cm.push

Create function call stack frame

This instruction is defined by:

  • anyOf:

    • Zcmp, version >= 0

This instruction is included in the following profiles:

Encoding

svg

Assembly format

cm.push reg_list, -stack_adj

Synopsis

Create stack frame: store ra and 0 to 12 saved registers to the stack frame, optionally allocate additional stack space. This instruction pushes (stores) the registers in reg_list to the memory below the stack pointer, and then creates the stack frame by decrementing the stack pointer by stack_adj.

Restrictions on stack_adj:

  • it must be enough to store all of the listed registers

  • it must be a multiple of 16 (bytes):

    • for RV32 the allowed values are: 16, 32, 48, 64, 80, 96, 112

    • for RV64 the allowed values are: 16, 32, 48, 64, 80, 96, 112, 128, 144, 160

Access

M HS U VS VU

Always

Always

Always

Always

Always

Decode Variables

Bits<4> rlist = $encoding[7:4];
Bits<6> spimm = {$encoding[3:2], 4'd0};

Execution

  • IDL

if (implemented?(ExtensionName::Zcmp) && (CSR[misa].C == 1'b0)) {
  raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
XReg size = xlen();
XReg nreg = (rlist == 15) ? 13 : (rlist - 3);
XReg stack_aligned_adj = (nreg * 4 + 15) & ~0xF;
XReg virtual_address_sp = X[2];
XReg virtual_address_new_sp = virtual_address_sp - stack_aligned_adj - spimm;
XReg virtual_address_base = virtual_address_sp - (nreg * size);
write_memory_xlen(virtual_address_base + 0 * size, X[1], $encoding);
if (nreg > 1) {
  write_memory_xlen(virtual_address_base + 1 * size, X[8], $encoding);
}
if (nreg > 2) {
  write_memory_xlen(virtual_address_base + 2 * size, X[9], $encoding);
}
if (nreg > 3) {
  write_memory_xlen(virtual_address_base + 3 * size, X[18], $encoding);
}
if (nreg > 4) {
  write_memory_xlen(virtual_address_base + 4 * size, X[19], $encoding);
}
if (nreg > 5) {
  write_memory_xlen(virtual_address_base + 5 * size, X[20], $encoding);
}
if (nreg > 6) {
  write_memory_xlen(virtual_address_base + 6 * size, X[21], $encoding);
}
if (nreg > 7) {
  write_memory_xlen(virtual_address_base + 7 * size, X[22], $encoding);
}
if (nreg > 8) {
  write_memory_xlen(virtual_address_base + 8 * size, X[23], $encoding);
}
if (nreg > 9) {
  write_memory_xlen(virtual_address_base + 9 * size, X[24], $encoding);
}
if (nreg > 10) {
  write_memory_xlen(virtual_address_base + 10 * size, X[25], $encoding);
}
if (nreg > 11) {
  write_memory_xlen(virtual_address_base + 11 * size, X[26], $encoding);
  write_memory_xlen(virtual_address_base + 12 * size, X[27], $encoding);
}
X[2] = virtual_address_new_sp;

Exceptions

This instruction may result in the following synchronous exceptions:

  • IllegalInstruction

  • LoadAccessFault

  • StoreAmoAccessFault

  • StoreAmoPageFault