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    Subject[PATCH v4 07/18] tools/nolibc: arm: shrink _start with _start_c
    Date
    move most of the _start operations to _start_c(), include the
    stackprotector initialization.

    Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
    ---
    tools/include/nolibc/arch-arm.h | 44 ++++-----------------------------
    1 file changed, 5 insertions(+), 39 deletions(-)

    diff --git a/tools/include/nolibc/arch-arm.h b/tools/include/nolibc/arch-arm.h
    index a06dad789a22..cae4afa7c1c7 100644
    --- a/tools/include/nolibc/arch-arm.h
    +++ b/tools/include/nolibc/arch-arm.h
    @@ -8,6 +8,7 @@
    #define _NOLIBC_ARCH_ARM_H

    #include "compiler.h"
    +#include "crt.h"

    /* Syscalls for ARM in ARM or Thumb modes :
    * - registers are 32-bit
    @@ -183,49 +184,14 @@
    _arg1; \
    })

    -
    -char **environ __attribute__((weak));
    -const unsigned long *_auxv __attribute__((weak));
    -
    /* startup code */
    void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void)
    {
    __asm__ volatile (
    -#ifdef _NOLIBC_STACKPROTECTOR
    - "bl __stack_chk_init\n" /* initialize stack protector */
    -#endif
    - "pop {%r0}\n" /* argc was in the stack */
    - "mov %r1, %sp\n" /* argv = sp */
    -
    - "add %r2, %r0, $1\n" /* envp = (argc + 1) ... */
    - "lsl %r2, %r2, $2\n" /* * 4 ... */
    - "add %r2, %r2, %r1\n" /* + argv */
    - "ldr %r3, 1f\n" /* r3 = &environ (see below) */
    - "str %r2, [r3]\n" /* store envp into environ */
    -
    - "mov r4, r2\n" /* search for auxv (follows NULL after last env) */
    - "0:\n"
    - "mov r5, r4\n" /* r5 = r4 */
    - "add r4, r4, #4\n" /* r4 += 4 */
    - "ldr r5,[r5]\n" /* r5 = *r5 = *(r4-4) */
    - "cmp r5, #0\n" /* and stop at NULL after last env */
    - "bne 0b\n"
    - "ldr %r3, 2f\n" /* r3 = &_auxv (low bits) */
    - "str r4, [r3]\n" /* store r4 into _auxv */
    -
    - "mov %r3, $8\n" /* AAPCS : sp must be 8-byte aligned in the */
    - "neg %r3, %r3\n" /* callee, and bl doesn't push (lr=pc) */
    - "and %r3, %r3, %r1\n" /* so we do sp = r1(=sp) & r3(=-8); */
    - "mov %sp, %r3\n"
    -
    - "bl main\n" /* main() returns the status code, we'll exit with it. */
    - "movs r7, $1\n" /* NR_exit == 1 */
    - "svc $0x00\n"
    - ".align 2\n" /* below are the pointers to a few variables */
    - "1:\n"
    - ".word environ\n"
    - "2:\n"
    - ".word _auxv\n"
    + "mov %r0, sp\n" /* save stack pointer to %r0, as arg1 of _start_c */
    + "and ip, %r0, #-8\n" /* sp must be 8-byte aligned in the callee */
    + "mov sp, ip\n"
    + "bl _start_c\n" /* transfer to c runtime */
    );
    __builtin_unreachable();
    }
    --
    2.25.1
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