Hi Janneke,

I get

gcc-mesboot.sh: line 20:  9438 Illegal instruction     (core dumped) ./a.out

│   0x276b8 <__writev+32>   svc     0x00000014                                 │
│  >0x276bc <__writev+36>   mov     r4, r0                                     │

The actual problem is at the first line above--the svc with argument != 0.

#0  0x000276bc in __writev (fd=2, vector=0xbebc54c0, count=10)
    at ../sysdeps/unix/sysv/linux/writev.c:51

glibc 2.2.5:sysdeps/unix/sysv/linux/writev.c:51

>  bytes_written = INLINE_SYSCALL (writev, 3, fd, CHECK_N (vector, count), count);

Err.... hmm?!

You *are* patching INLINE_SYSCALL body--so I'd guess that __ARM_EABI__ for
some reason is not being defined.

I'd suggest to #error (or at least #warning) if !__ARM_EABI__.