s390/vdso: revise CFI annotations of vDSO functions

Revise and add CFI CFA and register rule annotations to the vDSO
functions for proper stack unwinding and debugging.

Because glibc might call the vDSO in special ways, the vDSO code
does not rely on a stack frame created by the caller.  The TOD clock
value can be therefore not stored in the pre-allocated stack area
and additional stack space is required.
To correctly annotate these situations with CFI, the .cfi_val_offset
directive is required to create relative offsets on the value of the
stack register %r15.  Because the .cfi_val_offset directive is
available with recent GNU assembler versions only, additional checks
are necessary.

Note that if the vDSO is assembled with an older assembler version,
stack unwinding and debugging from within the vDSO code might not
be possible.
Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Makefile

@@ -88,10 +88,13 @@ KBUILD_CFLAGS	+= -DCC_USING_HOTPATCH
 endif
 endif
 
+# Test CFI features of binutils
+cfi := $(call as-instr,.cfi_startproc\n.cfi_val_offset 15$(comma)-160\n.cfi_endproc,-DCONFIG_AS_CFI_VAL_OFFSET=1)
+
 KBUILD_CFLAGS	+= -mbackchain -msoft-float $(cflags-y)
 KBUILD_CFLAGS	+= -pipe -fno-strength-reduce -Wno-sign-compare
-KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables
-KBUILD_AFLAGS	+= $(aflags-y)
+KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables $(cfi)
+KBUILD_AFLAGS	+= $(aflags-y) $(cfi)
 
 OBJCOPYFLAGS	:= -O binary
 

arch/s390/include/asm/dwarf.h

@@ -4,6 +4,18 @@
 
 #ifdef __ASSEMBLY__
 
+#define CFI_STARTPROC		.cfi_startproc
+#define CFI_ENDPROC		.cfi_endproc
+#define CFI_DEF_CFA_OFFSET	.cfi_def_cfa_offset
+#define CFI_ADJUST_CFA_OFFSET	.cfi_adjust_cfa_offset
+#define CFI_RESTORE		.cfi_restore
+
+#ifdef CONFIG_AS_CFI_VAL_OFFSET
+#define CFI_VAL_OFFSET		.cfi_val_offset
+#else
+#define CFI_VAL_OFFSET		#
+#endif
+
 #ifndef BUILD_VDSO
 	/*
 	 * Emit CFI data in .debug_frame sections and not in .eh_frame

arch/s390/kernel/vdso32/clock_getres.S

@@ -16,7 +16,7 @@
 	.globl __kernel_clock_getres
 	.type  __kernel_clock_getres,@function
 __kernel_clock_getres:
-	.cfi_startproc
+	CFI_STARTPROC
 	basr	%r1,0
 	la	%r1,4f-.(%r1)
 	chi	%r2,__CLOCK_REALTIME
@@ -38,7 +38,7 @@ __kernel_clock_getres:
 3:	lhi	%r1,__NR_clock_getres		/* fallback to svc */
 	svc	0
 	br	%r14
+	CFI_ENDPROC
 4:	.long	__CLOCK_REALTIME_RES
 5:	.long	__CLOCK_COARSE_RES
-	.cfi_endproc
 	.size	__kernel_clock_getres,.-__kernel_clock_getres

arch/s390/kernel/vdso32/clock_gettime.S

@@ -16,8 +16,10 @@
 	.globl __kernel_clock_gettime
 	.type  __kernel_clock_gettime,@function
 __kernel_clock_gettime:
-	.cfi_startproc
+	CFI_STARTPROC
 	ahi	%r15,-16
+	CFI_DEF_CFA_OFFSET 176
+	CFI_VAL_OFFSET 15, -160
 	basr	%r5,0
 0:	al	%r5,21f-0b(%r5)			/* get &_vdso_data */
 	chi	%r2,__CLOCK_REALTIME_COARSE
@@ -70,9 +72,13 @@ __kernel_clock_gettime:
 	st	%r1,4(%r3)			/* store tp->tv_nsec */
 	lhi	%r2,0
 	ahi	%r15,16
+	CFI_DEF_CFA_OFFSET 160
+	CFI_RESTORE 15
 	br	%r14
 
 	/* CLOCK_MONOTONIC_COARSE */
+	CFI_DEF_CFA_OFFSET 176
+	CFI_VAL_OFFSET 15, -160
 9:	l	%r4,__VDSO_UPD_COUNT+4(%r5)	/* load update counter */
 	tml	%r4,0x0001			/* pending update ? loop */
 	jnz	9b
@@ -152,15 +158,21 @@ __kernel_clock_gettime:
 	st	%r1,4(%r3)			/* store tp->tv_nsec */
 	lhi	%r2,0
 	ahi	%r15,16
+	CFI_DEF_CFA_OFFSET 160
+	CFI_RESTORE 15
 	br	%r14
 
 	/* Fallback to system call */
+	CFI_DEF_CFA_OFFSET 176
+	CFI_VAL_OFFSET 15, -160
 19:	lhi	%r1,__NR_clock_gettime
 	svc	0
 	ahi	%r15,16
+	CFI_DEF_CFA_OFFSET 160
+	CFI_RESTORE 15
 	br	%r14
+	CFI_ENDPROC
 
 20:	.long	1000000000
 21:	.long	_vdso_data - 0b
-	.cfi_endproc
 	.size	__kernel_clock_gettime,.-__kernel_clock_gettime

arch/s390/kernel/vdso32/getcpu.S

@@ -15,7 +15,7 @@
 	.globl __kernel_getcpu
 	.type  __kernel_getcpu,@function
 __kernel_getcpu:
-	.cfi_startproc
+	CFI_STARTPROC
 	la	%r4,0
 	sacf	256
 	l	%r5,__VDSO_CPU_NR(%r4)
@@ -29,5 +29,5 @@ __kernel_getcpu:
 	st	%r4,0(%r3)
 3:	lhi	%r2,0
 	br	%r14
-	.cfi_endproc
+	CFI_ENDPROC
 	.size	__kernel_getcpu,.-__kernel_getcpu

arch/s390/kernel/vdso32/gettimeofday.S

@@ -16,8 +16,10 @@
 	.globl __kernel_gettimeofday
 	.type  __kernel_gettimeofday,@function
 __kernel_gettimeofday:
-	.cfi_startproc
+	CFI_STARTPROC
 	ahi	%r15,-16
+	CFI_ADJUST_CFA_OFFSET 16
+	CFI_VAL_OFFSET 15, -160
 	basr	%r5,0
 0:	al	%r5,13f-0b(%r5)			/* get &_vdso_data */
 1:	ltr	%r3,%r3				/* check if tz is NULL */
@@ -90,9 +92,11 @@ __kernel_gettimeofday:
 	st	%r0,4(%r2)			/* store tv->tv_usec */
 10:	slr	%r2,%r2
 	ahi	%r15,16
+	CFI_ADJUST_CFA_OFFSET -16
+	CFI_RESTORE 15
 	br	%r14
+	CFI_ENDPROC
 11:	.long	1000000000
 12:	.long	274877907
 13:	.long	_vdso_data - 0b
-	.cfi_endproc
 	.size	__kernel_gettimeofday,.-__kernel_gettimeofday

arch/s390/kernel/vdso64/clock_getres.S

@@ -16,7 +16,7 @@
 	.globl __kernel_clock_getres
 	.type  __kernel_clock_getres,@function
 __kernel_clock_getres:
-	.cfi_startproc
+	CFI_STARTPROC
 	larl	%r1,4f
 	cghi	%r2,__CLOCK_REALTIME_COARSE
 	je	0f
@@ -44,7 +44,7 @@ __kernel_clock_getres:
 2:	lghi	%r1,__NR_clock_getres		/* fallback to svc */
 	svc	0
 	br	%r14
+	CFI_ENDPROC
 3:	.quad	__CLOCK_REALTIME_RES
 4:	.quad	__CLOCK_COARSE_RES
-	.cfi_endproc
 	.size	__kernel_clock_getres,.-__kernel_clock_getres

arch/s390/kernel/vdso64/clock_gettime.S

@@ -16,8 +16,10 @@
 	.globl __kernel_clock_gettime
 	.type  __kernel_clock_gettime,@function
 __kernel_clock_gettime:
-	.cfi_startproc
+	CFI_STARTPROC
 	aghi	%r15,-16
+	CFI_DEF_CFA_OFFSET 176
+	CFI_VAL_OFFSET 15, -160
 	larl	%r5,_vdso_data
 	cghi	%r2,__CLOCK_REALTIME_COARSE
 	je	4f
@@ -54,9 +56,13 @@ __kernel_clock_gettime:
 	stg	%r1,8(%r3)			/* store tp->tv_nsec */
 	lghi	%r2,0
 	aghi	%r15,16
+	CFI_DEF_CFA_OFFSET 160
+	CFI_RESTORE 15
 	br	%r14
 
 	/* CLOCK_MONOTONIC_COARSE */
+	CFI_DEF_CFA_OFFSET 176
+	CFI_VAL_OFFSET 15, -160
 3:	lg	%r4,__VDSO_UPD_COUNT(%r5)	/* load update counter */
 	tmll	%r4,0x0001			/* pending update ? loop */
 	jnz	3b
@@ -109,9 +115,13 @@ __kernel_clock_gettime:
 	stg	%r1,8(%r3)			/* store tp->tv_nsec */
 	lghi	%r2,0
 	aghi	%r15,16
+	CFI_DEF_CFA_OFFSET 160
+	CFI_RESTORE 15
 	br	%r14
 
 	/* CPUCLOCK_VIRT for this thread */
+	CFI_DEF_CFA_OFFSET 176
+	CFI_VAL_OFFSET 15, -160
 9:	lghi	%r4,0
 	icm	%r0,15,__VDSO_ECTG_OK(%r5)
 	jz	12f
@@ -132,15 +142,21 @@ __kernel_clock_gettime:
 	stg	%r4,8(%r3)
 	lghi	%r2,0
 	aghi	%r15,16
+	CFI_DEF_CFA_OFFSET 160
+	CFI_RESTORE 15
 	br	%r14
 
 	/* Fallback to system call */
+	CFI_DEF_CFA_OFFSET 176
+	CFI_VAL_OFFSET 15, -160
 12:	lghi	%r1,__NR_clock_gettime
 	svc	0
 	aghi	%r15,16
+	CFI_DEF_CFA_OFFSET 160
+	CFI_RESTORE 15
 	br	%r14
+	CFI_ENDPROC
 
 13:	.quad	1000000000
 14:	.quad	19342813113834067
-	.cfi_endproc
 	.size	__kernel_clock_gettime,.-__kernel_clock_gettime

arch/s390/kernel/vdso64/getcpu.S

@@ -15,7 +15,7 @@
 	.globl __kernel_getcpu
 	.type  __kernel_getcpu,@function
 __kernel_getcpu:
-	.cfi_startproc
+	CFI_STARTPROC
 	la	%r4,0
 	sacf	256
 	l	%r5,__VDSO_CPU_NR(%r4)
@@ -29,5 +29,5 @@ __kernel_getcpu:
 	st	%r4,0(%r3)
 3:	lghi	%r2,0
 	br	%r14
-	.cfi_endproc
+	CFI_ENDPROC
 	.size	__kernel_getcpu,.-__kernel_getcpu

arch/s390/kernel/vdso64/gettimeofday.S

@@ -16,8 +16,10 @@
 	.globl __kernel_gettimeofday
 	.type  __kernel_gettimeofday,@function
 __kernel_gettimeofday:
-	.cfi_startproc
+	CFI_STARTPROC
 	aghi	%r15,-16
+	CFI_ADJUST_CFA_OFFSET 16
+	CFI_VAL_OFFSET 15, -160
 	larl	%r5,_vdso_data
 0:	ltgr	%r3,%r3				/* check if tz is NULL */
 	je	1f
@@ -59,8 +61,10 @@ __kernel_gettimeofday:
 	stg	%r0,8(%r2)			/* store tv->tv_usec */
 4:	lghi	%r2,0
 	aghi	%r15,16
+	CFI_ADJUST_CFA_OFFSET -16
+	CFI_RESTORE 15
 	br	%r14
+	CFI_ENDPROC
 5:	.quad	1000000000
 	.long	274877907
-	.cfi_endproc
 	.size	__kernel_gettimeofday,.-__kernel_gettimeofday