dwarf2.h
+++ b/arch/x86/include/asm/dwarf2.h
@@ -12,8 +12,11 @@
 	 * For the vDSO, emit both runtime unwind information and debug
 	 * symbols for the .dbg file.
 	 */
-
+#if defined(__x86_64__) && defined(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
-- 
2.47.2

Re: [PATCH v5 3/6] x86/asm: Fix VDSO DWARF generation with kernel IBT enabled

[Josh Poimboeuf]

On Tue, Apr 22, 2025 at 02:34:42PM -0400, Steven Rostedt wrote:
> From: Josh Poimboeuf <jpoimboe@kernel.org>
> 
> The DWARF .cfi_startproc annotation needs to be at the very beginning of
> a function.  But with kernel IBT that doesn't happen as ENDBR is
> sneakily embedded in SYM_FUNC_START.  As a result the DWARF unwinding
> info is wrong at the beginning of all the VDSO functions.
> 
> Fix it by adding CFI_STARTPROC and CFI_ENDPROC to SYM_FUNC_START_* and
> SYM_FUNC_END respectively.  Note this only affects VDSO, as the CFI_*
> macros are empty for the kernel proper.
> 
> Fixes: c4691712b546 ("x86/linkage: Add ENDBR to SYM_FUNC_START*()")
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> [ Fixed rebased issues. May need extra review ]
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> Changes since v4: https://lore.kernel.org/all/5c7992c111adee94e242fbca2b3e64ab8e96e595.1737511963.git.jpoimboe@kernel.org/
> 
> - Rebased to latest kernel which had changes to the ENDBR caused by:
>   582077c94052 ("x86/cfi: Clean up linkage")

The code looks good, though that bug was already fixed up by
582077c94052 ("x86/cfi: Clean up linkage").  So this is really just a
cleanup now.  The "Fixes" tag can be removed, with the commit log
something like: 

Add CFI_STARTPROC and CFI_ENDPROC annotations to the SYM_FUNC_* macros
so the VDSO asm functions don't need to add them manually.  Note this
only affects VDSO, the CFI_* macros are empty for the kernel proper.

-- 
Josh

Re: [PATCH v5 6/6] x86/vdso: Enable sframe generation in VDSO

[Josh Poimboeuf]

On Tue, Apr 22, 2025 at 02:34:45PM -0400, Steven Rostedt wrote:
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -47,13 +47,17 @@ quiet_cmd_vdso2c = VDSO2C  $@
>  $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
>  	$(call if_changed,vdso2c)
>  
> +ifeq ($(CONFIG_AS_SFRAME),y)
> +  SFRAME_CFLAGS := -Wa$(comma)-gsframe
> +endif
> +

Based on the discussion with Jens on v4, I think the $(comma) can just
be an actual comma here.

-- 
Josh