Re: [PATCH trace-cmd] plugin_kvm: disassemble instructions for kvm_emulate_insn

[Steven Rostedt <rostedt@goodmis.org>]

On Sun, 2010-09-19 at 16:33 +0200, Avi Kivity wrote:
> Override kvm_emulate_insn formatting to use a disassembler to format
> the emulated instruction.  If a disassembler (udis86) is not available,
> fall back to showing the instruction bytes in hex.
> 
> Signed-off-by: Avi Kivity <avi@redhat.com>
> ---
> 
> Note 1: on top of 'master' with 'trace-cmd-kvm' cherry-picked on top.

Thanks, I merged trace-cmd-kvm into master and applied your patch
(haven't pushed yet).


> 
> Note 2: I get output of the form
> 
> ... kvm_emulate_insn:     0:fffff800010527b5: mov $0x0, 0xfffe00b0CAN'T FIND FIELD "guest_rip"
> 
> which leads me to believe there is a bug in trace_seq_printf when the input
> to %s is "".

I ran this under gdb (nice to do that, where I don't in kernel :-)  And
it takes me to kvm_emulate_insn_handler() which does the
trace_seq_printf() fine, but then calls pevent_print_num_field() and
that passes in "guest_rip" where we get the "CAN'T FIND FIELD" error.

In pevent_print_num_field() it searches for "guest_rip" at the top of
the function (pevent_find_field()), but the event kvm_emulate_insn does
not have a "guest_rip" field, then it jumps to the error message.

-- Steve

> 
>  Makefile     |   11 +++++-
>  plugin_kvm.c |  111 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 121 insertions(+), 1 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 5282f94..fe34d1c 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -74,6 +74,14 @@ ifeq ($(shell sh -c "python-config --includes > /dev/null 2>&1 && echo y"), y)
>  	PYTHON_PY_INSTALL := event-viewer.install tracecmd.install tracecmdgui.install
>  endif
>  
> +# $(call test-build, snippet, ret) -> ret if snippet compiles
> +#                                  -> empty otherwise
> +test-build = $(if $(shell $(CC) -o /dev/null -c -x c - > /dev/null 2>&1 \
> +	                  <<<'$1' && echo y), $2)
> +
> +# have udis86 disassembler library?
> +udis86-flags := $(call test-build,\#include <udis86.h>,-DHAVE_UDIS86 -ludis86)
> +
>  ifeq ("$(origin O)", "command line")
>    BUILD_OUTPUT := $(O)
>  endif
> @@ -188,6 +196,7 @@ CFLAGS ?= -g -Wall
>  
>  # Append required CFLAGS
>  override CFLAGS += $(CONFIG_FLAGS) $(INCLUDES) $(PLUGIN_DIR_SQ)
> +override CFLAGS += $(udis86-flags)
>  
>  ifeq ($(VERBOSE),1)
>    Q =
> @@ -228,7 +237,7 @@ do_compile_plugin_obj =				\
>  
>  do_plugin_build =				\
>  	($(print_plugin_build)			\
> -	$(CC) -shared -nostartfiles -o $@ $<)
> +	$(CC) $(CFLAGS) -shared -nostartfiles -o $@ $<)
>  
>  do_build_static_lib =				\
>  	($(print_static_lib_build)		\
> diff --git a/plugin_kvm.c b/plugin_kvm.c
> index 7217e85..00cac5a 100644
> --- a/plugin_kvm.c
> +++ b/plugin_kvm.c
> @@ -21,9 +21,68 @@
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <string.h>
> +#include <stdint.h>
>  
>  #include "parse-events.h"
>  
> +#ifdef HAVE_UDIS86
> +
> +#include <udis86.h>
> +
> +static ud_t ud;
> +
> +static void init_disassembler(void)
> +{
> +	ud_init(&ud);
> +	ud_set_syntax(&ud, UD_SYN_ATT);
> +}
> +
> +static const char *disassemble(unsigned char *insn, int len, uint64_t rip,
> +			       int cr0_pe, int eflags_vm,
> +			       int cs_d, int cs_l)
> +{
> +	int mode;
> +
> +	if (!cr0_pe)
> +		mode = 16;
> +	else if (eflags_vm)
> +		mode = 16;
> +	else if (cs_l)
> +		mode = 64;
> +	else if (cs_d)
> +		mode = 32;
> +	else
> +		mode = 16;
> +
> +	ud_set_pc(&ud, rip);
> +	ud_set_mode(&ud, mode);
> +	ud_set_input_buffer(&ud, insn, len);
> +	ud_disassemble(&ud);
> +	return ud_insn_asm(&ud);
> +}
> +
> +#else
> +
> +static void init_disassembler(void)
> +{
> +}
> +
> +static const char *disassemble(unsigned char *insn, int len, uint64_t rip,
> +			       int cr0_pe, int eflags_vm,
> +			       int cs_d, int cs_l)
> +{
> +	static char out[15*3+1];
> +	int i;
> +
> +	for (i = 0; i < len; ++i)
> +		sprintf(out + i * 3, "%02x ", insn[i]);
> +	out[len*3-1] = '\0';
> +	return out;
> +}
> +
> +#endif
> +
> +
>  #define VMX_EXIT_REASONS			\
>  	_ER(EXCEPTION_NMI,	0)		\
>  	_ER(EXTERNAL_INTERRUPT,	1)		\
> @@ -99,6 +158,53 @@ static int kvm_exit_handler(struct trace_seq *s, struct record *record,
>  	return 0;
>  }
>  
> +#define KVM_EMUL_INSN_F_CR0_PE (1 << 0)
> +#define KVM_EMUL_INSN_F_EFL_VM (1 << 1)
> +#define KVM_EMUL_INSN_F_CS_D   (1 << 2)
> +#define KVM_EMUL_INSN_F_CS_L   (1 << 3)
> +
> +static int kvm_emulate_insn_handler(struct trace_seq *s, struct record *record,
> +				    struct event_format *event, void *context)
> +{
> +	unsigned long long rip, csbase, len, flags, failed;
> +	int llen;
> +	uint8_t *insn;
> +	const char *disasm;
> +
> +	if (pevent_get_field_val(s, event, "rip", record, &rip, 1) < 0)
> +		return -1;
> +
> +	if (pevent_get_field_val(s, event, "csbase", record, &csbase, 1) < 0)
> +		return -1;
> +
> +	if (pevent_get_field_val(s, event, "len", record, &len, 1) < 0)
> +		return -1;
> +
> +	if (pevent_get_field_val(s, event, "flags", record, &flags, 1) < 0)
> +		return -1;
> +
> +	if (pevent_get_field_val(s, event, "failed", record, &failed, 1) < 0)
> +		return -1;
> +
> +	insn = pevent_get_field_raw(s, event, "insn", record, &llen, 1);
> +	if (!insn)
> +		return -1;
> +
> +	disasm = disassemble(insn, len, rip,
> +			     flags & KVM_EMUL_INSN_F_CR0_PE,
> +			     flags & KVM_EMUL_INSN_F_EFL_VM,
> +			     flags & KVM_EMUL_INSN_F_CS_D,
> +			     flags & KVM_EMUL_INSN_F_CS_L);
> +
> +	trace_seq_printf(s, "%llx:%llx: %s%s", csbase, rip, disasm,
> +			 failed ? " FAIL" : "");
> +
> +	pevent_print_num_field(s, " rip %0xlx", event, "guest_rip", record, 1);
> +
> +	return 0;
> +}
> +
> +
>  static int kvm_nested_vmexit_inject_handler(struct trace_seq *s, struct record *record,
>  					    struct event_format *event, void *context)
>  {
> @@ -199,9 +305,14 @@ static int kvm_mmu_get_page_handler(struct trace_seq *s, struct record *record,
>  
>  int PEVENT_PLUGIN_LOADER(struct pevent *pevent)
>  {
> +	init_disassembler();
> +
>  	pevent_register_event_handler(pevent, -1, "kvm", "kvm_exit",
>  				      kvm_exit_handler, NULL);
>  
> +	pevent_register_event_handler(pevent, -1, "kvm", "kvm_emulate_insn",
> +				      kvm_emulate_insn_handler, NULL);
> +
>  	pevent_register_event_handler(pevent, -1, "kvm", "kvm_nested_vmexit",
>  				      kvm_nested_vmexit_handler, NULL);
>