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.\" Manual page created with latex2man on Fri Jan 17 15:46:04 PST 2003
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.TH "LIBUNWIND\-IA64" "3" "17 January 2003" "Programming Library " "Programming Library "
.SH NAME
libunwind\-ia64 \-\- IA\-64\-specific support in libunwind
.PP
.SH INTRODUCTION
.PP
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.
.PP
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.
.PP
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).
.PP
.SH MACHINE\-STATE
.PP
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 \fItry\fP
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\&.
.PP
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.
.PP
For a detailed description of the IA\-64 register usage convention,
please see the ``Itanium Software Conventions and Runtime Architecture
Guide\&'', available at:
.ce 100
\fBhttp://www.intel.com/design/itanium/downloads/245358.htm\fP
.ce 0
.PP
.SH REGISTER NAMES
.PP
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:
.PP
.SS FRAME\-REGISTER MACROS
.PP
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:
.TP
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.
\fBNote:\fP
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.
.TP
UNW_IA64_SP:
Contains the (memory) stack\-pointer
value (SP). This frame\-register is read\-only.
.TP
UNW_IA64_BSP:
Contains the register backing\-store
pointer (BSP). This frame\-register is read\-only. \fBNote:\fP
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.
.PP
.SS NORMAL REGISTER MACROS
.PP
The following normal register name macros are available:
.TP
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. Register
r0
is read\-only, and any attempt to write to index
UNW_IA64_GR+0
will result in an error
(\-UNW_EREADONLYREG).
.TP
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.
.TP
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).
.TP
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).
.TP
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.
.TP
UNW_IA64_PR:
Contains the set of predicate registers.
This 64\-bit wide register contains registers p0
through
p63
in the ``broad\-side\&'' format (i.e., p0
corresponds to bit 0, p1
to bit 1, and so on).
.TP
UNW_IA64_CFM:
Contains the current\-frame\-mask
register.
.PP
.SS CONVENIENCE MACROS
.PP
Convenience macros are simply aliases for certain frequently used
registers:
.TP
UNW_IA64_GP:
Alias for UNW_IA64_GR+1\&.
The global\-pointer register. For unwinding\-purposes, this register
is treated as read\-only.
.TP
UNW_IA64_TP:
Alias for UNW_IA64_GR+13\&.
The thread\-pointer register. For unwinding\-purposes, this register is
treated as read\-only.
.TP
UNW_IA64_AR_RSC:
Alias for UNW_IA64_GR+16\&.
The register\-stack configuration register.
.TP
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.
.TP
UNW_IA64_AR_BSPSTORE:
Alias for UNW_IA64_GR+18\&.
The register\-backing store write pointer.
.TP
UNW_IA64_AR_RNAT:
Alias for UNW_IA64_GR+19\&.
The register\-backing store NaT\-collection register.
.TP
UNW_IA64_AR_CCV:
Alias for UNW_IA64_GR+32\&.
The compare\-and\-swap value register.
.TP
UNW_IA64_AR_UNAT:
Alias for UNW_IA64_GR+36\&.
The user NaT\-collection register.
.TP
UNW_IA64_AR_FPSR:
Alias for UNW_IA64_GR+40\&.
The floating\-point status (and control) register.
.TP
UNW_IA64_AR_PFS:
Alias for UNW_IA64_GR+64\&.
The previous frame\-state register.
.TP
UNW_IA64_AR_LC:
Alias for UNW_IA64_GR+65\&.
The loop\-count register.
.TP
UNW_IA64_AR_EC:
Alias for UNW_IA64_GR+66\&.
The epilogue\-count register.
.PP
.SH THE UNWIND\-CONTEXT TYPE
.PP
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.
.PP
.SH SEE ALSO
.PP
libunwind(3)
.PP
.SH AUTHOR
.PP
David Mosberger\-Tang
.br
Hewlett\-Packard Labs
.br
Palo\-Alto, CA 94304
.br
Email: \fBdavidm@hpl.hp.com\fP
.br
WWW: \fBhttp://www.hpl.hp.com/research/linux/libunwind/\fP\&.
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\documentclass{article}
\usepackage[fancyhdr,pdf]{latex2man}
\input{common.tex}
\begin{document}
\begin{Name}{3}{libunwind-ia64}{David Mosberger-Tang}{Programming Library}{IA-64-specific support in libunwind}
libunwind-ia64 -- IA-64-specific support in libunwind
\end{Name}
\section{Introduction}
The IA-64 version of \Prog{libunwind} uses a platform-string of
\texttt{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
\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 \Prog{libunwind} header file defines the
macro \Const{UNW\_TARGET\_IA64} as 1 and the macro \Const{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 \Type{unw\_word\_t} values, \Prog{libunwind} treats the
NaT-bits like separate boolean registers, whose 64-bit value is either
TRUE (non-zero) or FALSE (zero).
\section{Machine-State}
The machine-state (set of registers) that is accessible through
\Prog{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 \emph{try} to
access a register (via \Func{unw\_get\_reg}() or
\Func{unw\_get\_fpreg}()) and if the register isn't accessible, the
call will fail with a return-value of \texttt{-}\Const{UNW\_EBADREG}.
As a special exception to the above general rule, scratch registers
\texttt{r15}-\texttt{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:
\begin{center}
\URL{http://www.intel.com/design/itanium/downloads/245358.htm}
\end{center}
\section{Register Names}
The IA-64-version of \Prog{libunwind} defines three kinds of register
name macros: frame-register macros, normal register macros, and
convenience macros. Below, we describe each kind in turn:
\subsection{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
\texttt{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:
\begin{Description}
\item[\Const{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 \Const{UNW\_IA64\_IP}. Bits 0 and 1 of
this frame-register encode the slot number of the instruction.
\textbf{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.
\item[\Const{UNW\_IA64\_SP}:] Contains the (memory) stack-pointer
value (SP). This frame-register is read-only.
\item[\Const{UNW\_IA64\_BSP}:] Contains the register backing-store
pointer (BSP). This frame-register is read-only. \textbf{Note:}
the value in this register is equal to the contents of register
\texttt{ar.bsp} at the time the instruction at \Const{UNW\_IA64\_IP}
was about to begin execution.
\end{Description}
\subsection{Normal Register Macros}
The following normal register name macros are available:
\begin{Description}
\item[\Const{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 \texttt{r4},
the index \Const{UNW\_IA64\_GR}\texttt{+4} should be used. Register
\texttt{r0} is read-only, and any attempt to write to index
\Const{UNW\_IA64\_GR}\texttt{+0} will result in an error
(\texttt{-}\Const{UNW\_EREADONLYREG}).
\item[\Const{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 \texttt{r4}, the index \Const{UNW\_IA64\_NAT}\texttt{+4}
should be used.
\item[\Const{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
\texttt{f2}, the index \Const{UNW\_IA64\_FR}\texttt{+2} should be
used. Registers \texttt{f0} and \texttt{f1} are read-only, and any
attempt to write to indices \Const{UNW\_IA64\_FR}\texttt{+0} or
\Const{UNW\_IA64\_FR}\texttt{+1} will result in an error
(\texttt{-}\Const{UNW\_EREADONLYREG}).
\item[\Const{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
\texttt{ar40}, the index \Const{UNW\_IA64\_AR}\texttt{+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 (\texttt{-}\Const{UNW\_EBADREG}).
\item[\Const{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 \texttt{b6}, the index
\Const{UNW\_IA64\_BR}\texttt{+6} should be used.
\item[\Const{UNW\_IA64\_PR}:] Contains the set of predicate registers.
This 64-bit wide register contains registers \texttt{p0} through
\texttt{p63} in the ``broad-side'' format (i.e., \texttt{p0}
corresponds to bit 0, \texttt{p1} to bit 1, and so on).
\item[\Const{UNW\_IA64\_CFM}:] Contains the current-frame-mask
register.
\end{Description}
\subsection{Convenience Macros}
Convenience macros are simply aliases for certain frequently used
registers:
\begin{Description}
\item[\Const{UNW\_IA64\_GP}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+1}.
The global-pointer register. For unwinding-purposes, this register
is treated as read-only.
\item[\Const{UNW\_IA64\_TP}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+13}.
The thread-pointer register. For unwinding-purposes, this register is
treated as read-only.
\item[\Const{UNW\_IA64\_AR\_RSC}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+16}.
The register-stack configuration register.
\item[\Const{UNW\_IA64\_AR\_BSP}:] Alias for
\Const{UNW\_IA64\_GR}\texttt{+17}. This register index accesses the
value of register \texttt{ar.bsp} as of the time it was last saved
explicitly. This is rarely what you want. Normally, you'll want to
use \Const{UNW\_IA64\_BSP} instead.
\item[\Const{UNW\_IA64\_AR\_BSPSTORE}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+18}.
The register-backing store write pointer.
\item[\Const{UNW\_IA64\_AR\_RNAT}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+19}.
The register-backing store NaT-collection register.
\item[\Const{UNW\_IA64\_AR\_CCV}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+32}.
The compare-and-swap value register.
\item[\Const{UNW\_IA64\_AR\_UNAT}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+36}.
The user NaT-collection register.
\item[\Const{UNW\_IA64\_AR\_FPSR}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+40}.
The floating-point status (and control) register.
\item[\Const{UNW\_IA64\_AR\_PFS}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+64}.
The previous frame-state register.
\item[\Const{UNW\_IA64\_AR\_LC}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+65}.
The loop-count register.
\item[\Const{UNW\_IA64\_AR\_EC}:] Alias for \Const{UNW\_IA64\_GR}\texttt{+66}.
The epilogue-count register.
\end{Description}
\section{The Unwind-Context Type}
On IA-64, \Type{unw\_context\_t} is simply an alias for
\Type{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
\Func{unw\_getcontext}(), but also with \Func{getcontext}(), for
example. However, since this is an IA-64-specific extension to
\Prog{libunwind}, portable code should not rely on this equivalence.
\section{See Also}
\SeeAlso{libunwind(3)}
\section{Author}
\noindent
David Mosberger-Tang\\
Hewlett-Packard Labs\\
Palo-Alto, CA 94304\\
Email: \Email{davidm@hpl.hp.com}\\
WWW: \URL{http://www.hpl.hp.com/research/linux/libunwind/}.
\LatexManEnd
\end{document}