import gdb-1999-06-28 snapshot

[deliverable/binutils-gdb.git] / gdb / config / convex / Convex.notes

@c OBSOLETE 
@c OBSOLETE @node Convex,,, Top
@c OBSOLETE @appendix Convex-specific info
@c OBSOLETE @cindex Convex notes
@c OBSOLETE 
@c OBSOLETE Scalar registers are 64 bits long, which is a pain since
@c OBSOLETE left half of an S register frequently contains noise.
@c OBSOLETE Therefore there are two ways to obtain the value of an S register.
@c OBSOLETE 
@c OBSOLETE @table @kbd
@c OBSOLETE @item $s0
@c OBSOLETE returns the low half of the register as an int
@c OBSOLETE 
@c OBSOLETE @item $S0
@c OBSOLETE returns the whole register as a long long
@c OBSOLETE @end table
@c OBSOLETE 
@c OBSOLETE You can print the value in floating point by using @samp{p/f $s0} or @samp{p/f $S0}
@c OBSOLETE to print a single or double precision value.
@c OBSOLETE 
@c OBSOLETE @cindex vector registers
@c OBSOLETE Vector registers are handled similarly, with @samp{$V0} denoting the whole
@c OBSOLETE 64-bit register and @kbd{$v0} denoting the 32-bit low half; @samp{p/f $v0}
@c OBSOLETE or @samp{p/f $V0} can be used to examine the register in floating point.
@c OBSOLETE The length of the vector registers is taken from @samp{$vl}.  
@c OBSOLETE 
@c OBSOLETE Individual elements of a vector register are denoted in the obvious way;
@c OBSOLETE @samp{print $v3[9]} prints the tenth element of register @kbd{v3}, and
@c OBSOLETE @samp{set $v3[9] = 1234} alters it.
@c OBSOLETE 
@c OBSOLETE @kbd{$vl} and @kbd{$vs} are int, and @kbd{$vm} is an int vector.
@c OBSOLETE Elements of @kbd{$vm} can't be assigned to.
@c OBSOLETE 
@c OBSOLETE @cindex communication registers
@c OBSOLETE @kindex info comm-registers
@c OBSOLETE Communication registers have names @kbd{$C0 .. $C63}, with @kbd{$c0 .. $c63}
@c OBSOLETE denoting the low-order halves.  @samp{info comm-registers} will print them
@c OBSOLETE all out, and tell which are locked.  (A communication register is
@c OBSOLETE locked when a value is sent to it, and unlocked when the value is
@c OBSOLETE received.)  Communication registers are, of course, global to all
@c OBSOLETE threads, so it does not matter what the currently selected thread is.
@c OBSOLETE @samp{info comm-reg @var{name}} prints just that one communication
@c OBSOLETE register; @samp{name} may also be a communication register number
@c OBSOLETE @samp{nn} or @samp{0xnn}.
@c OBSOLETE @samp{info comm-reg @var{address}} prints the contents of the resource
@c OBSOLETE structure at that address.
@c OBSOLETE 
@c OBSOLETE @kindex info psw
@c OBSOLETE The command @samp{info psw} prints the processor status word @kbd{$ps}
@c OBSOLETE bit by bit.
@c OBSOLETE 
@c OBSOLETE @kindex set base
@c OBSOLETE GDB normally prints all integers in base 10, but the leading
@c OBSOLETE @kbd{0x80000000} of pointers is intolerable in decimal, so the default
@c OBSOLETE output radix has been changed to try to print addresses appropriately.
@c OBSOLETE The @samp{set base} command can be used to change this.
@c OBSOLETE 
@c OBSOLETE @table @code
@c OBSOLETE @item set base 10
@c OBSOLETE Integer values always print in decimal.
@c OBSOLETE 
@c OBSOLETE @item set base 16
@c OBSOLETE Integer values always print in hex.
@c OBSOLETE 
@c OBSOLETE @item set base
@c OBSOLETE Go back to the initial state, which prints integer values in hex if they
@c OBSOLETE look like pointers (specifically, if they start with 0x8 or 0xf in the
@c OBSOLETE stack), otherwise in decimal.
@c OBSOLETE @end table
@c OBSOLETE 
@c OBSOLETE @kindex set pipeline
@c OBSOLETE When an exception such as a bus error or overflow happens, usually the PC
@c OBSOLETE is several instructions ahead by the time the exception is detected.
@c OBSOLETE The @samp{set pipe} command will disable this.
@c OBSOLETE 
@c OBSOLETE @table @code
@c OBSOLETE @item set pipeline off
@c OBSOLETE Forces serial execution of instructions; no vector chaining and no 
@c OBSOLETE scalar instruction overlap.  With this, exceptions are detected with 
@c OBSOLETE the PC pointing to the instruction after the one in error.
@c OBSOLETE 
@c OBSOLETE @item set pipeline on
@c OBSOLETE Returns to normal, fast, execution.  This is the default.
@c OBSOLETE @end table
@c OBSOLETE 
@c OBSOLETE @cindex parallel
@c OBSOLETE In a parallel program, multiple threads may be executing, each
@c OBSOLETE with its own registers, stack, and local memory.  When one of them
@c OBSOLETE hits a breakpoint, that thread is selected.  Other threads do
@c OBSOLETE not run while the thread is in the breakpoint.
@c OBSOLETE 
@c OBSOLETE @kindex 1cont
@c OBSOLETE The selected thread can be single-stepped, given signals, and so
@c OBSOLETE on.  Any other threads remain stopped.  When a @samp{cont} command is given,
@c OBSOLETE all threads are resumed.  To resume just the selected thread, use
@c OBSOLETE the command @samp{1cont}.
@c OBSOLETE 
@c OBSOLETE @kindex thread
@c OBSOLETE The @samp{thread} command will show the active threads and the
@c OBSOLETE instruction they are about to execute.  The selected thread is marked
@c OBSOLETE with an asterisk.  The command @samp{thread @var{n}} will select thread @var{n},
@c OBSOLETE shifting the debugger's attention to it for single-stepping,
@c OBSOLETE registers, local memory, and so on.
@c OBSOLETE 
@c OBSOLETE @kindex info threads
@c OBSOLETE The @samp{info threads} command will show what threads, if any, have
@c OBSOLETE invisibly hit breakpoints or signals and are waiting to be noticed.
@c OBSOLETE 
@c OBSOLETE @kindex set parallel
@c OBSOLETE The @samp{set parallel} command controls how many threads can be active.
@c OBSOLETE 
@c OBSOLETE @table @code
@c OBSOLETE @item set parallel off
@c OBSOLETE One thread.  Requests by the program that other threads join in
@c OBSOLETE (spawn and pfork instructions) do not cause other threads to start up.
@c OBSOLETE This does the same thing as the @samp{limit concurrency 1} command.
@c OBSOLETE 
@c OBSOLETE @item set parallel fixed
@c OBSOLETE All CPUs are assigned to your program whenever it runs.  When it
@c OBSOLETE executes a pfork or spawn instruction, it begins parallel execution
@c OBSOLETE immediately.  This does the same thing as the @samp{mpa -f} command.
@c OBSOLETE 
@c OBSOLETE @item set parallel on
@c OBSOLETE One or more threads.  Spawn and pfork cause CPUs to join in when and if
@c OBSOLETE they are free.  This is the default.  It is very good for system
@c OBSOLETE throughput, but not very good for finding bugs in parallel code.  If you
@c OBSOLETE suspect a bug in parallel code, you probably want @samp{set parallel fixed.}
@c OBSOLETE @end table
@c OBSOLETE 
@c OBSOLETE @subsection Limitations
@c OBSOLETE 
@c OBSOLETE WARNING: Convex GDB evaluates expressions in long long, because S
@c OBSOLETE registers are 64 bits long.  However, GDB expression semantics are not
@c OBSOLETE exactly C semantics.  This is a bug, strictly speaking, but it's not one I
@c OBSOLETE know how to fix.  If @samp{x} is a program variable of type int, then it
@c OBSOLETE is also type int to GDB, but @samp{x + 1} is long long, as is @samp{x + y}
@c OBSOLETE or any other expression requiring computation.  So is the expression
@c OBSOLETE @samp{1}, or any other constant.  You only really have to watch out for
@c OBSOLETE calls.  The innocuous expression @samp{list_node (0x80001234)} has an
@c OBSOLETE argument of type long long.  You must explicitly cast it to int.
@c OBSOLETE 
@c OBSOLETE It is not possible to continue after an uncaught fatal signal by using
@c OBSOLETE @samp{signal 0}, @samp{return}, @samp{jump}, or anything else.  The difficulty is with
@c OBSOLETE Unix, not GDB.
@c OBSOLETE 
@c OBSOLETE I have made no big effort to make such things as single-stepping a
@c OBSOLETE @kbd{join} instruction do something reasonable.  If the program seems to
@c OBSOLETE hang when doing this, type @kbd{ctrl-c} and @samp{cont}, or use
@c OBSOLETE @samp{thread} to shift to a live thread.  Single-stepping a @kbd{spawn}
@c OBSOLETE instruction apparently causes new threads to be born with their T bit set;
@c OBSOLETE this is not handled gracefully.  When a thread has hit a breakpoint, other
@c OBSOLETE threads may have invisibly hit the breakpoint in the background; if you
@c OBSOLETE clear the breakpoint gdb will be surprised when threads seem to continue
@c OBSOLETE to stop at it.  All of these situations produce spurious signal 5 traps;
@c OBSOLETE if this happens, just type @samp{cont}.  If it becomes a nuisance, use
@c OBSOLETE @samp{handle 5 nostop}.  (It will ask if you are sure.  You are.)
@c OBSOLETE 
@c OBSOLETE There is no way in GDB to store a float in a register, as with
@c OBSOLETE @kbd{set $s0 = 3.1416}.  The identifier @kbd{$s0} denotes an integer,
@c OBSOLETE and like any C expression which assigns to an integer variable, the
@c OBSOLETE right-hand side is casted to type int.  If you should need to do
@c OBSOLETE something like this, you can assign the value to @kbd{@{float@} ($sp-4)}
@c OBSOLETE and then do @kbd{set $s0 = $sp[-4]}.  Same deal with @kbd{set $v0[69] = 6.9}.