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bsnes/libco/ppc-elf.c

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/*
* libco.ppc-elf
* author: Kernigh
* license: public domain
*
* PowerPC 32-bit ELF implementation of libco (for compile with GCC),
* ported from PowerPC Mac OS X implementation (ppc.s) by Vas Crabb.
* This ELF version works for OpenBSD, and might also work for FreeBSD,
* NetBSD and Linux.
*
* Note 1: This implementation does not handle the AltiVec/VMX
* registers, because the ELF ABI does not mention them,
* and my OpenBSD system is not using them.
*
* Note 2: If you want position-independent code, then you must
* define __PIC__. gcc -fpic or -fPIC defines __PIC__, but
* gcc -fpie or -fPIE might not. If you want to use -fpie
* or -fPIE, then you might need a manual definition:
* gcc -fpie -D__PIC__=1
* gcc -fPIE -D__PIC__=2
*
* The ELF ABI is "System V Application Binary Interface, PowerPC
* Processor Supplement", which you can get from
* <http://refspecs.linux-foundation.org/elf/elfspec_ppc.pdf>
* (PDF file, hosted by Linux Foundation).
*
* ELF and Mac OS X use similar conventions to allocate the registers,
* and to pass arguments and return values through registers. The main
* differences are that ELF has a slightly different stack format, that
* symbols are different (and without an extra underscore at the start),
* and that the assembly syntax is different.
*
* A function may destroy the values of volatile registers, but must
* preserve the values of nonvolatile registers. So the co_switch()
* function only saves the nonvolatile registers.
*
* [nonvolatile registers in ELF]
* %r1, %r14..%r31
* %f14..%f31
* %cr2..%cr4 in cr
*
* [volatile registers in ELF]
* %r0, %r3..%r10
* %f0..%f13
* %cr0, %cr1, %cr5..%cr7 in cr
* ctr, lr, xer
*
* lr (link register) is volatile, but it contains the return address,
* so co_switch must save lr.
*
* %r13 is the small data pointer. This is constant across threads, so
* co_switch() does not touch %r13.
*
* %r2 is a reserved register, so co_switch() does not touch %r2. Some
* systems might borrow an idea from the PowerPC Embedded ABI, and might
* use %r2 as a small read-only data pointer, which is constant across
* threads.
*/
#ifdef __cplusplus
extern "C" {
#endif
typedef void * cothread_t;
/*
* co_active_context is either in a global offset table (if we are
* compiling -fPIC or -fPIE) or has an absolute position.
*/
static void *co_main_stack_pointer;
static cothread_t co_active_context = &co_main_stack_pointer;
extern cothread_t co_active() {
return co_active_context;
}
/*
* Embedded assembly.
*
* We are not using the percent-sign substitution feature,
* so we must write "%r1", not "%%r1".
*
* We always write 'bl malloc@plt', not 'bl malloc'. The '@plt'
* is necessary in position-indepent code and seems to have no
* significant effect in fixed-position code.
*
* We never use the 'lmw' or 'stmw' instructions. The ELF ABI
* mentions that these instructions "are usually slower than
* a sequence of other instructions that have the same effect."
* We instead use sequences of 'lwz' or 'stz' instructions.
*/
__asm__("\n"
"### embedded assembly \n"
".section \".text\" \n"
" .balign 4 \n"
" \n"
/*
* void co_switch(co_thread to %r3)
*
* Allocate our stack frame of 240 bytes:
* Old New Value
* 4(%r1) 244(%r1) return address, used by us
* 0(%r1) 240(%r1) frame pointer
* 232(%r1) %f31
* 224(%r1) %f30
* ...
* 96(%r1) %f14
* 92(%r1) %r31
* 88(%r1) %r30
* ...
* 24(%r1) %r14
* 20(%r1) condition register
* 8(%r1) padding of 12 bytes
* 4(%r1) return address, never used
* 0(%r1) frame pointer
*
* Save our registers in our stack frame.
* Save our stack pointer in 0(%r4).
* Switch to the stack of the other thread.
* Restore registers and return.
*/
" .globl co_switch \n"
" .type co_switch, @function \n"
"co_switch: \n"
" mflr %r0 # %r0 = return address \n"
" mfcr %r9 # %r9 = condition register \n"
" stwu %r1, -240(%r1) # allocate stack frame \n"
" \n"
" stw %r0, 244(%r1) # save return address \n"
" stfd %f31, 232(%r1) # save floating-point regs \n"
" stfd %f30, 224(%r1) \n"
" stfd %f29, 216(%r1) \n"
" stfd %f28, 208(%r1) \n"
" stfd %f27, 200(%r1) \n"
" stfd %f26, 192(%r1) \n"
" stfd %f25, 184(%r1) \n"
" stfd %f24, 176(%r1) \n"
" stfd %f23, 168(%r1) \n"
" stfd %f22, 160(%r1) \n"
" stfd %f21, 152(%r1) \n"
" stfd %f20, 144(%r1) \n"
" stfd %f19, 136(%r1) \n"
" stfd %f18, 128(%r1) \n"
" stfd %f17, 120(%r1) \n"
" stfd %f16, 112(%r1) \n"
" stfd %f16, 104(%r1) \n"
" stfd %f14, 96(%r1) \n"
" stw %r31, 92(%r1) # save general-purpose regs \n"
" stw %r30, 88(%r1) \n"
" stw %r29, 84(%r1) \n"
" stw %r28, 80(%r1) \n"
" stw %r27, 76(%r1) \n"
" stw %r26, 72(%r1) \n"
" stw %r25, 68(%r1) \n"
" stw %r24, 64(%r1) \n"
" stw %r23, 60(%r1) \n"
" stw %r22, 56(%r1) \n"
" stw %r21, 52(%r1) \n"
" stw %r20, 48(%r1) \n"
" stw %r19, 44(%r1) \n"
" stw %r18, 40(%r1) \n"
" stw %r17, 36(%r1) \n"
" stw %r16, 32(%r1) \n"
" stw %r15, 28(%r1) \n"
" stw %r14, 24(%r1) \n"
" stw %r9, 20(%r1) # save condition reg \n"
" \n"
" # save current context, set new context \n"
" # %r4 = co_active_context \n"
" # co_active_context = %r3 \n"
#if __PIC__ == 2
" # position-independent code, large model (-fPIC) \n"
" bl _GLOBAL_OFFSET_TABLE_@local-4 \n"
" mflr %r8 # %r8 = address of got \n"
" addis %r7, %r8, co_active_context@got@ha \n"
" lwz %r6, co_active_context@got@l(%r7) \n"
" lwz %r4, 0(%r6) \n"
" stw %r3, 0(%r6) \n"
#elif __PIC__ == 1
" # position-independent code, small model (-fpic) \n"
" bl _GLOBAL_OFFSET_TABLE_@local-4 \n"
" mflr %r8 # %r8 = address of got \n"
" lwz %r7, co_active_context@got(%r8) \n"
" lwz %r4, 0(%r7) \n"
" stw %r3, 0(%r7) \n"
#else
" # fixed-position code \n"
" lis %r8, co_active_context@ha \n"
" lwz %r4, co_active_context@l(%r8) \n"
" stw %r3, co_active_context@l(%r8) \n"
#endif
" \n"
" # save current stack pointer \n"
" stw %r1, 0(%r4) \n"
" # get new stack pointer \n"
" lwz %r1, 0(%r3) \n"
" \n"
" lwz %r0, 244(%r1) # get return address \n"
" lfd %f31, 232(%r1) # restore floating-point regs \n"
" lfd %f30, 224(%r1) \n"
" lfd %f29, 216(%r1) \n"
" lfd %f28, 208(%r1) \n"
" lfd %f27, 200(%r1) \n"
" lfd %f26, 192(%r1) \n"
" lfd %f25, 184(%r1) \n"
" lfd %f24, 176(%r1) \n"
" lfd %f23, 168(%r1) \n"
" lfd %f22, 160(%r1) \n"
" lfd %f21, 152(%r1) \n"
" lfd %f20, 144(%r1) \n"
" lfd %f19, 136(%r1) \n"
" lfd %f18, 128(%r1) \n"
" lfd %f17, 120(%r1) \n"
" lfd %f16, 112(%r1) \n"
" lfd %f16, 104(%r1) \n"
" lfd %f14, 96(%r1) \n"
" lwz %r31, 92(%r1) # restore general-purpose regs \n"
" lwz %r30, 88(%r1) \n"
" lwz %r29, 84(%r1) \n"
" lwz %r28, 80(%r1) \n"
" lwz %r27, 76(%r1) \n"
" lwz %r26, 72(%r1) \n"
" lwz %r25, 68(%r1) \n"
" lwz %r24, 64(%r1) \n"
" lwz %r23, 60(%r1) \n"
" lwz %r22, 56(%r1) \n"
" lwz %r21, 52(%r1) \n"
" lwz %r20, 48(%r1) \n"
" lwz %r19, 44(%r1) \n"
" lwz %r18, 40(%r1) \n"
" lwz %r17, 36(%r1) \n"
" lwz %r16, 32(%r1) \n"
" lwz %r15, 28(%r1) \n"
" lwz %r14, 24(%r1) \n"
" lwz %r9, 20(%r1) # get condition reg \n"
" \n"
" addi %r1, %r1, 240 # free stack frame \n"
" mtlr %r0 # restore return address \n"
" mtcr %r9 # restore condition register \n"
" blr # return \n"
" .size co_switch, . - co_switch \n"
" \n"
/*
* cothread_t %r3 co_create(unsigned int stack_size %r3,
* void (*coentry %r4)())
*
* Allocate a new stack, such that when you co_switch to that
* stack, then co_switch returns to coentry.
*/
" .globl co_create \n"
" .type co_create, @function \n"
"co_create: \n"
" mflr %r0 # %r0 = return address \n"
" stwu %r1, -16(%r1) # allocate my stack frame \n"
" stw %r0, 20(%r1) # save return address \n"
" stw %r31, 12(%r1) # save %r31 \n"
" stw %r30, 8(%r1) # save %r30 \n"
" \n"
" mr %r30, %r3 # %r30 = stack_size \n"
" mr %r31, %r4 # %r31 = coentry \n"
" \n"
" # Call malloc(stack_size %r3) to allocate stack; \n"
" # malloc() probably uses good alignment. \n"
" # \n"
" bl malloc@plt # returns %r3 = low end \n"
" cmpwi %r3, 0 # if returned NULL, \n"
" beq- 1f # then abort \n"
" \n"
" # we return %r3 = low end of stack \n"
" add %r4, %r3, %r30 # %r4 = high end of stack \n"
" \n"
" # uncomment if malloc() uses wrong alignment \n"
" #rlwinm %r4,%r4,0,0,27 # force 16-byte alignment \n"
" \n"
/*
* Allocate two stack frames:
* 16 bytes for stack frame with return address
* 240 bytes for co_switch stack frame
*
* Old New Value
* -8(%r4) 248(%r5) padding of 8 bytes
* -12(%r4) 244(%r5) return address = coentry
* -16(%r4) 240(%r5) frame pointer = NULL
* 232(%r5) %f31 = 0
* ...
* 20(%r5) condition register = 0
* 0(%r5) frame pointer
*/
" li %r9, (240-20)/4+1 \n"
" addi %r5, %r4, -16 # allocate first stack frame \n"
" li %r0, 0 \n"
" stwu %r5, -240(%r5) # allocate second stack frame \n"
" li %r8, 20 \n"
" mtctr %r9 # loop %r9 times \n"
"2: # loop to store zero to 20(%r5) through 240(%r5) \n"
" stwx %r0, %r5, %r8 \n"
" addi %r8, %r8, 4 # index += 4 \n"
" bdnz+ 2b # ctr -= 1, branch if nonzero \n"
" \n"
" stw %r31, 244(%r5) # return address = coentry \n"
" stw %r5, 0(%r3) # save stack pointer \n"
" \n"
" lwz %r0, 20(%r1) # get return address \n"
" lwz %r31, 12(%r1) # restore %r31 \n"
" lwz %r30, 8(%r1) # restore %r30 \n"
" mtlr %r0 # restore return address \n"
" addi %r1, %r1, 16 # free stack frame \n"
" blr # return \n"
" \n"
"1: b abort@plt # branch 1f to abort \n"
" .size co_create, . - co_create \n"
" \n"
/*
* void co_delete(cothread_t) => void free(void *)
*/
" .globl co_delete \n"
" .type co_delete, @function \n"
"co_delete: \n"
" b free@plt \n"
" \n"
);
#ifdef __cplusplus
}
#endif
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