[PATCH v2 0/2] s390 vs. kprobes on ftrace

Heiko Carstens
2014-10-20T11:00:10Z

v2:
Changed patch 1/2 to incorporate feedback from Masami Hiramatsu, and
introduce a new helper function check_ftrace_location().
The requested ftracetest has been sent as an own patch set, since it
has no dependency to these patches.

v1:
We would like to implement an architecture specific variant of "kprobes
on ftrace" without using the current HAVE_KPROBES_ON_FTRACE infrastructure
which is currently only used by x86.

The rationale for these two patches is:
- we want to patch the first instruction of the mcount code block to
reduce the overhead of the function tracer
- we'd like to keep the ftrace_caller function as simple as possible and
not require it to generate a 100% valid pt_regs structure as required
by the combination of DYNAMIC_FTRACE_WITH_REGS and HAVE_KPROBES_ON_FTRACE.
This allows us to not generate the psw mask field in the pt_regs
structure on each function tracer enabled function, which otherwise would
be very expensive. Besides that program check generated pt_regs contents
are "more" accurate than program generated ones and don't require any
maintenance.
And also we can keep the ftrace and kprobes backends quite separated.

In order to make this work a small common code change is necessary which
removes a check if kprobe is being placed on an ftrace location (see
first patch).

If possible, I'd like to have an ACK from at least one of the kprobes
maintainers for the first patch and bring it upstream via the s390 tree.

Thanks,
Heiko

Heiko Carstens (2):
kprobes: introduce ARCH_HANDLES_KPROBES_ON_FTRACE
s390/ftrace,kprobes: allow to patch first instruction

arch/Kconfig | 8 +++
arch/s390/Kconfig | 1 +
arch/s390/include/asm/ftrace.h | 52 ++++++++++++++--
arch/s390/include/asm/kprobes.h | 1 +
arch/s390/include/asm/lowcore.h | 4 +-
arch/s390/include/asm/pgtable.h | 12 ++++
arch/s390/kernel/asm-offsets.c | 1 -
arch/s390/kernel/early.c | 4 --
arch/s390/kernel/ftrace.c | 132 +++++++++++++++++++++++++---------------
arch/s390/kernel/kprobes.c | 87 ++++++++++++++++++--------
arch/s390/kernel/mcount.S | 1 +
arch/s390/kernel/setup.c | 2 -
arch/s390/kernel/smp.c | 1 -
kernel/kprobes.c | 36 ++++++-----
scripts/recordmcount.c | 2 +-
scripts/recordmcount.pl | 2 +-
16 files changed, 239 insertions(+), 107 deletions(-)

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1.8.5.5