Re: [PATCH V4 6/9] Support for DTrace USDT probes in x86_64 targets.

[Sergio Durigan Junior <sergiodj@redhat.com>]

On Monday, February 02 2015, Jose E. Marchesi wrote:

> This patch adds the target-specific code in order to support the
> calculation of DTrace probes arguments in x86_64 targets, and also the
> enabling and disabling of probes.  This is done by implementing the
> `dtrace_*' gdbarch handlers.

Thanks for the patch.  This was approved already; no further comments.  OK.

> gdb/ChangeLog:
>
> 2015-02-02  Jose E. Marchesi  <jose.marchesi@oracle.com>
>
> 	* amd64-linux-tdep.c: Include "parser-defs.h" and "user-regs.h".
> 	(amd64_dtrace_parse_probe_argument): New function.
> 	(amd64_dtrace_probe_is_enabled): Likewise.
> 	(amd64_dtrace_enable_probe): Likewise.
> 	(amd64_dtrace_disable_probe): Likewise.
> 	(amd64_linux_init_abi): Register the
> 	`gdbarch_dtrace_probe_argument', `gdbarch_dtrace_enable_probe',
> 	`gdbarch_dtrace_disable_probe' and
> 	`gdbarch_dtrace_probe_is_enabled' hooks.
> 	(amd64_dtrace_disabled_probe_sequence_1): New constant.
> 	(amd64_dtrace_disabled_probe_sequence_2): Likewise.
> 	(amd64_dtrace_enable_probe_sequence): Likewise.
> 	(amd64_dtrace_disable_probe_sequence): Likewise.
> ---
>  gdb/ChangeLog          |   16 ++++++
>  gdb/amd64-linux-tdep.c |  148 ++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 164 insertions(+)
>
> diff --git a/gdb/amd64-linux-tdep.c b/gdb/amd64-linux-tdep.c
> index 42d884e..ffa85f4 100644
> --- a/gdb/amd64-linux-tdep.c
> +++ b/gdb/amd64-linux-tdep.c
> @@ -28,6 +28,8 @@
>  #include "gdbtypes.h"
>  #include "reggroups.h"
>  #include "regset.h"
> +#include "parser-defs.h"
> +#include "user-regs.h"
>  #include "amd64-linux-tdep.h"
>  #include "i386-linux-tdep.h"
>  #include "linux-tdep.h"
> @@ -1643,6 +1645,146 @@ amd64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
>        &amd64_linux_xstateregset, "XSAVE extended state", cb_data);
>  }
>  
> +/* The instruction sequences used in x86_64 machines for a
> +   disabled is-enabled probe.  */
> +
> +const gdb_byte amd64_dtrace_disabled_probe_sequence_1[] = {
> +  /* xor %rax, %rax */  0x48, 0x33, 0xc0,
> +  /* nop            */  0x90,
> +  /* nop            */  0x90
> +};
> +
> +const gdb_byte amd64_dtrace_disabled_probe_sequence_2[] = {
> +  /* xor %rax, %rax */  0x48, 0x33, 0xc0,
> +  /* ret            */  0xc3,
> +  /* nop            */  0x90
> +};
> +
> +/* The instruction sequence used in x86_64 machines for enabling a
> +   DTrace is-enabled probe.  */
> +
> +const gdb_byte amd64_dtrace_enable_probe_sequence[] = {
> +  /* mov $0x1, %eax */ 0xb8, 0x01, 0x00, 0x00, 0x00
> +};
> +
> +/* The instruction sequence used in x86_64 machines for disabling a
> +   DTrace is-enabled probe.  */
> +
> +const gdb_byte amd64_dtrace_disable_probe_sequence[] = {
> +  /* xor %rax, %rax; nop; nop */ 0x48, 0x33, 0xC0, 0x90, 0x90
> +};
> +
> +/* Implementation of `gdbarch_dtrace_probe_is_enabled', as defined in
> +   gdbarch.h.  */
> +
> +static int
> +amd64_dtrace_probe_is_enabled (struct gdbarch *gdbarch, CORE_ADDR addr)
> +{
> +  gdb_byte buf[5];
> +
> +  /* This function returns 1 if the instructions at ADDR do _not_
> +     follow any of the amd64_dtrace_disabled_probe_sequence_*
> +     patterns.
> +
> +     Note that ADDR is offset 3 bytes from the beginning of these
> +     sequences.  */
> +  
> +  read_code (addr - 3, buf, 5);
> +  return (memcmp (buf, amd64_dtrace_disabled_probe_sequence_1, 5) != 0
> +	  && memcmp (buf, amd64_dtrace_disabled_probe_sequence_2, 5) != 0);
> +}
> +
> +/* Implementation of `gdbarch_dtrace_enable_probe', as defined in
> +   gdbarch.h.  */
> +
> +static void
> +amd64_dtrace_enable_probe (struct gdbarch *gdbarch, CORE_ADDR addr)
> +{
> +  /* Note also that ADDR is offset 3 bytes from the beginning of
> +     amd64_dtrace_enable_probe_sequence.  */
> +
> +  write_memory (addr - 3, amd64_dtrace_enable_probe_sequence, 5);
> +}
> +
> +/* Implementation of `gdbarch_dtrace_disable_probe', as defined in
> +   gdbarch.h.  */
> +
> +static void
> +amd64_dtrace_disable_probe (struct gdbarch *gdbarch, CORE_ADDR addr)
> +{
> +  /* Note also that ADDR is offset 3 bytes from the beginning of
> +     amd64_dtrace_disable_probe_sequence.  */
> +
> +  write_memory (addr - 3, amd64_dtrace_disable_probe_sequence, 5);
> +}
> +
> +/* Implementation of `gdbarch_dtrace_parse_probe_argument', as defined
> +   in gdbarch.h.  */
> +
> +static void
> +amd64_dtrace_parse_probe_argument (struct gdbarch *gdbarch,
> +				   struct parser_state *pstate,
> +				   int narg)
> +{
> +  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
> +  struct frame_info *this_frame = get_selected_frame (NULL);
> +  struct stoken str;
> +
> +  /* DTrace probe arguments can be found on the ABI-defined places for
> +     regular arguments at the current PC.  The probe abstraction
> +     currently supports up to 12 arguments for probes.  */
> +
> +  if (narg < 6)
> +    {
> +      static const int arg_reg_map[6] =
> +	{
> +	  AMD64_RDI_REGNUM,  /* Arg 1.  */
> +	  AMD64_RSI_REGNUM,  /* Arg 2.  */
> +	  AMD64_RDX_REGNUM,  /* Arg 3.  */
> +	  AMD64_RCX_REGNUM,  /* Arg 4.  */
> +	  AMD64_R8_REGNUM,   /* Arg 5.  */
> +	  AMD64_R9_REGNUM    /* Arg 6.  */
> +	};
> +      int regno = arg_reg_map[narg];
> +      const char *regname = user_reg_map_regnum_to_name (gdbarch, regno);
> +
> +      write_exp_elt_opcode (pstate, OP_REGISTER);
> +      str.ptr = regname;
> +      str.length = strlen (regname);
> +      write_exp_string (pstate, str);
> +      write_exp_elt_opcode (pstate, OP_REGISTER);
> +    }
> +  else
> +    {
> +      /* Additional arguments are passed on the stack.  */
> +      CORE_ADDR sp;
> +      const char *regname = user_reg_map_regnum_to_name (gdbarch, AMD64_RSP_REGNUM);
> +
> +      /* Displacement.  */
> +      write_exp_elt_opcode (pstate, OP_LONG);
> +      write_exp_elt_type (pstate, builtin_type (gdbarch)->builtin_long);
> +      write_exp_elt_longcst (pstate, narg - 6);
> +      write_exp_elt_opcode (pstate, OP_LONG);
> +
> +      /* Register: SP.  */
> +      write_exp_elt_opcode (pstate, OP_REGISTER);
> +      str.ptr = regname;
> +      str.length = strlen (regname);
> +      write_exp_string (pstate, str);
> +      write_exp_elt_opcode (pstate, OP_REGISTER);
> +
> +      write_exp_elt_opcode (pstate, BINOP_ADD);
> +
> +      /* Cast to long. */
> +      write_exp_elt_opcode (pstate, UNOP_CAST);
> +      write_exp_elt_type (pstate,
> +			  lookup_pointer_type (builtin_type (gdbarch)->builtin_long));
> +      write_exp_elt_opcode (pstate, UNOP_CAST);
> +
> +      write_exp_elt_opcode (pstate, UNOP_IND);
> +    }
> +}
> +
>  static void
>  amd64_linux_init_abi_common(struct gdbarch_info info, struct gdbarch *gdbarch)
>  {
> @@ -1907,6 +2049,12 @@ amd64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
>    /* GNU/Linux uses SVR4-style shared libraries.  */
>    set_solib_svr4_fetch_link_map_offsets
>      (gdbarch, svr4_lp64_fetch_link_map_offsets);
> +
> +  /* Register DTrace handlers.  */
> +  set_gdbarch_dtrace_parse_probe_argument (gdbarch, amd64_dtrace_parse_probe_argument);
> +  set_gdbarch_dtrace_probe_is_enabled (gdbarch, amd64_dtrace_probe_is_enabled);
> +  set_gdbarch_dtrace_enable_probe (gdbarch, amd64_dtrace_enable_probe);
> +  set_gdbarch_dtrace_disable_probe (gdbarch, amd64_dtrace_disable_probe);
>  }
>  
>  static void
> -- 
> 1.7.10.4

-- 
Sergio
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