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| author | Heiko Carstens <heiko.carstens@de.ibm.com> | 2014-10-15 12:17:38 +0200 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2014-10-27 13:27:27 +0100 |
| commit | c933146a5e41e42ea3eb4f34fa02e201da3f068e (patch) | |
| tree | b5c108df5c2e4756e2c4fc2014a83663bdaba549 /arch/s390/include/asm/lowcore.h | |
| parent | f7f242ff004499e0904d3664713dfba01f24c408 (diff) | |
| download | linux-c933146a5e41e42ea3eb4f34fa02e201da3f068e.tar.gz linux-c933146a5e41e42ea3eb4f34fa02e201da3f068e.tar.bz2 linux-c933146a5e41e42ea3eb4f34fa02e201da3f068e.zip | |
s390/ftrace,kprobes: allow to patch first instruction
If the function tracer is enabled, allow to set kprobes on the first
instruction of a function (which is the function trace caller):
If no kprobe is set handling of enabling and disabling function tracing
of a function simply patches the first instruction. Either it is a nop
(right now it's an unconditional branch, which skips the mcount block),
or it's a branch to the ftrace_caller() function.
If a kprobe is being placed on a function tracer calling instruction
we encode if we actually have a nop or branch in the remaining bytes
after the breakpoint instruction (illegal opcode).
This is possible, since the size of the instruction used for the nop
and branch is six bytes, while the size of the breakpoint is only
two bytes.
Therefore the first two bytes contain the illegal opcode and the last
four bytes contain either "0" for nop or "1" for branch. The kprobes
code will then execute/simulate the correct instruction.
Instruction patching for kprobes and function tracer is always done
with stop_machine(). Therefore we don't have any races where an
instruction is patched concurrently on a different cpu.
Besides that also the program check handler which executes the function
trace caller instruction won't be executed concurrently to any
stop_machine() execution.
This allows to keep full fault based kprobes handling which generates
correct pt_regs contents automatically.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/include/asm/lowcore.h')
| -rw-r--r-- | arch/s390/include/asm/lowcore.h | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h index 6cc51fe84410..34fbcac61133 100644 --- a/arch/s390/include/asm/lowcore.h +++ b/arch/s390/include/asm/lowcore.h @@ -147,7 +147,7 @@ struct _lowcore { __u32 softirq_pending; /* 0x02ec */ __u32 percpu_offset; /* 0x02f0 */ __u32 machine_flags; /* 0x02f4 */ - __u32 ftrace_func; /* 0x02f8 */ + __u8 pad_0x02f8[0x02fc-0x02f8]; /* 0x02f8 */ __u32 spinlock_lockval; /* 0x02fc */ __u8 pad_0x0300[0x0e00-0x0300]; /* 0x0300 */ @@ -297,7 +297,7 @@ struct _lowcore { __u64 percpu_offset; /* 0x0378 */ __u64 vdso_per_cpu_data; /* 0x0380 */ __u64 machine_flags; /* 0x0388 */ - __u64 ftrace_func; /* 0x0390 */ + __u8 pad_0x0390[0x0398-0x0390]; /* 0x0390 */ __u64 gmap; /* 0x0398 */ __u32 spinlock_lockval; /* 0x03a0 */ __u8 pad_0x03a0[0x0400-0x03a4]; /* 0x03a4 */ |