Re: [PATCH v3] Fix inferior memory reading in GDBServer for arm/aarch32

[Antoine Tremblay <antoine dot tremblay at ericsson dot com>]

Ping. (Sorry I had a mistake in Yao's email on 1st post)

Antoine Tremblay writes:

> In this v3:
>  * Stack reads are now done with ->read_memory
>  * Note tha this invalidated PATH 3/3 about sparc, since it's also a read from stack..
>  
> Before this patch, some functions would read the inferior memory with
> (*the_target)->read_memory, which returns the raw memory, rather than the
> shadowed memory.
>
> This is wrong since these functions do not expect to read a breakpoint
> instruction and can lead to invalid behavior.
>
> Use of raw memory in get_next_pcs_read_memory_unsigned_integer for example
> could lead to get_next_pc returning an invalid pc.
>
> Here's how this would happen:
>
> In non-stop:
>
> the user issues:
>
> thread 1
> step&
> thread 2
> step&
> thread 3
> step&
>
> In a similar way as non-stop-fair-events.exp (threads are looping).
>
> GDBServer:
>
>  linux_resume is called
>  GDBServer has pending events,
>  threads are not resumed and single-step breakpoint for thread 1 not installed.
>
>  linux_wait_1 is called with a pending event on thread 2 at pc A
>  GDBServer handles the event and calls proceed_all_lwps
>  This calls proceed_one_lwp and installs single-step breakpoints on all
>  the threads that need one.
>
>  Now since thread 1 needs to install a single-step breakpoint and is at pc B
>  (different than thread 2), a step-over is not initiated and get_next_pc
>  is called to figure out the next instruction from pc B.
>
>  However it may just be that thread 3 as a single step breakpoint at pc
>  B. And thus get_next_pc fails.
>
> This situation is tested with non-stop-fair-events.exp.
>
> In other words, single-step breakpoints are installed in proceed_one_lwp
> for each thread.  GDBserver proceeds two threads for resume_step, as
> requested by GDB, and the thread proceeded later may see the single-step
> breakpoints installed for the thread proceeded just now.
>
> Tested on gdbserver-native/-m{thumb,arm} no regressions.
>
> gdb/gdbserver/ChangeLog:
>
> 	* linux-aarch32-low.c (arm_breakpoint_kind_from_pc): Use
> 	target_read_memory.
> 	* linux-arm-low.c (get_next_pcs_read_memory_unsigned_integer): Likewise.
> 	(get_next_pcs_syscall_next_pc): Likewise.
> ---
>  gdb/gdbserver/linux-aarch32-low.c | 4 ++--
>  gdb/gdbserver/linux-arm-low.c     | 5 +++--
>  2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/gdb/gdbserver/linux-aarch32-low.c b/gdb/gdbserver/linux-aarch32-low.c
> index 5547cf6491..4ff34b626b 100644
> --- a/gdb/gdbserver/linux-aarch32-low.c
> +++ b/gdb/gdbserver/linux-aarch32-low.c
> @@ -237,11 +237,11 @@ arm_breakpoint_kind_from_pc (CORE_ADDR *pcptr)
>        *pcptr = UNMAKE_THUMB_ADDR (*pcptr);
>  
>        /* Check whether we are replacing a thumb2 32-bit instruction.  */
> -      if ((*the_target->read_memory) (*pcptr, buf, 2) == 0)
> +      if (target_read_memory (*pcptr, buf, 2) == 0)
>  	{
>  	  unsigned short inst1 = 0;
>  
> -	  (*the_target->read_memory) (*pcptr, (gdb_byte *) &inst1, 2);
> +	  target_read_memory (*pcptr, (gdb_byte *) &inst1, 2);
>  	  if (thumb_insn_size (inst1) == 4)
>  	    return ARM_BP_KIND_THUMB2;
>  	}
> diff --git a/gdb/gdbserver/linux-arm-low.c b/gdb/gdbserver/linux-arm-low.c
> index ed9b3562a8..930cc34f71 100644
> --- a/gdb/gdbserver/linux-arm-low.c
> +++ b/gdb/gdbserver/linux-arm-low.c
> @@ -263,7 +263,8 @@ get_next_pcs_read_memory_unsigned_integer (CORE_ADDR memaddr,
>    ULONGEST res;
>  
>    res = 0;
> -  (*the_target->read_memory) (memaddr, (unsigned char *) &res, len);
> +  target_read_memory (memaddr, (unsigned char *) &res, len);
> +
>    return res;
>  }
>  
> @@ -804,7 +805,7 @@ get_next_pcs_syscall_next_pc (struct arm_get_next_pcs *self)
>        unsigned long this_instr;
>        unsigned long svc_operand;
>  
> -      (*the_target->read_memory) (pc, (unsigned char *) &this_instr, 4);
> +      target_read_memory (pc, (unsigned char *) &this_instr, 4);
>        svc_operand = (0x00ffffff & this_instr);
>  
>        if (svc_operand)  /* OABI.  */