github.com/afumu/libc@v0.0.6/musl/src/thread/powerpc/syscall_cp.s (about)

     1  .global __cp_begin
     2  .hidden __cp_begin
     3  .global __cp_end
     4  .hidden __cp_end
     5  .global __cp_cancel
     6  .hidden __cp_cancel
     7  .hidden __cancel
     8  .global __syscall_cp_asm
     9  .hidden __syscall_cp_asm
    10  
    11  #r0: volatile. may be modified during linkage.
    12  #r1: stack frame: 16 byte alignment.
    13  #r2: tls/thread pointer on pp32
    14  #r3,r4: return values, first args
    15  #r5-r10: args
    16  #r11-r12: volatile. may be modified during linkage
    17  #r13: "small data area" pointer
    18  #r14 - r30: local vars
    19  #r31: local or environment pointer
    20  
    21  #r1, r14-31: belong to the caller, must be saved and restored
    22  #r0, r3-r12, ctr, xer: volatile, not preserved
    23  #r0,r11,r12: may be altered by cross-module call, 
    24  #"a func cannot depend on that these regs have the values placed by the caller"
    25  
    26  #the fields CR2,CR2,CR4 of the cond reg must be preserved
    27  #LR (link reg) shall contain the funcs return address
    28  	.text
    29  	.type   __syscall_cp_asm,%function
    30  __syscall_cp_asm:
    31  	# at enter: r3 = pointer to self->cancel, r4: syscall no, r5: first arg, r6: 2nd, r7: 3rd, r8: 4th, r9: 5th, r10: 6th
    32  __cp_begin:
    33  	# r3 holds first argument, its a pointer to self->cancel. 
    34  	# we must compare the dereferenced value with 0 and jump to __cancel if its not
    35  	
    36  	lwz 0, 0(3) #deref pointer into r0
    37  	
    38  	cmpwi cr7, 0, 0 #compare r0 with 0, store result in cr7. 
    39  	beq+ cr7, 1f #jump to label 1 if r0 was 0
    40  	
    41  	b __cp_cancel #else call cancel
    42  1:
    43  	#ok, the cancel flag was not set
    44  	# syscall: number goes to r0, the rest 3-8
    45  	mr      0, 4                  # put the system call number into r0
    46  	mr      3, 5                  # Shift the arguments: arg1
    47  	mr      4, 6                  # arg2
    48  	mr      5, 7                  # arg3
    49  	mr      6, 8                  # arg4
    50  	mr      7, 9                  # arg5
    51  	mr      8, 10                  # arg6
    52  	sc
    53  __cp_end:
    54  	bnslr+ # return if no summary overflow. 
    55  	#else negate result.
    56  	neg 3, 3
    57  	blr
    58  __cp_cancel:
    59  	b __cancel