Ivar Fatland
110 lines
3.4 KiB
ArmAsm
110 lines
3.4 KiB
ArmAsm
// SPDX-License-Identifier: Apache-2.0
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// SPDX-FileCopyrightText: 2026 The Ebitengine Authors
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//go:build linux
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#include "textflag.h"
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#include "go_asm.h"
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#include "funcdata.h"
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// S390X ELF ABI callbackasm1 implementation
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// On entry, R0 contains the callback index (set by callbackasm)
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// NOTE: We use R0 instead of R11 because R11 is callee-saved on S390X.
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//
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// S390X stack frame layout:
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// 0(R15) - back chain
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// 48(R15) - register save area (R6-R15)
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// 160(R15) - parameter area
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//
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// S390X uses R2-R6 for integer arguments (5 registers) and F0,F2,F4,F6 for floats (4 registers).
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//
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// Our frame layout (total 264 bytes, 8-byte aligned):
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// 0(R15) - back chain
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// 48(R15) - saved R6-R15 (done by STMG)
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// 160(R15) - callbackArgs struct (32 bytes: index, args, result, stackArgs)
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// 192(R15) - args array start
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//
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// Args array layout:
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// - floats F0,F2,F4,F6 (32 bytes)
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// - ints R2-R6 (40 bytes)
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// Total args array: 72 bytes, ends at 264
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//
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// Stack args in caller's frame start at old_R15+160
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#define FRAME_SIZE 264
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#define CB_ARGS 160
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#define ARGS_ARRAY 192
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#define FLOAT_OFF 0
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#define INT_OFF 32
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TEXT callbackasm1(SB), NOSPLIT|NOFRAME, $0
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NO_LOCAL_POINTERS
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// On entry, the trampoline in zcallback_s390x.s left
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// the callback index in R0 (NOT R11, since R11 is callee-saved).
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// R6 contains the 5th integer argument.
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// Save R6-R15 in caller's frame (per S390X ABI) BEFORE allocating our frame
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// STMG stores R6's current value (the 5th arg) at 48(R15)
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STMG R6, R15, 48(R15)
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// Save current stack pointer (will be back chain)
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MOVD R15, R1
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// Allocate our stack frame
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SUB $FRAME_SIZE, R15
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MOVD R1, 0(R15) // back chain
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// Save R0 (callback index) immediately - it's volatile
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MOVD R0, (CB_ARGS+0)(R15)
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// Save callback arguments to args array.
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// Layout: floats first (F0,F2,F4,F6), then ints (R2-R6)
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FMOVD F0, (ARGS_ARRAY+FLOAT_OFF+0*8)(R15)
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FMOVD F2, (ARGS_ARRAY+FLOAT_OFF+1*8)(R15)
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FMOVD F4, (ARGS_ARRAY+FLOAT_OFF+2*8)(R15)
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FMOVD F6, (ARGS_ARRAY+FLOAT_OFF+3*8)(R15)
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MOVD R2, (ARGS_ARRAY+INT_OFF+0*8)(R15)
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MOVD R3, (ARGS_ARRAY+INT_OFF+1*8)(R15)
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MOVD R4, (ARGS_ARRAY+INT_OFF+2*8)(R15)
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MOVD R5, (ARGS_ARRAY+INT_OFF+3*8)(R15)
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// R6 (5th int arg) was saved at 48(old_R15) by STMG
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// old_R15 = current R15 + FRAME_SIZE, so R6 is at 48+FRAME_SIZE(R15) = 312(R15)
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MOVD (48+FRAME_SIZE)(R15), R1
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MOVD R1, (ARGS_ARRAY+INT_OFF+4*8)(R15)
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// Finish setting up callbackArgs struct at CB_ARGS(R15)
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// struct { index uintptr; args unsafe.Pointer; result uintptr; stackArgs unsafe.Pointer }
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// Note: index was already saved earlier
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ADD $ARGS_ARRAY, R15, R1
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MOVD R1, (CB_ARGS+8)(R15) // args = address of register args
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MOVD $0, (CB_ARGS+16)(R15) // result = 0
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// stackArgs points to caller's stack arguments at old_R15+160 = R15+FRAME_SIZE+160
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ADD $(FRAME_SIZE+160), R15, R1
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MOVD R1, (CB_ARGS+24)(R15) // stackArgs = &caller_stack_args
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// Call crosscall2 with arguments in registers:
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// R2 = fn (from callbackWrap_call closure)
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// R3 = frame (address of callbackArgs)
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// R5 = ctxt (0)
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MOVD ·callbackWrap_call(SB), R2
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MOVD (R2), R2 // dereference closure to get fn
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ADD $CB_ARGS, R15, R3 // frame = &callbackArgs
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MOVD $0, R5 // ctxt = 0
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BL crosscall2(SB)
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// Get callback result into R2
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MOVD (CB_ARGS+16)(R15), R2
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// Deallocate frame
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ADD $FRAME_SIZE, R15
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// Restore R6-R15 from caller's frame
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LMG 48(R15), R6, R15
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RET
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