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Subject[RFC PATCH 0/6] jump label v3
hi,

Refresh of the jump labeling patches. We introduce the following:

# ifdef CONFIG_X86_64
# define JUMP_LABEL_NOP P6_NOP5
# else
# define JUMP_LABEL_NOP ".byte 0xe9 \n\t .long 0\n\t"
# endif

# define JUMP_LABEL(tag, label, cond) \
do { \
static const char __jlstrtab_##tag[] \
__used __attribute__((section("__jump_strings"))) = #tag; \
asm goto("1:" \
JUMP_LABEL_NOP \
".pushsection __jump_table, \"a\" \n\t" \
_ASM_PTR "1b, %l[" #label "], %c0 \n\t" \
".popsection \n\t" \
: : "i" (__jlstrtab_##tag) : : label); \
} while (0)
-------------
I'm using an atomic 5 byte no-op for x86_64 and a long jump for 32-bit x86.
My understanding is that not all 32-bit processors have an atomic 5 byte no-op,
and thus using a long jump or jump 0, for the off case is the safest.

which can then be used by the tracepoint code as:

#define DECLARE_TRACE(name, proto, args) \
extern struct tracepoint __tracepoint_##name; \
static inline void trace_##name(proto) \
{ \
JUMP_LABEL(name, do_trace, __tracepoint_##name.state); \
return; \
do_trace: \
__DO_TRACE(&__tracepoint_##name, \
TP_PROTO(proto), TP_ARGS(args)); \

--------------
Thus, in the disabled tracing case we have a no-op followed by a jump around
the disabled code. When we enable the tracepoint, we simply patch the no-op
with a jump to the 'do_trace' label. This relies on the 'asm goto' construct
which is already merged into gcc 4.5. In subsequent gcc versions, we also hope
to make use of 'cold' label for the 'do_trace' section. Thus, making the
disabled or straight line codepath, simply a no-op.

As discussed in pervious mails I've seen an average improvement of 30 cycles
per-tracepoint on x86_64 systems that I've tested.

The first 2 patches of the series are a repost of Masami's text_poke_fixup()
function, which allows for efficient instruction patching. The final 4 patches,
implement the the jump patching mechanism for x86 and x86_64.

The implementation is a 'low' level one, in the sense that it is geared
specifically for tracepoints. However, I believe this mechanism will be more
generally useful for other parts of the kernel. Thus, I will propose 'higher'
level interfaces into the jump label code (layered on these 'low' level ones),
as we go.

thanks,

-Jason

Masami Hiramatsu (2):
x86: Introduce generic jump patching without stop_machine
kprobes/x86: Cleanup RELATIVEJUMP_INSTRUCTION to RELATIVEJUMP_OPCODE

Jason Baron(4):
move opcode defs from asm/kprobes.h to asm/alternative.h
jump-label-basic
jump-module-support
jump-label-tracepoints

arch/x86/include/asm/alternative.h | 17 +++++
arch/x86/include/asm/jump_label.h | 35 +++++++++++
arch/x86/include/asm/kprobes.h | 3 -
arch/x86/kernel/Makefile | 2 +-
arch/x86/kernel/alternative.c | 120 ++++++++++++++++++++++++++++++++++++
arch/x86/kernel/jump_label.c | 66 ++++++++++++++++++++
arch/x86/kernel/kprobes.c | 2 +-
include/asm-generic/vmlinux.lds.h | 11 +++-
include/linux/jump_label.h | 47 ++++++++++++++
include/linux/module.h | 12 +++-
include/linux/tracepoint.h | 35 ++++++-----
kernel/kprobes.c | 2 +-
kernel/module.c | 27 ++++++++-
kernel/tracepoint.c | 25 ++++++--
14 files changed, 372 insertions(+), 32 deletions(-)
create mode 100644 arch/x86/include/asm/jump_label.h
create mode 100644 arch/x86/kernel/jump_label.c
create mode 100644 include/linux/jump_label.h


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