newlib-cygwin/newlib/libc/machine/arm/setjmp.S

/* This is a simple version of setjmp and longjmp.

   Nick Clifton, Cygnus Solutions, 13 June 1997.  */

/* ANSI concatenation macros.  */
#define CONCAT(a, b)  CONCAT2(a, b)
#define CONCAT2(a, b) a##b

#ifndef __USER_LABEL_PREFIX__
#error  __USER_LABEL_PREFIX__ not defined
#endif

#define SYM(x) CONCAT (__USER_LABEL_PREFIX__, x)

#ifdef __ELF__
#define TYPE(x) .type SYM(x),function
#define SIZE(x) .size SYM(x), . - SYM(x)
#else
#define TYPE(x)
#define SIZE(x)
#endif

/* Arm/Thumb interworking support:

   The interworking scheme expects functions to use a BX instruction
   to return control to their parent.  Since we need this code to work
   in both interworked and non-interworked environments as well as with
   older processors which do not have the BX instruction we do the 
   following:
	Test the return address.
	If the bottom bit is clear perform an "old style" function exit.
	(We know that we are in ARM mode and returning to an ARM mode caller).
	Otherwise use the BX instruction to perform the function exit.

   We know that we will never attempt to perform the BX instruction on 
   an older processor, because that kind of processor will never be 
   interworked, and a return address with the bottom bit set will never 
   be generated.

   In addition, we do not actually assemble the BX instruction as this would
   require us to tell the assembler that the processor is an ARM7TDMI and
   it would store this information in the binary.  We want this binary to be
   able to be linked with binaries compiled for older processors however, so
   we do not want such information stored there.  

   If we are running using the APCS-26 convention however, then we never
   test the bottom bit, because this is part of the processor status.  
   Instead we just do a normal return, since we know that we cannot be 
   returning to a Thumb caller - the Thumb does not support APCS-26.
	
   Function entry is much simpler.  If we are compiling for the Thumb we 
   just switch into ARM mode and then drop through into the rest of the
   function.  The function exit code will take care of the restore to
   Thumb mode.  */

#ifdef __APCS_26__
#define RET	movs		pc, lr
#else
#define RET	tst		lr, #1; \
	        moveq		pc, lr ; \
.word           0xe12fff1e	/* bx lr */
#endif

#ifdef __thumb__
#define	MODE		.thumb_func
.macro PROLOGUE name
	.code 16
	bx	pc
	nop	
	.code 32
SYM (.arm_start_of.\name):
.endm
#else
#define	MODE		.code 32
.macro PROLOGUE name
.endm
#endif
	
.macro FUNC_START name
	.text
	.align 2
	MODE
	.globl SYM (\name)
	TYPE (\name)
SYM (\name):
	PROLOGUE \name
.endm

.macro FUNC_END name
	RET
	SIZE (\name)
.endm
	
/* --------------------------------------------------------------------
                 int setjmp (jmp_buf); 
   -------------------------------------------------------------------- */
	
	FUNC_START setjmp

	/* Save all the callee-preserved registers into the jump buffer.  */
	stmea		a1!, { v1-v7, fp, ip, sp, lr }
	
#if 0	/* Simulator does not cope with FP instructions yet.  */
#ifndef __SOFTFP__
	/* Save the floating point registers.  */
	sfmea		f4, 4, [a1]
#endif
#endif		
	/* When setting up the jump buffer return 0.  */
	mov		a1, #0

	FUNC_END setjmp
	
/* --------------------------------------------------------------------
		volatile void longjmp (jmp_buf, int);
   -------------------------------------------------------------------- */
	
	FUNC_START longjmp

	/* If we have stack extension code it ought to be handled here.  */
	
	/* Restore the registers, retrieving the state when setjmp() was called.  */
	ldmfd		a1!, { v1-v7, fp, ip, sp, lr }
	
#if 0	/* Simulator does not cope with FP instructions yet.  */
#ifndef __SOFTFP__
	/* Restore floating point registers as well.  */
	lfmfd		f4, 4, [a1]
#endif
#endif	
	/* Put the return value into the integer result register.
	   But if it is zero then return 1 instead.  */	
	movs		a1, a2
	moveq		a1, #1

	FUNC_END longjmp