Retro68/binutils/gas/doc/c-or1k.texi

@c Copyright (C) 1991-2022 Free Software Foundation, Inc.
@c This is part of the GAS manual.
@c For copying conditions, see the file as.texinfo.
@ifset GENERIC
@page
@node OpenRISC-Dependent
@chapter OPENRISC Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter OPENRISC Dependent Features
@end ifclear

@cindex OPENRISC support
@menu
* OpenRISC-Syntax::		Syntax
* OpenRISC-Float::		Floating Point
* OpenRISC-Directives::		OpenRISC Machine Directives
* OpenRISC-Opcodes::		Opcodes
@end menu

@cindex OPENRISC syntax
@cindex syntax, OPENRISC
@node OpenRISC-Syntax
@section OpenRISC Syntax
The assembler syntax follows the OpenRISC 1000 Architecture Manual.

@menu
* OpenRISC-Chars::		Special Characters
* OpenRISC-Regs::		Register Names
* OpenRISC-Relocs::		Relocations
@end menu

@node OpenRISC-Chars
@subsection Special Characters

@cindex line comment character, OpenRISC
@cindex OpenRISC line comment character
A @samp{#} character appearing anywhere on a line indicates the start
of a comment that extends to the end of that line.

@cindex line separator, OpenRISC
@cindex statement separator, OpenRISC
@cindex OpenRISC line separator
@samp{;} can be used instead of a newline to separate statements.

@node OpenRISC-Regs
@subsection Register Names
@cindex OpenRISC registers
@cindex register names, OpenRISC

The OpenRISC register file contains 32 general pupose registers.

@itemize @bullet
@item
The 32 general purpose registers are referred to as @samp{r@var{n}}.

@item
The stack pointer register @samp{r1} can be referenced using the alias
@samp{sp}.

@item
The frame pointer register @samp{r2} can be referenced using the alias
@samp{fp}.

@item
The link register @samp{r9} can be referenced using the alias @samp{lr}.
@end itemize

Floating point operations use the same general purpose registers.  The
instructions @code{lf.itof.s} (single precision) and @code{lf.itof.d} (double
precision) can be used to convert integer values to floating point.
Likewise, instructions @code{lf.ftoi.s} (single precision) and
@code{lf.ftoi.d} (double precision) can be used to convert floating point to
integer.

OpenRISC also contains privileged special purpose registers (SPRs).  The
SPRs are accessed using the @code{l.mfspr} and @code{l.mtspr} instructions.

@node OpenRISC-Relocs
@subsection Relocations
@cindex OpenRISC relocations
@cindex relocations, OpenRISC

ELF relocations are available as defined in the OpenRISC architecture
specification.

@code{R_OR1K_HI_16_IN_INSN} is obtained using @samp{hi} and
@code{R_OR1K_LO_16_IN_INSN} and @code{R_OR1K_SLO16} are obtained using
@samp{lo}.  For signed offsets @code{R_OR1K_AHI16} is obtained from
@samp{ha}.  For example:

@example
l.movhi r5, hi(symbol)
l.ori   r5, r5, lo(symbol)

l.movhi r5, ha(symbol)
l.addi  r5, r5, lo(symbol)
@end example

These ``high'' mnemonics extract bits 31:16 of their operand,
and the ``low'' mnemonics extract bits 15:0 of their operand.

The PC relative relocation @code{R_OR1K_GOTPC_HI16} can be obtained by
enclosing an operand inside of @samp{gotpchi}.  Likewise, the
@code{R_OR1K_GOTPC_LO16} relocation can be obtained using @samp{gotpclo}.
These are mostly used when assembling PIC code.  For example, the
standard PIC sequence on OpenRISC to get the base of the global offset
table, PC relative, into a register, can be performed as:

@example
l.jal   0x8
 l.movhi r17, gotpchi(_GLOBAL_OFFSET_TABLE_-4)
l.ori   r17, r17, gotpclo(_GLOBAL_OFFSET_TABLE_+0)
l.add   r17, r17, r9
@end example

Several relocations exist to allow the link editor to perform GOT data
references.  The @code{R_OR1K_GOT16} relocation can obtained by enclosing an
operand inside of @samp{got}.  For example, assuming the GOT base is in
register @code{r17}.

@example
l.lwz   r19, got(a)(r17)
l.lwz   r21, 0(r19)
@end example

Also, several relocations exist for local GOT references.  The
@code{R_OR1K_GOTOFF_AHI16} relocation can obtained by enclosing an operand
inside of @samp{gotoffha}.  Likewise, @code{R_OR1K_GOTOFF_LO16} and
@code{R_OR1K_GOTOFF_SLO16} can be obtained by enclosing an operand inside of
@samp{gotofflo}.  For example, assuming the GOT base is in register
@code{rl7}:

@example
l.movhi r19, gotoffha(symbol)
l.add   r19, r19, r17
l.lwz   r19, gotofflo(symbol)(r19)
@end example

The above PC relative relocations use a @code{l.jal} (jump) instruction
and reading of the link register to load the PC.  OpenRISC also supports
page offset PC relative locations without a jump instruction using the
@code{l.adrp} instruction.  By default the @code{l.adrp} instruction will
create an @code{R_OR1K_PCREL_PG21} relocation.
Likewise, @code{BFD_RELOC_OR1K_LO13} and @code{BFD_RELOC_OR1K_SLO13} can
be obtained by enclosing an operand inside of @samp{po}.  For example:

@example
l.adrp  r3, symbol
l.ori   r4, r3, po(symbol)
l.lbz   r5, po(symbol)(r3)
l.sb    po(symbol)(r3), r6
@end example

Likewise the page offset relocations can be used with GOT references.  The
relocation @code{R_OR1K_GOT_PG21} can be obtained by enclosing an
@code{l.adrp} immediate operand inside of @samp{got}.  Likewise,
@code{R_OR1K_GOT_LO13} can be obtained by enclosing an operand inside of
@samp{gotpo}.  For example to load the value of a GOT symbol into register
@samp{r5} we can do:

@example
l.adrp  r17, got(_GLOBAL_OFFSET_TABLE_)
l.lwz   r5, gotpo(symbol)(r17)
@end example

There are many relocations that can be requested for access to
thread local storage variables.  All of the OpenRISC TLS mnemonics
are supported:

@itemize @bullet
@item
@code{R_OR1K_TLS_GD_HI16} is requested using @samp{tlsgdhi}.
@item
@code{R_OR1K_TLS_GD_LO16} is requested using @samp{tlsgdlo}.
@item
@code{R_OR1K_TLS_GD_PG21} is requested using @samp{tldgd}.
@item
@code{R_OR1K_TLS_GD_LO13} is requested using @samp{tlsgdpo}.

@item
@code{R_OR1K_TLS_LDM_HI16} is requested using @samp{tlsldmhi}.
@item
@code{R_OR1K_TLS_LDM_LO16} is requested using @samp{tlsldmlo}.
@item
@code{R_OR1K_TLS_LDM_PG21} is requested using @samp{tldldm}.
@item
@code{R_OR1K_TLS_LDM_LO13} is requested using @samp{tlsldmpo}.

@item
@code{R_OR1K_TLS_LDO_HI16} is requested using @samp{dtpoffhi}.
@item
@code{R_OR1K_TLS_LDO_LO16} is requested using @samp{dtpofflo}.

@item
@code{R_OR1K_TLS_IE_HI16} is requested using @samp{gottpoffhi}.
@item
@code{R_OR1K_TLS_IE_AHI16} is requested using @samp{gottpoffha}.
@item
@code{R_OR1K_TLS_IE_LO16} is requested using @samp{gottpofflo}.
@item
@code{R_OR1K_TLS_IE_PG21} is requested using @samp{gottp}.
@item
@code{R_OR1K_TLS_IE_LO13} is requested using @samp{gottppo}.

@item
@code{R_OR1K_TLS_LE_HI16} is requested using @samp{tpoffhi}.
@item
@code{R_OR1K_TLS_LE_AHI16} is requested using @samp{tpoffha}.
@item
@code{R_OR1K_TLS_LE_LO16} is requested using @samp{tpofflo}.
@item
@code{R_OR1K_TLS_LE_SLO16} also is requested using @samp{tpofflo}
depending on the instruction format.
@end itemize

Here are some example TLS model sequences.

First, General Dynamic:

@example
l.movhi r17, tlsgdhi(symbol)
l.ori   r17, r17, tlsgdlo(symbol)
l.add   r17, r17, r16
l.or    r3, r17, r17
l.jal   plt(__tls_get_addr)
 l.nop
@end example

Initial Exec:

@example
l.movhi r17, gottpoffhi(symbol)
l.add   r17, r17, r16
l.lwz   r17, gottpofflo(symbol)(r17)
l.add   r17, r17, r10
l.lbs   r17, 0(r17)
@end example

And finally, Local Exec:

@example
l.movhi r17, tpoffha(symbol)
l.add   r17, r17, r10
l.addi  r17, r17, tpofflo(symbol)
l.lbs   r17, 0(r17)
@end example

@node OpenRISC-Float
@section Floating Point

@cindex floating point, OPENRISC (@sc{ieee})
@cindex OPENRISC floating point (@sc{ieee})
OpenRISC uses @sc{ieee} floating-point numbers.

@node OpenRISC-Directives
@section OpenRISC Machine Directives

@cindex OPENRISC machine directives
@cindex machine directives, OPENRISC
The OpenRISC version of @code{@value{AS}} supports the following additional
machine directives:

@table @code
@cindex @code{align} directive, OpenRISC
@item .align
This must be followed by the desired alignment in bytes.

@cindex @code{word} directive, OpenRISC
@item .word
On the OpenRISC, the @code{.word} directive produces a 32 bit value.

@cindex @code{nodelay} directive, OpenRISC
@item .nodelay
On the OpenRISC, the @code{.nodelay} directive sets a flag in elf binaries
indicating that the binary is generated catering for no delay slots.

@cindex @code{proc} directive, OpenRISC
@item .proc
This directive is ignored.  Any text following it on the same
line is also ignored.

@cindex @code{endproc} directive, OpenRISC
@item .endproc
This directive is ignored.  Any text following it on the same
line is also ignored.
@end table

@node OpenRISC-Opcodes
@section Opcodes

@cindex OpenRISC opcode summary
@cindex opcode summary, OpenRISC
@cindex mnemonics, OpenRISC
@cindex instruction summary, LM32
For detailed information on the OpenRISC machine instruction set, see
@url{http://www.openrisc.io/architecture/}.

@code{@value{AS}} implements all the standard OpenRISC opcodes.