disassembly.txt

00001c50 <_ZN6pebble5usart26UsartInnerDebug.fmt..Write9write_str20h2ee4dcecc5128b1fkkaE>:
    1c50:       b580            push    {r7, lr}
    1c52:       b082            sub     sp, #8
    1c54:       e9cd 1200       strd    r1, r2, [sp]
    1c58:       4905            ldr     r1, [pc, #20]   ; (1c70 <_ZN6pebble5usart26UsartInnerDebug.fmt..Write9write_str20h2ee4dcecc5128b1fkkaE+0x20>)
    1c5a:       2001            movs    r0, #1
    1c5c:       2200            movs    r2, #0
    1c5e:       be00            bkpt    0x0000
    1c60:       4479            add     r1, pc
    1c62:       460b            mov     r3, r1
    1c64:       f000 fa92       bl      218c <app_log>
                        1c64: R_ARM_THM_CALL    app_log
    1c68:       2000            movs    r0, #0
    1c6a:       b002            add     sp, #8
    1c6c:       bd80            pop     {r7, pc}
    1c6e:       bf00            nop
    1c70:       000007b2        .word   0x000007b2
                        1c70: R_ARM_REL32       byte_str4284

gdb.txt

(gdb) disassemble $pc-0x10,+0x20
Dump of assembler code from 0x2001bef4 to 0x2001bf14:
   0x2001bef4:	push	{r7, lr}
   0x2001bef6:	sub	sp, #8
   0x2001bef8:	strd	r1, r2, [sp]
   0x2001befc:	ldr	r1, [pc, #20]	; (0x2001bf14)
   0x2001befe:	movs	r0, #1
   0x2001bf00:	movs	r2, #0
   0x2001bf02:	bkpt	0x0000
=> 0x2001bf04:	add	r1, pc
   0x2001bf06:	mov	r3, r1
   0x2001bf08:	bl	0x2001c430
   0x2001bf0c:	movs	r0, #0
   0x2001bf0e:	add	sp, #8
   0x2001bf10:	pop	{r7, pc}
   0x2001bf12:	nop
End of assembler dump.
(gdb) nexti
0x2001bf06 in ?? ()
(gdb) 
0x2001bf08 in ?? ()
(gdb) 
0x2001c430 in ?? ()
(gdb) disassemble $pc-0x10,+0x20
Dump of assembler code from 0x2001c420 to 0x2001c440:
   0x2001c420:	add	r1, pc
   0x2001c422:	bl	0x2001b870
   0x2001c426:	add	sp, #32
   0x2001c428:	pop	{r4, r5, r6, pc}
   0x2001c42a:	nop
   0x2001c42c:	lsls	r4, r6, #23
   0x2001c42e:	movs	r0, r0
=> 0x2001c430:	push	{r0, r1, r2, r3}
   0x2001c432:	ldr	r1, [pc, #4]	; (0x2001c438)
   0x2001c434:	b.w	0x2001a334
   0x2001c438:	lsls	r0, r1, #2
   0x2001c43a:	movs	r0, r0
   0x2001c43c:	push	{r0, r1, r2, r3}
   0x2001c43e:	ldr	r1, [pc, #4]	; (0x2001c444)
End of assembler dump.
(gdb) p/x *(unsigned int *)$sp@2
$40 = {0x6c6c6162, 0x73}
(gdb) nexti
0x2001c432 in ?? ()
(gdb) p/x *(unsigned int *)$sp@2
$41 = {0x1, 0x2001c6ba}
(gdb) p/x *(unsigned int *)$sp@6
$42 = {0x1, 0x2001c6ba, 0x0, 0x2001c6ba, 0x6c6c6162, 0x73}

impl.rs

pub struct UsartInnerDebug;

impl fmt::Write for UsartInnerDebug {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        unsafe { asm!("BKPT"); }
        unsafe { external::app_log(1, b"\0".as_ptr(), 0, b"\0".as_ptr(), s.as_ptr(), s.len()) };
        Ok(())
    }
}