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diff --git a/doc/supplements/sparc/callconv.t b/doc/supplements/sparc/callconv.t deleted file mode 100644 index 590707386b..0000000000 --- a/doc/supplements/sparc/callconv.t +++ /dev/null @@ -1,392 +0,0 @@ -@c -@c COPYRIGHT (c) 1988-1999. -@c On-Line Applications Research Corporation (OAR). -@c All rights reserved. -@c -@c $Id$ -@c - -@chapter Calling Conventions - -@section Introduction - -Each high-level language compiler generates -subroutine entry and exit code based upon a set of rules known -as the compiler's calling convention. These rules address the -following issues: - -@itemize @bullet -@item register preservation and usage - -@item parameter passing - -@item call and return mechanism -@end itemize - -A compiler's calling convention is of importance when -interfacing to subroutines written in another language either -assembly or high-level. Even when the high-level language and -target processor are the same, different compilers may use -different calling conventions. As a result, calling conventions -are both processor and compiler dependent. - -@section Programming Model - -This section discusses the programming model for the -SPARC architecture. - -@subsection Non-Floating Point Registers - -The SPARC architecture defines thirty-two -non-floating point registers directly visible to the programmer. -These are divided into four sets: - -@itemize @bullet -@item input registers - -@item local registers - -@item output registers - -@item global registers -@end itemize - -Each register is referred to by either two or three -names in the SPARC reference manuals. First, the registers are -referred to as r0 through r31 or with the alternate notation -r[0] through r[31]. Second, each register is a member of one of -the four sets listed above. Finally, some registers have an -architecturally defined role in the programming model which -provides an alternate name. The following table describes the -mapping between the 32 registers and the register sets: - -@ifset use-ascii -@example -@group - +-----------------+----------------+------------------+ - | Register Number | Register Names | Description | - +-----------------+----------------+------------------+ - | 0 - 7 | g0 - g7 | Global Registers | - +-----------------+----------------+------------------+ - | 8 - 15 | o0 - o7 | Output Registers | - +-----------------+----------------+------------------+ - | 16 - 23 | l0 - l7 | Local Registers | - +-----------------+----------------+------------------+ - | 24 - 31 | i0 - i7 | Input Registers | - +-----------------+----------------+------------------+ -@end group -@end example -@end ifset - -@ifset use-tex -@sp 1 -@tex -\centerline{\vbox{\offinterlineskip\halign{ -\vrule\strut#& -\hbox to 1.75in{\enskip\hfil#\hfil}& -\vrule#& -\hbox to 1.75in{\enskip\hfil#\hfil}& -\vrule#& -\hbox to 1.75in{\enskip\hfil#\hfil}& -\vrule#\cr -\noalign{\hrule} -&\bf Register Number &&\bf Register Names&&\bf Description&\cr\noalign{\hrule} -&0 - 7&&g0 - g7&&Global Registers&\cr\noalign{\hrule} -&8 - 15&&o0 - o7&&Output Registers&\cr\noalign{\hrule} -&16 - 23&&l0 - l7&&Local Registers&\cr\noalign{\hrule} -&24 - 31&&i0 - i7&&Input Registers&\cr\noalign{\hrule} -}}\hfil} -@end tex -@end ifset - -@ifset use-html -@html -<CENTER> - <TABLE COLS=3 WIDTH="80%" BORDER=2> -<TR><TD ALIGN=center><STRONG>Register Number</STRONG></TD> - <TD ALIGN=center><STRONG>Register Names</STRONG></TD> - <TD ALIGN=center><STRONG>Description</STRONG></TD> -<TR><TD ALIGN=center>0 - 7</TD> - <TD ALIGN=center>g0 - g7</TD> - <TD ALIGN=center>Global Registers</TD></TR> -<TR><TD ALIGN=center>8 - 15</TD> - <TD ALIGN=center>o0 - o7</TD> - <TD ALIGN=center>Output Registers</TD></TR> -<TR><TD ALIGN=center>16 - 23</TD> - <TD ALIGN=center>l0 - l7</TD> - <TD ALIGN=center>Local Registers</TD></TR> -<TR><TD ALIGN=center>24 - 31</TD> - <TD ALIGN=center>i0 - i7</TD> - <TD ALIGN=center>Input Registers</TD></TR> - </TABLE> -</CENTER> -@end html -@end ifset - -As mentioned above, some of the registers serve -defined roles in the programming model. The following table -describes the role of each of these registers: - -@ifset use-ascii -@example -@group - +---------------+----------------+----------------------+ - | Register Name | Alternate Name | Description | - +---------------+----------------+----------------------+ - | g0 | na | reads return 0 | - | | | writes are ignored | - +---------------+----------------+----------------------+ - | o6 | sp | stack pointer | - +---------------+----------------+----------------------+ - | i6 | fp | frame pointer | - +---------------+----------------+----------------------+ - | i7 | na | return address | - +---------------+----------------+----------------------+ -@end group -@end example -@end ifset - -@ifset use-tex -@sp 1 -@tex -\centerline{\vbox{\offinterlineskip\halign{ -\vrule\strut#& -\hbox to 1.75in{\enskip\hfil#\hfil}& -\vrule#& -\hbox to 1.75in{\enskip\hfil#\hfil}& -\vrule#& -\hbox to 1.75in{\enskip\hfil#\hfil}& -\vrule#\cr -\noalign{\hrule} -&\bf Register Name &&\bf Alternate Names&&\bf Description&\cr\noalign{\hrule} -&g0&&NA&&reads return 0; &\cr -&&&&&writes are ignored&\cr\noalign{\hrule} -&o6&&sp&&stack pointer&\cr\noalign{\hrule} -&i6&&fp&&frame pointer&\cr\noalign{\hrule} -&i7&&NA&&return address&\cr\noalign{\hrule} -}}\hfil} -@end tex -@end ifset - -@ifset use-html -@html -<CENTER> - <TABLE COLS=3 WIDTH="80%" BORDER=2> -<TR><TD ALIGN=center><STRONG>Register Name</STRONG></TD> - <TD ALIGN=center><STRONG>Alternate Name</STRONG></TD> - <TD ALIGN=center><STRONG>Description</STRONG></TD></TR> -<TR><TD ALIGN=center>g0</TD> - <TD ALIGN=center>NA</TD> - <TD ALIGN=center>reads return 0 ; writes are ignored</TD></TR> -<TR><TD ALIGN=center>o6</TD> - <TD ALIGN=center>sp</TD> - <TD ALIGN=center>stack pointer</TD></TR> -<TR><TD ALIGN=center>i6</TD> - <TD ALIGN=center>fp</TD> - <TD ALIGN=center>frame pointer</TD></TR> -<TR><TD ALIGN=center>i7</TD> - <TD ALIGN=center>NA</TD> - <TD ALIGN=center>return address</TD></TR> - </TABLE> -</CENTER> -@end html -@end ifset - - -@subsection Floating Point Registers - -The SPARC V7 architecture includes thirty-two, -thirty-two bit registers. These registers may be viewed as -follows: - -@itemize @bullet -@item 32 single precision floating point or integer registers -(f0, f1, ... f31) - -@item 16 double precision floating point registers (f0, f2, -f4, ... f30) - -@item 8 extended precision floating point registers (f0, f4, -f8, ... f28) -@end itemize - -The floating point status register (fpsr) specifies -the behavior of the floating point unit for rounding, contains -its condition codes, version specification, and trap information. - -A queue of the floating point instructions which have -started execution but not yet completed is maintained. This -queue is needed to support the multiple cycle nature of floating -point operations and to aid floating point exception trap -handlers. Once a floating point exception has been encountered, -the queue is frozen until it is emptied by the trap handler. -The floating point queue is loaded by launching instructions. -It is emptied normally when the floating point completes all -outstanding instructions and by floating point exception -handlers with the store double floating point queue (stdfq) -instruction. - -@subsection Special Registers - -The SPARC architecture includes two special registers -which are critical to the programming model: the Processor State -Register (psr) and the Window Invalid Mask (wim). The psr -contains the condition codes, processor interrupt level, trap -enable bit, supervisor mode and previous supervisor mode bits, -version information, floating point unit and coprocessor enable -bits, and the current window pointer (cwp). The cwp field of -the psr and wim register are used to manage the register windows -in the SPARC architecture. The register windows are discussed -in more detail below. - -@section Register Windows - -The SPARC architecture includes the concept of -register windows. An overly simplistic way to think of these -windows is to imagine them as being an infinite supply of -"fresh" register sets available for each subroutine to use. In -reality, they are much more complicated. - -The save instruction is used to obtain a new register -window. This instruction decrements the current window pointer, -thus providing a new set of registers for use. This register -set includes eight fresh local registers for use exclusively by -this subroutine. When done with a register set, the restore -instruction increments the current window pointer and the -previous register set is once again available. - -The two primary issues complicating the use of -register windows are that (1) the set of register windows is -finite, and (2) some registers are shared between adjacent -registers windows. - -Because the set of register windows is finite, it is -possible to execute enough save instructions without -corresponding restore's to consume all of the register windows. -This is easily accomplished in a high level language because -each subroutine typically performs a save instruction upon -entry. Thus having a subroutine call depth greater than the -number of register windows will result in a window overflow -condition. The window overflow condition generates a trap which -must be handled in software. The window overflow trap handler -is responsible for saving the contents of the oldest register -window on the program stack. - -Similarly, the subroutines will eventually complete -and begin to perform restore's. If the restore results in the -need for a register window which has previously been written to -memory as part of an overflow, then a window underflow condition -results. Just like the window overflow, the window underflow -condition must be handled in software by a trap handler. The -window underflow trap handler is responsible for reloading the -contents of the register window requested by the restore -instruction from the program stack. - -The Window Invalid Mask (wim) and the Current Window -Pointer (cwp) field in the psr are used in conjunction to manage -the finite set of register windows and detect the window -overflow and underflow conditions. The cwp contains the index -of the register window currently in use. The save instruction -decrements the cwp modulo the number of register windows. -Similarly, the restore instruction increments the cwp modulo the -number of register windows. Each bit in the wim represents -represents whether a register window contains valid information. -The value of 0 indicates the register window is valid and 1 -indicates it is invalid. When a save instruction causes the cwp -to point to a register window which is marked as invalid, a -window overflow condition results. Conversely, the restore -instruction may result in a window underflow condition. - -Other than the assumption that a register window is -always available for trap (i.e. interrupt) handlers, the SPARC -architecture places no limits on the number of register windows -simultaneously marked as invalid (i.e. number of bits set in the -wim). However, RTEMS assumes that only one register window is -marked invalid at a time (i.e. only one bit set in the wim). -This makes the maximum possible number of register windows -available to the user while still meeting the requirement that -window overflow and underflow conditions can be detected. - -The window overflow and window underflow trap -handlers are a critical part of the run-time environment for a -SPARC application. The SPARC architectural specification allows -for the number of register windows to be any power of two less -than or equal to 32. The most common choice for SPARC -implementations appears to be 8 register windows. This results -in the cwp ranging in value from 0 to 7 on most implementations. - - -The second complicating factor is the sharing of -registers between adjacent register windows. While each -register window has its own set of local registers, the input -and output registers are shared between adjacent windows. The -output registers for register window N are the same as the input -registers for register window ((N - 1) modulo RW) where RW is -the number of register windows. An alternative way to think of -this is to remember how parameters are passed to a subroutine on -the SPARC. The caller loads values into what are its output -registers. Then after the callee executes a save instruction, -those parameters are available in its input registers. This is -a very efficient way to pass parameters as no data is actually -moved by the save or restore instructions. - -@section Call and Return Mechanism - -The SPARC architecture supports a simple yet -effective call and return mechanism. A subroutine is invoked -via the call (call) instruction. This instruction places the -return address in the caller's output register 7 (o7). After -the callee executes a save instruction, this value is available -in input register 7 (i7) until the corresponding restore -instruction is executed. - -The callee returns to the caller via a jmp to the -return address. There is a delay slot following this -instruction which is commonly used to execute a restore -instruction -- if a register window was allocated by this -subroutine. - -It is important to note that the SPARC subroutine -call and return mechanism does not automatically save and -restore any registers. This is accomplished via the save and -restore instructions which manage the set of registers windows. - -@section Calling Mechanism - -All RTEMS directives are invoked using the regular -SPARC calling convention via the call instruction. - -@section Register Usage - -As discussed above, the call instruction does not -automatically save any registers. The save and restore -instructions are used to allocate and deallocate register -windows. When a register window is allocated, the new set of -local registers are available for the exclusive use of the -subroutine which allocated this register set. - -@section Parameter Passing - -RTEMS assumes that arguments are placed in the -caller's output registers with the first argument in output -register 0 (o0), the second argument in output register 1 (o1), -and so forth. Until the callee executes a save instruction, the -parameters are still visible in the output registers. After the -callee executes a save instruction, the parameters are visible -in the corresponding input registers. The following pseudo-code -illustrates the typical sequence used to call a RTEMS directive -with three (3) arguments: - -@example -load third argument into o2 -load second argument into o1 -load first argument into o0 -invoke directive -@end example - -@section User-Provided Routines - -All user-provided routines invoked by RTEMS, such as -user extensions, device drivers, and MPCI routines, must also -adhere to these calling conventions. - |