doc/vbccppc.texi - vbcc - Gitiles

 This chapter documents the Backend for the PowerPC processor family.

 @section Additional options for this version

 This backend provides the following additional options:

 @table @option

     @item -amiga-align

                 Do not require any alignments greater than 2 bytes.
                 This is needed when accessing Amiga system-structures, but
                 can cause a performance penalty.

     @item -baserel32mos

                 Use 32bit base-relative addressing as used by MorphOS.

     @item -baserel32os4

                 Use 32bit base-relative addressing as used by AmigaOS 4.

     @item -const-in-data

                 By default constant data will be placed in the @code{.rodata}
                 section. Using this option it will be placed in the
                 @code{.data} section.
                 Note that on operating systems with memory protection this
                 option will disable write-protection of constant data.

     @item -eabi
                Use the PowerPC Embedded ABI (eabi).

     @item -elf

                 Do not prefix symbols with '_'. Prefix labels with '.'.

     @item -fsub-zero

                 Use fsub to load a floating-point-register with zero.
                 This is faster but requires all registers to always contain
                 valid values (i.e. no NaNs etc.) which may not be the case
                 depending on startup-code, libraries etc.

     @item -gas
                 Create code suitable for the GNU assembler.

     @item -madd
                Use the @code{fmadd/fmsub} instructions for combining
                 multiplication with addition/subtraction in one instruction.
                 As these instructions do not round between the operations,
                 they have increased precision over separate addition and
                 multiplication.

                 While this usually does no harm, it is not ISO conforming
                 and therefore not the default behaviour.

     @item -merge-constants

                 Place identical floating point constants at the same
                 memory location. This can reduce program size.

     @item -no-align-args

                 Do not align function arguments on the stack stricter
                 than 4 bytes. Default with @option{-poweropen}.

     @item -no-peephole

                 Do not perform several peephole optimizations.
                 Currently includes:
                 @itemize @minus
                  @item better use of d16(r) addressing
                  @item use of indexed addressing modes
                  @item use of update-flag
                  @item use of record-flag
                  @item use of condition-code-registers to avoid certain branches
                 @end itemize

     @item -no-regnames

                 Do not use register names but only numbers in the assembly
                 output. This is necessary
                 to avoid name-conflicts when using @option{-elf}.

     @item -poweropen

                 Generate code for the PowerOpen ABI like used in AIX.
                 This does not work correctly yet.

     @item -sc

                 Generate code for the modified PowerOpen ABI used in the
                 StormC compiler (aka WarpOS ABI).

     @item -sd
                  Place all objects in small data-sections.

     @item -setccs

                 The V.4 ABI requires signalling (in a bit of the condition code
                 register) when arguments to varargs-functions
                 are passed in floating-point registers.
                 vbcc usually does not make use of this and
                 therefore does not set that bit by default.
                 This may lead to problems when linking objects compiled by
                 vbcc to objects/libraries created by other
                 compilers and calling varargs-functions with floating-point
                 arguments.
                 @option{-setccs} will fix this problem.

     @item -use-commons

                 Use real common symbols instead of bss symbols for
                 non-initialized external variables.

     @item -use-lmw

                 Use @code{lmw/stmw}-instructions. This can significantly reduce
                 code-size. However these instructions may be slower on
                 certain PPCs.

 @end table

 @section ABI

         This backend supports the following registers:

         @itemize @minus
         @item @code{r0} through @code{r31} for the general purpose registers,
         @item @code{f0} through @code{f31} for the floating point registers and
         @item @code{cr0} through @code{cr7} for the condition-code registers.
         @end itemize

         Additionally, the register pairs @code{r3/r4, r5/r6, r7/r8, r9/r10,
         r14/r15, r16/r17, r18/r19,
         r20/r21, r22/r23, r24/r25, r26/r27, r28/r29} and @code{r30/r31} are
         available.

         @code{r0, r11, r12, f0, f12} and @code{f13} are reserved by the
         backend.


     The current version generates assembly output for use with @file{vasmppc}
     or the GNU assembler. The generated code should
     work on 32bit systems based on a PowerPC CPU using the V.4 ABI or the
     PowerPC Embedded ABI (eabi).


     The registers r0, r3-r12, f0-f13 and cr0-cr1 are used as scratch registers
     (i.e. they can be destroyed in function calls), all other registers are
     preserved. r1 is the stack-pointer and r13 is the small-data-pointer if
     small-data-mode is used.

     The first 8 function arguments which have integer or pointer types
     are passed in registers r3 through r10 and the first 8 floating-point
     arguments are passed in registers f1 through f8. All other arguments
     are passed on the stack.

     Integers and pointers are returned in r3 (and r4 for long long),
     floats and doubles in f1.
     All other types are returned by passing the function the address
     of the result as a hidden argument - so when you call such a function
     without a proper declaration in scope you can expect a crash.

     The elementary data types are represented like:

     @example
     type        size in bits        alignment in bytes (-amiga-align)

     char                8                       1 (1)
     short              16                       2 (2)
     int                32                       4 (2)
     long               32                       4 (2)
     long long          64                       8 (2)
     all pointers       32                       4 (2)
     float              32                       4 (2)
     double             64                       8 (2)
     @end example

 @section Target-specific variable-attributes

     The PPC-backend offers the following variable-attributes:

 @table @code

     @item __saveds
                     Load the pointer to the small data segment at
                  function-entry. Applicable only to functions.

     @item __chip
                       Place variable in chip-memory. Only applicable on
                  AmigaOS to variables with static storage-duration.

     @item __far
                        Do not place this variable in the small-data segment
                  in small-data-mode. No effect in large-data-mode.
                  Only applicable to variables with static storage-
                  duration.

     @item __near
               Currently ignored.

     @item __saveall
                 Make sure all registers are saved by this function. On lower
                 optimization levels, all volatile registers will be saved
                 additionally. On higher levels, only the ones that may be
                 destroyed, are saved.

     @item __interrupt
                 Return with en @code{rfi}-instruction rather than @code{blr}.

     @item __section("name","attr")
                  Place this function/object in section "name" with
                  attributes "attr".
 @end table


 @section Target-specific pragmas

     The PPC-backend offers the following #pragmas:

 @table @code

     @item #pragma amiga-align
              Set alignment like -amiga-alignment option.

     @item #pragma natural-align
            Align every type to its own size.

     @item #pragma default-align
            Set alignment according to command-line options.

 @end table

 @section Predefined Macros

         This backend defines the following macros:

 @table @code
         @item __PPC__

         @item __AMIGADATE__
                 This is set to current date as @code{"(DD.MM.YYYY)"},
                 useful with version strings.
 @end table

 @section Stack

     If the @option{-stack-check} option is used, every function-prologue will
     call the function @code{__stack_check} with the stacksize needed by this
     function in register r12. This function has to consider its own
     stacksize and must restore all registers.

 @section Stdarg

     A possible <stdarg.h> for V.4 ABI could look like this:

 @example

 typedef struct @{
   int gpr;
   int fpr;
   char *regbase;
   char *membase;
 @} va_list;

 char *__va_start(void);
 char *__va_regbase(void);
 int __va_fixedgpr(void);
 int __va_fixedfpr(void);

 #define va_start(vl,dummy) \
   ( \
     vl.gpr=__va_fixedgpr(), \
     vl.fpr=__va_fixedfpr(), \
     vl.regbase=__va_regbase(), \
     vl.membase=__va_start() \
   )

 #define va_end(vl) ((vl).regbase=(vl).membase=0)

 #define va_copy(new,old) ((new)=(old))

 #define __va_align(type) (__alignof(type)>=4?__alignof(type):4)

 #define __va_do_align(vl,type) ((vl).membase=(char *)((((unsigned int)((vl).membase))+__va_align(type)-1)/__va_align(type)*__va_align(type)))

 #define __va_mem(vl,type) (__va_do_align((vl),type),(vl).membase+=sizeof(type),((type*)((vl).membase))[-1])

 #define va_arg(vl,type) \
  ( \
   (__typeof(type)&127)>10? \
     __va_mem((vl),type) \
   : \
    ( \
     (((__typeof(type)&127)>=6&&(__typeof(type)&127)<=8)) ? \
      ( \
       ++(vl).fpr<=8 ? \
         ((type*)((vl).regbase+32))[(vl).fpr-1] \
       : \
         __va_mem((vl),type) \
      ) \
     : \
      ( \
       ++(vl).gpr<=8 ? \
         ((type*)((vl).regbase+0))[(vl).gpr-1] \
       : \
         __va_mem((vl),type) \
      ) \
    ) \
  )

 @end example

     A possible <stdarg.h> for PowerOpen ABI could look like this:

 @example

 typedef unsigned char *va_list;

 #define __va_align(type) (4)

 #define __va_do_align(vl,type) ((vl)=(char *)((((unsigned int)(vl))+__va_align(type)-1)/__va_align(type)*__va_align(type)))

 #define __va_mem(vl,type) (__va_do_align((vl),type),(vl)+=sizeof(type),((type*)(vl))[-1])

 #define va_start(ap, lastarg) ((ap)=(va_list)(&lastarg+1))

 #define va_arg(vl,type) __va_mem(vl,type)

 #define va_end(vl) ((vl)=0)

 #define va_copy(new,old) ((new)=(old))

 @end example


 @section Known problems

 @itemize @minus
   @item  composite types are put on the stack rather than passed via pointer
   @item indication of fp-register-args with bit 6 of cr is not done well
 @end itemize
	This chapter documents the Backend for the PowerPC processor family.

	@section Additional options for this version

	This backend provides the following additional options:

	@table @option

	@item -amiga-align

	Do not require any alignments greater than 2 bytes.
	This is needed when accessing Amiga system-structures, but
	can cause a performance penalty.

	@item -baserel32mos

	Use 32bit base-relative addressing as used by MorphOS.

	@item -baserel32os4

	Use 32bit base-relative addressing as used by AmigaOS 4.

	@item -const-in-data

	By default constant data will be placed in the @code{.rodata}
	section. Using this option it will be placed in the
	@code{.data} section.
	Note that on operating systems with memory protection this
	option will disable write-protection of constant data.

	@item -eabi
	Use the PowerPC Embedded ABI (eabi).

	@item -elf

	Do not prefix symbols with '_'. Prefix labels with '.'.

	@item -fsub-zero

	Use fsub to load a floating-point-register with zero.
	This is faster but requires all registers to always contain
	valid values (i.e. no NaNs etc.) which may not be the case
	depending on startup-code, libraries etc.

	@item -gas
	Create code suitable for the GNU assembler.

	@item -madd
	Use the @code{fmadd/fmsub} instructions for combining
	multiplication with addition/subtraction in one instruction.
	As these instructions do not round between the operations,
	they have increased precision over separate addition and
	multiplication.

	While this usually does no harm, it is not ISO conforming
	and therefore not the default behaviour.

	@item -merge-constants

	Place identical floating point constants at the same
	memory location. This can reduce program size.

	@item -no-align-args

	Do not align function arguments on the stack stricter
	than 4 bytes. Default with @option{-poweropen}.

	@item -no-peephole

	Do not perform several peephole optimizations.
	Currently includes:
	@itemize @minus
	@item better use of d16(r) addressing
	@item use of indexed addressing modes
	@item use of update-flag
	@item use of record-flag
	@item use of condition-code-registers to avoid certain branches
	@end itemize

	@item -no-regnames

	Do not use register names but only numbers in the assembly
	output. This is necessary
	to avoid name-conflicts when using @option{-elf}.

	@item -poweropen

	Generate code for the PowerOpen ABI like used in AIX.
	This does not work correctly yet.

	@item -sc

	Generate code for the modified PowerOpen ABI used in the
	StormC compiler (aka WarpOS ABI).

	@item -sd
	Place all objects in small data-sections.

	@item -setccs

	The V.4 ABI requires signalling (in a bit of the condition code
	register) when arguments to varargs-functions
	are passed in floating-point registers.
	vbcc usually does not make use of this and
	therefore does not set that bit by default.
	This may lead to problems when linking objects compiled by
	vbcc to objects/libraries created by other
	compilers and calling varargs-functions with floating-point
	arguments.
	@option{-setccs} will fix this problem.

	@item -use-commons

	Use real common symbols instead of bss symbols for
	non-initialized external variables.

	@item -use-lmw

	Use @code{lmw/stmw}-instructions. This can significantly reduce
	code-size. However these instructions may be slower on
	certain PPCs.

	@end table

	@section ABI

	This backend supports the following registers:

	@itemize @minus
	@item @code{r0} through @code{r31} for the general purpose registers,
	@item @code{f0} through @code{f31} for the floating point registers and
	@item @code{cr0} through @code{cr7} for the condition-code registers.
	@end itemize

	Additionally, the register pairs @code{r3/r4, r5/r6, r7/r8, r9/r10,
	r14/r15, r16/r17, r18/r19,
	r20/r21, r22/r23, r24/r25, r26/r27, r28/r29} and @code{r30/r31} are
	available.

	@code{r0, r11, r12, f0, f12} and @code{f13} are reserved by the
	backend.



	The current version generates assembly output for use with @file{vasmppc}
	or the GNU assembler. The generated code should
	work on 32bit systems based on a PowerPC CPU using the V.4 ABI or the
	PowerPC Embedded ABI (eabi).


	The registers r0, r3-r12, f0-f13 and cr0-cr1 are used as scratch registers
	(i.e. they can be destroyed in function calls), all other registers are
	preserved. r1 is the stack-pointer and r13 is the small-data-pointer if
	small-data-mode is used.

	The first 8 function arguments which have integer or pointer types
	are passed in registers r3 through r10 and the first 8 floating-point
	arguments are passed in registers f1 through f8. All other arguments
	are passed on the stack.

	Integers and pointers are returned in r3 (and r4 for long long),
	floats and doubles in f1.
	All other types are returned by passing the function the address
	of the result as a hidden argument - so when you call such a function
	without a proper declaration in scope you can expect a crash.

	The elementary data types are represented like:

	@example
	type size in bits alignment in bytes (-amiga-align)

	char 8 1 (1)
	short 16 2 (2)
	int 32 4 (2)
	long 32 4 (2)
	long long 64 8 (2)
	all pointers 32 4 (2)
	float 32 4 (2)
	double 64 8 (2)
	@end example

	@section Target-specific variable-attributes

	The PPC-backend offers the following variable-attributes:

	@table @code

	@item __saveds
	Load the pointer to the small data segment at
	function-entry. Applicable only to functions.

	@item __chip
	Place variable in chip-memory. Only applicable on
	AmigaOS to variables with static storage-duration.

	@item __far
	Do not place this variable in the small-data segment
	in small-data-mode. No effect in large-data-mode.
	Only applicable to variables with static storage-
	duration.

	@item __near
	Currently ignored.

	@item __saveall
	Make sure all registers are saved by this function. On lower
	optimization levels, all volatile registers will be saved
	additionally. On higher levels, only the ones that may be
	destroyed, are saved.

	@item __interrupt
	Return with en @code{rfi}-instruction rather than @code{blr}.

	@item __section("name","attr")
	Place this function/object in section "name" with
	attributes "attr".
	@end table


	@section Target-specific pragmas

	The PPC-backend offers the following #pragmas:

	@table @code

	@item #pragma amiga-align
	Set alignment like -amiga-alignment option.

	@item #pragma natural-align
	Align every type to its own size.

	@item #pragma default-align
	Set alignment according to command-line options.

	@end table

	@section Predefined Macros

	This backend defines the following macros:

	@table @code
	@item __PPC__

	@item __AMIGADATE__
	This is set to current date as @code{"(DD.MM.YYYY)"},
	useful with version strings.
	@end table

	@section Stack

	If the @option{-stack-check} option is used, every function-prologue will
	call the function @code{__stack_check} with the stacksize needed by this
	function in register r12. This function has to consider its own
	stacksize and must restore all registers.

	@section Stdarg

	A possible <stdarg.h> for V.4 ABI could look like this:

	@example

	typedef struct @{
	int gpr;
	int fpr;
	char *regbase;
	char *membase;
	@} va_list;

	char *__va_start(void);
	char *__va_regbase(void);
	int __va_fixedgpr(void);
	int __va_fixedfpr(void);

	#define va_start(vl,dummy) \
	( \
	vl.gpr=__va_fixedgpr(), \
	vl.fpr=__va_fixedfpr(), \
	vl.regbase=__va_regbase(), \
	vl.membase=__va_start() \
	)

	#define va_end(vl) ((vl).regbase=(vl).membase=0)

	#define va_copy(new,old) ((new)=(old))

	#define __va_align(type) (__alignof(type)>=4?__alignof(type):4)

	#define __va_do_align(vl,type) ((vl).membase=(char )((((unsigned int)((vl).membase))+__va_align(type)-1)/__va_align(type)__va_align(type)))

	#define __va_mem(vl,type) (__va_do_align((vl),type),(vl).membase+=sizeof(type),((type*)((vl).membase))[-1])

	#define va_arg(vl,type) \
	( \
	(__typeof(type)&127)>10? \
	__va_mem((vl),type) \
	: \
	( \
	(((__typeof(type)&127)>=6&&(__typeof(type)&127)<=8)) ? \
	( \
	++(vl).fpr<=8 ? \
	((type*)((vl).regbase+32))[(vl).fpr-1] \
	: \
	__va_mem((vl),type) \
	) \
	: \
	( \
	++(vl).gpr<=8 ? \
	((type*)((vl).regbase+0))[(vl).gpr-1] \
	: \
	__va_mem((vl),type) \
	) \
	) \
	)

	@end example

	A possible <stdarg.h> for PowerOpen ABI could look like this:

	@example

	typedef unsigned char *va_list;

	#define __va_align(type) (4)

	#define __va_do_align(vl,type) ((vl)=(char )((((unsigned int)(vl))+__va_align(type)-1)/__va_align(type)__va_align(type)))

	#define __va_mem(vl,type) (__va_do_align((vl),type),(vl)+=sizeof(type),((type*)(vl))[-1])

	#define va_start(ap, lastarg) ((ap)=(va_list)(&lastarg+1))

	#define va_arg(vl,type) __va_mem(vl,type)

	#define va_end(vl) ((vl)=0)

	#define va_copy(new,old) ((new)=(old))

	@end example


	@section Known problems

	@itemize @minus
	@item composite types are put on the stack rather than passed via pointer
	@item indication of fp-register-args with bit 6 of cr is not done well
	@end itemize