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s390/vdso: revise CFI annotations of vDSO functions

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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>
This commit is contained in:
Hendrik Brueckner
2017-11-20 11:46:13 +01:00
committed by Martin Schwidefsky
parent bc3703f21c
commit 7bceec4e58
10 changed files with 69 additions and 18 deletions
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16
arch/s390/kernel/vdso32/clock_gettime.S
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@@ -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