STP 中的寄存器存储顺序
Order of register stores in STP
在 AArch64 程序集中，以下行
stp x25, x30, [sp,#48]
在 sp+48 处存储 x25，在 sp+56 处存储 x30，对吗？
是的。来自 this manual，第 C6-1237 页及以下内容：
Signed offset
[...]
64-bit variant
Applies when opc == 10.
STP <Xt1>, <Xt2>, [<Xn|SP>{, #<imm>}]
Decode for all variants of this encoding
boolean wback = FALSE;
boolean postindex = FALSE;
[...]
Shared decode for all encodings
[...]
integer n = UInt(Rn);
integer t = UInt(Rt);
integer t2 = UInt(Rt2);
[...]
integer scale = 2 + UInt(opc<1>);
integer datasize = 8 << scale;
bits(64) offset = LSL(SignExtend(imm7, 64), scale);
[...]
Operation for all encodings
constant integer dbytes = datasize DIV 8;
[...]
if n == 31 then
CheckSPAlignment();
address = SP[];
else
address = X[n];
if !postindex then
address = address + offset;
[...]
data1 = X[t];
[...]
data2 = X[t2];
Mem[address, dbytes, AccType_NORMAL] = data1;
Mem[address+dbytes, dbytes, AccType_NORMAL] = data2;
让我们从头到尾了解一下。您的 stp x25, x30, [sp,#48] 是 64 位的 signed-offset stp，解码为：
n = 31
t = 25
t2 = 30
scale = 3 // since opc = 0b10
datasize = 64
offset = 48
将其插入到操作伪代码中，用变量替换它们的值，您将有效地得到：
CheckSPAlignment();
Mem[SP[] + 48, 8, AccType_NORMAL] = X[25];
Mem[SP[] + 56, 8, AccType_NORMAL] = X[30];
在 AArch64 程序集中，以下行
stp x25, x30, [sp,#48]
在 sp+48 处存储 x25，在 sp+56 处存储 x30，对吗？
是的。来自 this manual，第 C6-1237 页及以下内容：
Signed offset
[...]
64-bit variant
Applies whenopc == 10.
STP <Xt1>, <Xt2>, [<Xn|SP>{, #<imm>}]Decode for all variants of this encoding
boolean wback = FALSE; boolean postindex = FALSE;[...]
Shared decode for all encodings
[...]integer n = UInt(Rn); integer t = UInt(Rt); integer t2 = UInt(Rt2); [...] integer scale = 2 + UInt(opc<1>); integer datasize = 8 << scale; bits(64) offset = LSL(SignExtend(imm7, 64), scale);[...]
Operation for all encodings
constant integer dbytes = datasize DIV 8; [...] if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n]; if !postindex then address = address + offset; [...] data1 = X[t]; [...] data2 = X[t2]; Mem[address, dbytes, AccType_NORMAL] = data1; Mem[address+dbytes, dbytes, AccType_NORMAL] = data2;
让我们从头到尾了解一下。您的 stp x25, x30, [sp,#48] 是 64 位的 signed-offset stp，解码为：
n = 31
t = 25
t2 = 30
scale = 3 // since opc = 0b10
datasize = 64
offset = 48
将其插入到操作伪代码中，用变量替换它们的值，您将有效地得到：
CheckSPAlignment();
Mem[SP[] + 48, 8, AccType_NORMAL] = X[25];
Mem[SP[] + 56, 8, AccType_NORMAL] = X[30];