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| author | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2018-04-25 19:35:26 +0300 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2018-05-07 22:12:38 +0300 |
| commit | 23a4d7fd34856da8218c4cfc23dba7a6ec0a423a (patch) | |
| tree | f6bf7c9d6e0f61af64bba6877562e63793b8e4c1 /arch/s390/kernel/asm-offsets.c | |
| parent | 97489e0663fa700d6e7febddc43b58df98d7bcda (diff) | |
| download | linux-23a4d7fd34856da8218c4cfc23dba7a6ec0a423a.tar.xz | |
s390/ftrace: use expoline for indirect branches
The return from the ftrace_stub, _mcount, ftrace_caller and
return_to_handler functions is done with "br %r14" and "br %r1".
These are indirect branches as well and need to use execute
trampolines for CONFIG_EXPOLINE=y.
The ftrace_caller function is a special case as it returns to the
start of a function and may only use %r0 and %r1. For a pre z10
machine the standard execute trampoline uses a LARL + EX to do
this, but this requires *two* registers in the range %r1..%r15.
To get around this the 'br %r1' located in the lowcore is used,
then the EX instruction does not need an address register.
But the lowcore trick may only be used for pre z14 machines,
with noexec=on the mapping for the first page may not contain
instructions. The solution for that is an ALTERNATIVE in the
expoline THUNK generated by 'GEN_BR_THUNK %r1' to switch to
EXRL, this relies on the fact that a machine that supports
noexec=on has EXRL as well.
Cc: stable@vger.kernel.org # 4.16
Fixes: f19fbd5ed6 ("s390: introduce execute-trampolines for branches")
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/kernel/asm-offsets.c')
| -rw-r--r-- | arch/s390/kernel/asm-offsets.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c index eb2a5c0443cd..11aea745a2a6 100644 --- a/arch/s390/kernel/asm-offsets.c +++ b/arch/s390/kernel/asm-offsets.c @@ -181,6 +181,7 @@ int main(void) OFFSET(__LC_MACHINE_FLAGS, lowcore, machine_flags); OFFSET(__LC_PREEMPT_COUNT, lowcore, preempt_count); OFFSET(__LC_GMAP, lowcore, gmap); + OFFSET(__LC_BR_R1, lowcore, br_r1_trampoline); /* software defined ABI-relevant lowcore locations 0xe00 - 0xe20 */ OFFSET(__LC_DUMP_REIPL, lowcore, ipib); /* hardware defined lowcore locations 0x1000 - 0x18ff */ |