make_riscv64_sysv_elf_gas.S

/*
   Distributed under the Boost Software License, Version 1.0.
      (See accompanying file LICENSE_1_0.txt or copy at
          http://www.boost.org/LICENSE_1_0.txt)
*/
/*******************************************************
 *                                                     *
 *  -------------------------------------------------  *
 *  |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |  *
 *  -------------------------------------------------  *
 *  | 0x0 | 0x4 | 0x8 | 0xc | 0x10| 0x14| 0x18| 0x1c|  *
 *  -------------------------------------------------  *
 *  |    fs0    |    fs1    |    fs2    |    fs3    |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  8  |  9  |  10 |  11 |  12 |  13 |  14 |  15 |  *
 *  -------------------------------------------------  *
 *  | 0x20| 0x24| 0x28| 0x2c| 0x30| 0x34| 0x38| 0x3c|  *
 *  -------------------------------------------------  *
 *  |    fs4    |    fs5    |    fs6    |    fs7    |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  16 |  17 |  18 |  19 |  20 |  21 |  22 |  23 |  *
 *  -------------------------------------------------  *
 *  | 0x40| 0x44| 0x48| 0x4c| 0x50| 0x54| 0x58| 0x5c|  *
 *  -------------------------------------------------  *
 *  |    fs8    |    fs9    |    fs10   |    fs11   |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  24 |  25 |  26 |  27 |  28 |  29 |  30 |  31 |  *
 *  -------------------------------------------------  *
 *  | 0x60| 0x64| 0x68| 0x6c| 0x70| 0x74| 0x78| 0x7c|  *
 *  -------------------------------------------------  *
 *  |    s0     |    s1     |    s2     |    s3     |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  32 |  33 |  34 |  35 |  36 |  37 |  38 |  39 |  *
 *  -------------------------------------------------  *
 *  | 0x80| 0x84| 0x88| 0x8c| 0x90| 0x94| 0x98| 0x9c|  *
 *  -------------------------------------------------  *
 *  |    s4     |    s5     |    s6     |     s7    |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  40 |  41 |  42 | 43  |  44 | 45  |  46 | 47  |  *
 *  -------------------------------------------------  *
 *  | 0xa0| 0xa4| 0xa8| 0xac| 0xb0| 0xb4| 0xb8| 0xbc|  *
 *  -------------------------------------------------  *
 *  |     s8    |     s9    |    s10    |    s11    |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  48 |  49 |  50 | 51  |     |     |     |     |  *
 *  -------------------------------------------------  *
 *  | 0xc0| 0xc4| 0xc8| 0xcc|     |     |     |     |  *
 *  -------------------------------------------------  *
 *  |     ra    |     pc    |           |           |  *
 *  -------------------------------------------------  *
 *                                                     *
 *******************************************************/

.file "make_riscv64_sysv_elf_gas.S"
.text
.align  1
.global make_fcontext
.type   make_fcontext, %function
make_fcontext:
    # shift address in a0 (allocated stack) to lower 16 byte boundary
    andi a0, a0, ~0xF

    # reserve space for context-data on context-stack
    addi  a0, a0, -0xd0

    # third arg of make_fcontext() == address of context-function
    # store address as a PC to jump in
    sd  a2, 0xc8(a0)

    # save address of finish as return-address for context-function
    # will be entered after context-function returns (RA register)
    lla  a4, finish
    sd  a4, 0xc0(a0)

    ret // return pointer to context-data (a0)

finish:
    # exit code is zero
    li  a0, 0
    # exit application
    tail  _exit@plt

.size   make_fcontext,.-make_fcontext
# Mark that we don't need executable stack.
.section .note.GNU-stack,"",%progbits