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Date: Wed, 13 Nov 2013 06:48:00 -0000
Message-ID: <CAJOr74hUMywBACxchzpsL=+bur4s=iJaVQNdU0T0S4M2X15idw@mail.gmail.com>
Subject: Re: back into the thread....
From: Phi Debian <phi.debian@gmail.com>
To: Sterling Augustine <saugustine@google.com>
Cc: Mark Manning <mark4th@gmail.com>, gdb@sourceware.org
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Hi All,

Off topic about gdb discution

>  if (posix_memalign((void **) &dst, 4096*8, EXEC_BYTES) != 0) {
>   printf("can't allocate.\n");
>  exit (-1);
>  }
>  if (mprotect(dst, EXEC_BYTES, PROT_READ|PROT_WRITE|PROT_EXEC) != 0) {
>    printf("can't mprotect\n");
>    exit (-1);
>  }

>   memcpy(dst, bytes, EXEC_BYTES);
>
>   return_val = dst(test_val);


The above code as very little chance to execute on modernn
architecture, at least with architecture with separate icache and
dcache.

The memcpy fill the dcache, the dst() read the icache, since the
caches are not flushed in between, the dst() will execute garbage
(well instruction living there before).

As far as GDB is concerned, it should be able to single step in any
memory area that is declared 'executable'

> Also, the "can not access addres zero" error is totally bogus,
Not if you consider your single step execute garbage instruction.


Cheers,
Phi