[Lldb-commits] [lldb] r145357 - /lldb/trunk/docs/lldb-gdb-remote.txt

Greg Clayton gclayton at apple.com
Mon Nov 28 19:44:07 CST 2011


Author: gclayton
Date: Mon Nov 28 19:44:07 2011
New Revision: 145357

URL: http://llvm.org/viewvc/llvm-project?rev=145357&view=rev
Log:
I added more complete documentation on all of the new packets we use in LLDB
as well as attached a new priority description as to why and when you would
want to implement each packet.

Also documented the additions we have made to the stop reply packet and why
the extra information is necessary.


Modified:
    lldb/trunk/docs/lldb-gdb-remote.txt

Modified: lldb/trunk/docs/lldb-gdb-remote.txt
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/docs/lldb-gdb-remote.txt?rev=145357&r1=145356&r2=145357&view=diff
==============================================================================
--- lldb/trunk/docs/lldb-gdb-remote.txt (original)
+++ lldb/trunk/docs/lldb-gdb-remote.txt Mon Nov 28 19:44:07 2011
@@ -18,7 +18,13 @@
 //----------------------------------------------------------------------
 // "QStartNoAckMode"
 //
-// Try to enable no ACK mode to skip sending ACKs and NACKs.
+// BRIEF
+//  Try to enable no ACK mode to skip sending ACKs and NACKs.
+//
+// PRIORITY TO IMPLEMENT
+//  High. Any GDB remote server that can implement this should if the
+//  connection is reliable. This improves packet throughput and increases
+//  the performance of the connection.
 //----------------------------------------------------------------------
 Having to send an ACK/NACK after every packet slows things down a bit, so we
 have a way to disable ACK packets to mimize the traffic for reliable
@@ -37,7 +43,13 @@
 //----------------------------------------------------------------------
 // "A" - launch args packet
 //
-// Launch a program using the supplied arguments
+// BRIEF
+//  Launch a program using the supplied arguments
+//
+// PRIORITY TO IMPLEMENT
+//  Low. Only needed if the remote target wants to launch a target after
+//  making a connection to a GDB server that isn't already connected to
+//  an inferior process.
 //----------------------------------------------------------------------
 
 We have added support for the "set program arguments" packet where we can
@@ -46,7 +58,7 @@
 
 GDB remote docs for this:
 
-set program arguments(reserved)	Aarglen,argnum,arg,...
+set program arguments(reserved) Aarglen,argnum,arg,...
 
 Where A is followed by the length in bytes of the hex encoded argument,
 followed by an argument integer, and followed by the ASCII characters
@@ -62,8 +74,14 @@
 //----------------------------------------------------------------------
 // "QEnvironment:NAME=VALUE"
 //
-// Setup the environment up for a new child process that will soon be
-// launched using the "A" packet.
+// BRIEF
+//  Setup the environment up for a new child process that will soon be
+//  launched using the "A" packet.
+//
+// PRIORITY TO IMPLEMENT
+//  Low. Only needed if the remote target wants to launch a target after
+//  making a connection to a GDB server that isn't already connected to
+//  an inferior process.
 //----------------------------------------------------------------------
 
 Both GDB and LLDB support passing down environment variables. Is it ok to
@@ -79,8 +97,14 @@
 // "QSetSTDOUT:<ascii-hex-path>"
 // "QSetSTDERR:<ascii-hex-path>"
 //
-// Setup where STDIN, STDOUT, and STDERR go prior to sending an "A" 
-// packet
+// BRIEF
+//  Setup where STDIN, STDOUT, and STDERR go prior to sending an "A" 
+//  packet.
+//
+// PRIORITY TO IMPLEMENT
+//  Low. Only needed if the remote target wants to launch a target after
+//  making a connection to a GDB server that isn't already connected to
+//  an inferior process.
 //----------------------------------------------------------------------
 
 When launching a program through the GDB remote protocol with the "A" packet,
@@ -95,7 +119,13 @@
 //----------------------------------------------------------------------
 // "QSetWorkingDir:<ascii-hex-path>"
 //
-// Set the working directory prior to sending an "A" packet.
+// BRIEF
+//  Set the working directory prior to sending an "A" packet.
+//
+// PRIORITY TO IMPLEMENT
+//  Low. Only needed if the remote target wants to launch a target after
+//  making a connection to a GDB server that isn't already connected to
+//  an inferior process.
 //----------------------------------------------------------------------
 
 Or specify the working directory:
@@ -107,7 +137,14 @@
 //----------------------------------------------------------------------
 // "QSetDisableASLR:<bool>"
 //
-/// Enable or disable ASLR on the next "A" packet.
+// BRIEF
+//  Enable or disable ASLR on the next "A" packet.
+//
+// PRIORITY TO IMPLEMENT
+//  Low. Only needed if the remote target wants to launch a target after
+//  making a connection to a GDB server that isn't already connected to
+//  an inferior process and if the target supports disabling ASLR
+//  (Address space layout randomization).
 //----------------------------------------------------------------------
 
 Or control if ASLR is enabled/disabled:
@@ -123,7 +160,14 @@
 //----------------------------------------------------------------------
 // "qRegisterInfo<hex-reg-id>"
 //
-// Discover register information from the remote GDB server.
+// BRIEF
+//  Discover register information from the remote GDB server.
+//
+// PRIORITY TO IMPLEMENT
+//  High. Any target that can self describe its registers, should do so.
+//  This means if new registers are ever added to a remote target, they
+//  will get picked up automatically, and allows registers to change
+//  depending on the actual CPU type that is used.
 //----------------------------------------------------------------------
 
 With LLDB, for register information, remote GDB servers can add support for
@@ -271,65 +315,71 @@
 
 encoding    The encoding type of the register which must be one of: 
 
-		         uint (unsigned integer)
-		         sint (signed integer)
-		         ieee754 (IEEE 754 float)
-		         vector (vector regsiter)
-
-format  	The preferred format for display of this register. The value must
-     		be one of:
-
-				binary
-				decimal
-				hex
-				float
-				vector-sint8
-				vector-uint8 
-				vector-sint16
-				vector-uint16
-				vector-sint32
-				vector-uint32
-				vector-float32
-				vector-uint128
-
-set     	The regiter set name as a string that this register belongs to.
-
-gcc     	The GCC compiler registers number for this register (used for
-     		EH frame and other compiler information that is encoded in the
-     		executable files). 
-
-     		NOTE: If the compiler doesn't have a register number for this 
-     		register, this key/value pair should be omitted.
-
-dwarf  		The DWARF register number for this register that is used for this
-     		register in the debug information. 
-
-     		NOTE: If the compiler doesn't have a register number for this 
-     		register, this key/value pair should be omitted.
-
-generic 	If the register is a generic register that most CPUs have, classify
-     		it correctly so the debugger knows. Valid values are one of:
-	         pc  (a program counter register. for example "name=eip;" (i386), 
-	              "name=rip;" (x86_64), "name=r15;" (32 bit arm) would 
-	              include a "generic=pc;" key value pair)
-	         sp  (a stack pointer register. for example "name=esp;" (i386), 
-	              "name=rsp;" (x86_64), "name=r13;" (32 bit arm) would 
-	              include a "generic=sp;" key value pair)
-	         fp  (a frame pointer register. for example "name=ebp;" (i386), 
-	               "name=rbp;" (x86_64), "name=r7;" (32 bit arm with macosx 
-	               ABI) would include a "generic=fp;" key value pair)
-	         ra  (a return address register. for example "name=lr;" (32 bit ARM) 
-	              would include a "generic=ra;" key value pair)
-	         fp  (a CPU flags register. for example "name=eflags;" (i386), 
-	              "name=rflags;" (x86_64), "name=cpsr;" (32 bit ARM) 
-	              would include a "generic=flags;" key value pair)
-	         arg1 - arg8 (specified for registers that contain function 
-	                  arguments when the argument fits into a register)
+                 uint (unsigned integer)
+                 sint (signed integer)
+                 ieee754 (IEEE 754 float)
+                 vector (vector regsiter)
+
+format      The preferred format for display of this register. The value must
+            be one of:
+
+                binary
+                decimal
+                hex
+                float
+                vector-sint8
+                vector-uint8 
+                vector-sint16
+                vector-uint16
+                vector-sint32
+                vector-uint32
+                vector-float32
+                vector-uint128
+
+set         The regiter set name as a string that this register belongs to.
+
+gcc         The GCC compiler registers number for this register (used for
+            EH frame and other compiler information that is encoded in the
+            executable files). 
+
+            NOTE: If the compiler doesn't have a register number for this 
+            register, this key/value pair should be omitted.
+
+dwarf       The DWARF register number for this register that is used for this
+            register in the debug information. 
+
+            NOTE: If the compiler doesn't have a register number for this 
+            register, this key/value pair should be omitted.
+
+generic     If the register is a generic register that most CPUs have, classify
+            it correctly so the debugger knows. Valid values are one of:
+             pc  (a program counter register. for example "name=eip;" (i386), 
+                  "name=rip;" (x86_64), "name=r15;" (32 bit arm) would 
+                  include a "generic=pc;" key value pair)
+             sp  (a stack pointer register. for example "name=esp;" (i386), 
+                  "name=rsp;" (x86_64), "name=r13;" (32 bit arm) would 
+                  include a "generic=sp;" key value pair)
+             fp  (a frame pointer register. for example "name=ebp;" (i386), 
+                   "name=rbp;" (x86_64), "name=r7;" (32 bit arm with macosx 
+                   ABI) would include a "generic=fp;" key value pair)
+             ra  (a return address register. for example "name=lr;" (32 bit ARM) 
+                  would include a "generic=ra;" key value pair)
+             fp  (a CPU flags register. for example "name=eflags;" (i386), 
+                  "name=rflags;" (x86_64), "name=cpsr;" (32 bit ARM) 
+                  would include a "generic=flags;" key value pair)
+             arg1 - arg8 (specified for registers that contain function 
+                      arguments when the argument fits into a register)
 
 //----------------------------------------------------------------------
 // "qHostInfo"
 //
-// Get information about the host we are remotely connected to.
+// BRIEF
+//  Get information about the host we are remotely connected to.
+//
+// PRIORITY TO IMPLEMENT
+//  High. This packet is usually very easy to implement and can help
+//  LLDB select the correct plug-ins for the job based on the target
+//  triple information that is suppied.
 //----------------------------------------------------------------------
 
 LLDB supports a host info call that gets all sorts of details of the system
@@ -350,8 +400,19 @@
 //----------------------------------------------------------------------
 // "qShlibInfoAddr"
 //
-// Get an address where the dynamic linker stores information about 
-// where shared libraries are loaded.
+// BRIEF
+//  Get an address where the dynamic linker stores information about 
+//  where shared libraries are loaded.
+//
+// PRIORITY TO IMPLEMENT
+//  High if you have a dynamic loader plug-in in LLDB for your target
+//  triple (see the "qHostInfo" packet) that can use this information.
+//  Many times address load randomization can make it hard to detect 
+//  where the dynamic loader binary and data structures are located and
+//  some platforms know, or can find out where this information is.
+//
+//  Low if you have a debug target where all object and symbol files 
+//  contain static load addresses.
 //----------------------------------------------------------------------
 
 LLDB and GDB both support the "qShlibInfoAddr" packet which is a hint to each
@@ -369,9 +430,19 @@
 //----------------------------------------------------------------------
 // "qThreadStopInfo<tid>"
 //
-// Get information about why a thread, whose ID is "<tid>", is stopped.
+// BRIEF
+//  Get information about why a thread, whose ID is "<tid>", is stopped.
+//
+// PRIORITY TO IMPLEMENT
+//  High if you need to support multi-threaded or multi-core debugging.
+//  Many times one thread will hit a breakpoint and while the debugger
+//  is in the process of suspending the other threads, other threads
+//  will also hit a breakpoint. This packet allows LLDB to know why all
+//  threads (live system debug) / cores (JTAG) in your program have 
+//  stopped and allows LLDB to display and control your program 
+//  correctly.
 //----------------------------------------------------------------------
-	
+    
 LLDB tries to use the "qThreadStopInfo" packet which is formatted as
 "qThreadStopInfo%x" where %x is the hex thread ID. This requests information
 about why a thread is stopped. The response is the same as the stop reply
@@ -383,8 +454,18 @@
 //----------------------------------------------------------------------
 // "QThreadSuffixSupported"
 //
-// Try to enable thread suffix support for the 'g', 'G', 'p', and 'P'
-// packets.
+// BRIEF
+//  Try to enable thread suffix support for the 'g', 'G', 'p', and 'P'
+//  packets.
+//
+// PRIORITY TO IMPLEMENT
+//  High. Adding a thread suffix allows us to read and write registers
+//  more efficiently and stops us from having to select a thread with
+//  one packet and then read registers with a second packet. It also
+//  makes sure that no errors can occur where the debugger thinks it
+//  already has a thread selected (see the "Hg" packet from the standard
+//  GDB remote protocol documentation) yet the remote GDB server actually
+//  has another thread selected.
 //----------------------------------------------------------------------
 
 When reading thread registers, you currently need to set the current
@@ -425,8 +506,15 @@
 //----------------------------------------------------------------------
 // "_M<size>,<permissions>"
 //
-// Allocate memory on the remote target with the specified size and
-// permissions.
+// BRIEF
+//  Allocate memory on the remote target with the specified size and
+//  permissions.
+//
+// PRIORITY TO IMPLEMENT
+//  High if you want LLDB to be able to JIT code and run that code. JIT
+//  code also needs data which is also allocated and tracked.
+//
+//  Low if you don't support running JIT'ed code.
 //----------------------------------------------------------------------
 
 The allocate memory packet starts with "_M<size>,<permissions>". It returns a
@@ -436,13 +524,13 @@
 char packet[256];
 int packet_len;
 packet_len = ::snprintf (
-	packet, 
-	sizeof(packet), 
-	"_M%zx,%s%s%s", 
-	(size_t)size,
-	permissions & lldb::ePermissionsReadable ? "r" : "",
-	permissions & lldb::ePermissionsWritable ? "w" : "",
-	permissions & lldb::ePermissionsExecutable ? "x" : "");
+    packet, 
+    sizeof(packet), 
+    "_M%zx,%s%s%s", 
+    (size_t)size,
+    permissions & lldb::ePermissionsReadable ? "r" : "",
+    permissions & lldb::ePermissionsWritable ? "w" : "",
+    permissions & lldb::ePermissionsExecutable ? "x" : "");
 
 You request a size and give the permissions. This packet does NOT need to be
 implemented if you don't want to support running JITed code. The return value
@@ -451,8 +539,15 @@
 //----------------------------------------------------------------------
 // "_m<addr>"
 //
-// Deallocate memory that was previously allocated using an allocate
-// memory pack.
+// BRIEF
+//  Deallocate memory that was previously allocated using an allocate
+//  memory pack.
+//
+// PRIORITY TO IMPLEMENT
+//  High if you want LLDB to be able to JIT code and run that code. JIT
+//  code also needs data which is also allocated and tracked.
+//
+//  Low if you don't support running JIT'ed code.
 //----------------------------------------------------------------------
 
 The deallocate memory packet is "_m<addr>" where you pass in the address you
@@ -463,29 +558,167 @@
 //----------------------------------------------------------------------
 // "qMemoryRegionInfo:<addr>"
 //
-// Get information about the address the range that contains "<addr>"
+// BRIEF
+//  Get information about the address the range that contains "<addr>"
+//
+// PRIORITY TO IMPLEMENT
+//  Medium. This is nice to have, but it isn't necessary. It helps LLDB
+//  do stack unwinding when we branch into memory that isn't executable.
+//  If we can detect that the code we are stopped in isn't executable,
+//  then we can recover registers for stack frames above the current
+//  frame. Otherwise we must assume we are in some JIT'ed code (not JIT
+//  code that LLDB has made) and assume that no registers are available
+//  in higher stack frames.
 //----------------------------------------------------------------------
 
 We added a way to get information for a memory region. The packet is:
 
-	qMemoryRegionInfo:<addr>
-	
+    qMemoryRegionInfo:<addr>
+    
 Where <addr> is a big endian hex address. The response is returned in a series
 of tuples like the data returned in a stop reply packet. The currently valid
 tuples tp return are:
 
-	start:<start-addr>;	// <start-addr> is a big endian hex address that is 
-						// the start address of the range that contains <addr>
-	
-	size:<size>;	// <size> is a big endian hex byte size of the address
-					// of the range that contains <addr>
-	
-	permissions:<permissions>;	// <permissions> is a string that contains one
-								// or more of the characters from "rwx"
-								
-	error:<ascii-byte-error-string>; // where <ascii-byte-error-string> is
-									 // a hex encoded string value that 
-									 // contains an error string
-									
-									
-									
\ No newline at end of file
+    start:<start-addr>; // <start-addr> is a big endian hex address that is 
+                        // the start address of the range that contains <addr>
+    
+    size:<size>;    // <size> is a big endian hex byte size of the address
+                    // of the range that contains <addr>
+    
+    permissions:<permissions>;  // <permissions> is a string that contains one
+                                // or more of the characters from "rwx"
+                                
+    error:<ascii-byte-error-string>; // where <ascii-byte-error-string> is
+                                     // a hex encoded string value that 
+                                     // contains an error string
+                                    
+//----------------------------------------------------------------------
+// Stop reply packet extensions
+//
+// BRIEF
+//  This section describes some of the additional information you can
+//  specify in stop reply packets that help LLDB to know more detailed
+//  information about your threads.
+//
+// DESCRIPTION
+//  Standard GDB remote stop reply packets are reply packets sent in
+//  response to a packet  that made the program run. They come in the
+//  following forms:
+//
+//  "SAA"
+//  "S" means signal and "AA" is a hex signal number that describes why 
+//  the thread or stopped. It doesn't specify which thread, so the "T"
+//  packet is recommended to use instead of the "S" packet.
+//
+//  "TAAkey1:value1;key2:value2;..."
+//  "T" means a thread stopped due to a unix signal where "AA" is a hex 
+//  signal number that describes why the program stopped. This is 
+//  followed by a series of key/value pairs:
+//      - If key is a hex number, it is a register number and value is
+//        the hex value of the register in debuggee endian byte order.
+//      - If key == "thread", then the value is the big endian hex
+//        thread-id of the stopped thread.
+//      - If key == "core", then value is a hex nujber of the core on
+//        which the stop was detected.
+//      - If key == "watch" or key == "rwatch" or key == "awatch", then
+//        value is the data address in big endian hex
+//      - If key == "library", then value is ignore and "qXfer:libraries:read"
+//        packets should be used to detect any newly loaded shared libraries
+//
+//  "WAA"
+//  "W" means the process exited and "AA" is the exit status.
+//
+//  "XAA"
+//  "X" means the process exited and "AA" is signal that caused the program
+//  to exit.
+//
+//  "O<ascii-hex-string>"
+//  "O" means STDOUT has data that was written to its console and is
+//  being delivered to the debugger. This packet happens asynchronously
+//  and the debugger is expected to continue to way for another stop reply
+//  packet.
+//
+// LLDB EXTENSIONS
+//
+//  We have extended the "T" packet to be able to also understand the
+//  following keys and values:
+//
+//  KEY           VALUE     DESCRIPTION
+//  ===========   ========  ================================================
+//  "metype"      unsigned  mach exception type (the value of the EXC_XXX enumerations)
+//                          as an unsigned integer. For targets with mach 
+//                          kernels only.
+//
+//  "mecount"     unsigned  mach exception data count as an unsigned integer
+//                          For targets with mach kernels only.
+//
+//  "medata"      unsigned  There should be "mecount" of these and it is the data
+//                          that goes along with a mach exception (as an unsigned 
+//                          integer). For targets with mach kernels only.
+//
+//  "name"        string    The name of the thread as a plain string. The string
+//                          must not contain an special packet characters or
+//                          contain a ':' or a ';'. Use "hexname" if the thread
+//                          name has special characters.
+//
+//  "hexname"     ascii-hex An ASCII hex string that contains the name of the thread
+//
+//  "qaddr"       hex       Big endian hex value that contains the libdispatch
+//                          queue address for the queue of the thread.
+//
+//  "reason"      enum      The enumeration must be one of:
+//                          "trace" the program stopped after a single instruction
+//                              was executed on a core. Usually done when single
+//                              stepping past a breakpoint
+//                          "breakpoint" a breakpoint set using a 'z' packet was hit.
+//                          "trap" stopped due to user interruption
+//                          "signal" stopped due to an actual unix signal, not
+//                              just the debugger using a unix signal to keep
+//                              the GDB remote client happy.
+//                          "watchpoint". Should be used in conjunction with 
+//                              the "watch"/"rwatch"/"awatch" key value pairs.
+//                          "exception" an exception stop reason. Use with
+//                              the "description" key/value pair to describe the
+//                              exceptional event the user should see as the stop
+//                              reason.
+//  "description" ascii-hex An ASCII hex string that contains a more descriptive
+//                          reason that the thread stopped. This is only needed
+//                          if none of the key/value pairs are enough to
+//                          describe why something stopped.
+//
+// BEST PRACTICES:
+//  Since register values can be supplied with this packet, it is often useful
+//  to return the PC, SP, FP, LR (if any), and FLAGS regsiters so that separate
+//  packets don't need to be sent to read each of these registers from each
+//  thread.
+//
+//  If a thread is stopped for no reason (like just because another thread
+//  stopped, or because when one core stops all cores should stop), use a 
+//  "T" packet with "00" as the signal number and fill in as many key values 
+//  and registers as possible.
+//
+//  LLDB likes to know why a thread stopped since many thread contol 
+//  operations like stepping over a source line, actually are implemented
+//  by running the process multiple times. If a breakpoint is hit while
+//  trying to step over a source line and LLDB finds out that a breakpoint
+//  is hit in the "reason", we will know to stop trying to do the step
+//  over because something happened that should stop us from trying to
+//  do the step. If we are at a breakpoint and we disable the breakpoint
+//  at the current PC and do an instruction single step, knowing that
+//  we stopped due to a "trace" helps us know that we can continue
+//  running versus stopping due to a "breakpoint" (if we have two 
+//  breakpoint instruction on consucutive instructions). So the more info
+//  we can get about the reason a thread stops, the better job LLDB can
+//  do when controlling your process. A typical GDB server behavior is 
+//  to send a SIGTRAP for breakpoints _and_ also when instruction single
+//  stepping, in this case the debugger doesn't really know why we 
+//  stopped and it can make it hard for the debugger to control your
+//  program correctly. What if a real SIGTRAP was delivered to a thread
+//  while we were trying to single step? We woudn't know the difference
+//  with a standard GDB remote server and we could do the wrong thing.
+//
+// PRIORITY TO IMPLEMENT
+//  High. Having the extra information in your stop reply packets makes
+//  your debug session more reliable and informative.
+//----------------------------------------------------------------------
+ 




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