Re: [PATCH V2 6/9] Support for DTrace USDT probes in x86_64 targets.

[jose.marchesi@oracle.com (Jose E. Marchesi)]

Hi Pedro.

Thanks for your suggestions.  I updated the patch addressing them.


    Support for DTrace USDT probes in x86_64 targets.
    
    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.
    
    gdb/ChangeLog:
    
      2014-10-17  Jose E. Marchesi  <jose.marchesi@oracle.com>
    
    	* amd64-linux-tdep.c (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.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index a2251a3..1bbe3c1 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,20 @@
 2014-10-17  Jose E. Marchesi  <jose.marchesi@oracle.com>
 
+	* amd64-linux-tdep.c (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.
+
+2014-10-17  Jose E. Marchesi  <jose.marchesi@oracle.com>
+
 	* breakpoint.c (BREAK_ARGS_HELP): help string updated to mention
 	the -probe-dtrace new vpossible value for PROBE_MODIFIER.
 	* configure.ac (CONFIG_OBS): dtrace-probe.o added if BFD can
diff --git a/gdb/amd64-linux-tdep.c b/gdb/amd64-linux-tdep.c
index edbb1b3..9fe68b9 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