Ubuntu Manpage: libunwind-ia64 -- IA-64-specific support in libunwind

Provided by: libunwind-dev_1.6.2-3_amd64

NAME

       libunwind-ia64 -- IA-64-specific support in libunwind

INTRODUCTION

       The  IA-64  version  of  libunwind uses a platform-string of ia64 and, at least in theory,
       should be able to support all operating systems adhering  to  the  processor-specific  ABI
       defined  for  the  Itanium  Processor  Family.  This includes both little-endian Linux and
       big-endian HP-UX. Furthermore, to make it possible for a single library to unwind both 32-
       and  64-bit targets, the type unw_word_t is always defined to be 64 bits wide (independent
       of the natural word-size of the host). Having said that, the  current  implementation  has
       been tested only with IA-64 Linux.

       When targeting IA-64, the libunwind header file defines the macro UNW_TARGET_IA64 as 1 and
       the macro UNW_TARGET as ``ia64'' (without  the  quotation  marks).  The  former  makes  it
       possible  for  platform-dependent  unwind code to use conditional-compilation to select an
       appropriate implementation. The latter is  useful  for  stringification  purposes  and  to
       construct target-platform-specific symbols.

       One  special  feature  of  IA-64  is the use of NaT bits to support speculative execution.
       Often, NaT bits are thought of as the ``65-th bit'' of a  general  register.  However,  to
       make everything fit into 64-bit wide unw_word_t values, libunwind treats the NaT-bits like
       separate boolean registers, whose 64-bit value is either TRUE (non-zero) or FALSE (zero).

MACHINE-STATE

       The machine-state (set of registers) that is accessible through libunwind depends  on  the
       type  of  stack  frame  that  a  cursor  points  to.  For normal frames, all ``preserved''
       (callee-saved) registers are  accessible.  For  signal-trampoline  frames,  all  registers
       (including  ``scratch'' (caller-saved) registers) are accessible. Most applications do not
       have to worry a-priori about which registers are accessible when. In case of doubt, it  is
       always  safe to try to access a register (via unw_get_reg() or unw_get_fpreg()) and if the
       register isn't accessible, the call will fail with a return-value of -UNW_EBADREG.

       As a special exception to the above general rule, scratch  registers  r15-r18  are  always
       accessible,  even  in  normal  frames.  This makes it possible to pass arguments, e.g., to
       exception handlers.

       For a detailed description  of  the  IA-64  register  usage  convention,  please  see  the
       ``Itanium Software Conventions and Runtime Architecture Guide'', available at:
                        http://www.intel.com/design/itanium/downloads/245358.htm

REGISTER NAMES

The IA-64-version of libunwind defines three kinds of register name macros: frame-register
macros, normal register macros, and convenience macros. Below, we describe each kind in
turn:

FRAME-REGISTER MACROS
Frame-registers are special (pseudo) registers because they always have a valid value,
even though sometimes they do not get saved explicitly (e.g., if a memory stack frame is
16 bytes in size, the previous stack-pointer value can be calculated simply as sp+16, so
there is no need to save the stack-pointer explicitly). Moreover, the set of frame
register values uniquely identifies a stack frame. The IA-64 architecture defines two
stacks (a memory and a register stack). Including the instruction-pointer (IP), this means
there are three frame registers:

UNW_IA64_IP:
Contains the instruction pointer (IP, or ``program counter'') of the current stack
frame. Given this value, the remaining machine-state corresponds to the
register-values that were present in the CPU when it was just about to execute the
instruction pointed to by UNW_IA64_IP. Bits 0 and 1 of this frame-register encode
the slot number of the instruction. Note: Due to the way the call instruction
works on IA-64, the slot number is usually zero, but can be non-zero, e.g., in the
stack-frame of a signal-handler trampoline.

UNW_IA64_SP:
Contains the (memory) stack-pointer value (SP).

UNW_IA64_BSP:
Contains the register backing-store pointer (BSP). Note: the value in this
register is equal to the contents of register ar.bsp at the time the instruction at
UNW_IA64_IP was about to begin execution.

NORMAL REGISTER MACROS
The following normal register name macros are available:

UNW_IA64_GR:
The base-index for general (integer) registers. Add an index in the range from
0..127 to get a particular general register. For example, to access r4, the index
UNW_IA64_GR+4 should be used. Registers r0 and r1 (gp) are read-only, and any
attempt to write them will result in an error (-UNW_EREADONLYREG). Even though r1
is read-only, libunwind will automatically adjust its value if the
instruction-pointer (UNW_IA64_IP) is modified. For example, if UNW_IA64_IP is set
to a value inside a function func(), then reading UNW_IA64_GR+1 will return the
global-pointer value for this function.

UNW_IA64_NAT:
The base-index for the NaT bits of the general (integer) registers. A non-zero
value in these registers corresponds to a set NaT-bit. Add an index in the range
from 0..127 to get a particular NaT-bit register. For example, to access the NaT
bit of r4, the index UNW_IA64_NAT+4 should be used.

UNW_IA64_FR:
The base-index for floating-point registers. Add an index in the range from 0..127
to get a particular floating-point register. For example, to access f2, the index
UNW_IA64_FR+2 should be used. Registers f0 and f1 are read-only, and any attempt to
write to indices UNW_IA64_FR+0 or UNW_IA64_FR+1 will result in an error
(-UNW_EREADONLYREG).

UNW_IA64_AR:
The base-index for application registers. Add an index in the range from 0..127 to
get a particular application register. For example, to access ar40, the index
UNW_IA64_AR+40 should be used. The IA-64 architecture defines several application
registers as ``reserved for future use''. Attempting to access such registers
results in an error (-UNW_EBADREG).

UNW_IA64_BR:
The base-index for branch registers. Add an index in the range from 0..7 to get a
particular branch register. For example, to access b6, the index UNW_IA64_BR+6
should be used.

UNW_IA64_PR:
Contains the set of predicate registers. This 64-bit wide register contains
registers p0 through p63 in the ``broad-side'' format. Just like with the ``move
predicates'' instruction, the registers are mapped as if CFM.rrb.pr were set to 0.
Thus, in general the value of predicate register pN with N>=16 can be found in bit
16 + ((N-16)+CFM.rrb.pr) % 48.

UNW_IA64_CFM:
Contains the current-frame-mask register.

CONVENIENCE MACROS
Convenience macros are simply aliases for certain frequently used registers:

UNW_IA64_GP:
Alias for UNW_IA64_GR+1, the global-pointer register.

UNW_IA64_TP:
Alias for UNW_IA64_GR+13, the thread-pointer register.

UNW_IA64_AR_RSC:
Alias for UNW_IA64_GR+16, the register-stack configuration register.

UNW_IA64_AR_BSP:
Alias for UNW_IA64_GR+17. This register index accesses the value of register
ar.bsp as of the time it was last saved explicitly. This is rarely what you want.
Normally, you'll want to use UNW_IA64_BSP instead.

UNW_IA64_AR_BSPSTORE:
Alias for UNW_IA64_GR+18, the register-backing store write pointer.

UNW_IA64_AR_RNAT:
Alias for UNW_IA64_GR+19, the register-backing store NaT-collection register.

UNW_IA64_AR_CCV:
Alias for UNW_IA64_GR+32, the compare-and-swap value register.

UNW_IA64_AR_CSD:
Alias for UNW_IA64_GR+25, the compare-and-swap-data register (used by 16-byte
atomic operations).

UNW_IA64_AR_UNAT:
Alias for UNW_IA64_GR+36, the user NaT-collection register.

UNW_IA64_AR_FPSR:
Alias for UNW_IA64_GR+40, the floating-point status (and control) register.

UNW_IA64_AR_PFS:
Alias for UNW_IA64_GR+64, the previous frame-state register.

UNW_IA64_AR_LC:
Alias for UNW_IA64_GR+65 the loop-count register.

UNW_IA64_AR_EC:
Alias for UNW_IA64_GR+66, the epilogue-count register.

THE UNWIND-CONTEXT TYPE

       On IA-64, unw_context_t is simply an alias for ucontext_t (as defined by the  Single  UNIX
       Spec).  This  implies that it is possible to initialize a value of this type not just with
       unw_getcontext(), but also with getcontext(), for  example.  However,  since  this  is  an
       IA-64-specific extension to libunwind, portable code should not rely on this equivalence.

AUTHOR