[PATCH v2] Fix inferior memory reading in GDBServer for arm/aarch32

[Antoine Tremblay <antoine.tremblay@ericsson.com>]

In this v2:
 * Added more explainations to the commit log

Yao are you ok with the changes in the other functions too ? (for good practice ? )
I could make it another patch for them too... not sure.

-
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.
	(arm_sigreturn_next_pc): Likewise.
	(get_next_pcs_syscall_next_pc): Likewise.
	(arm_get_syscall_trapinfo): Likewise.
---
 gdb/gdbserver/linux-aarch32-low.c |  4 ++--
 gdb/gdbserver/linux-arm-low.c     | 13 +++++++------
 2 files changed, 9 insertions(+), 8 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..b8365cf0b9 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;
 }
 
@@ -769,15 +770,15 @@ arm_sigreturn_next_pc (struct regcache *regcache, int svc_number,
   gdb_assert (svc_number == __NR_sigreturn || svc_number == __NR_rt_sigreturn);
 
   collect_register_by_name (regcache, "sp", &sp);
-  (*the_target->read_memory) (sp, (unsigned char *) &sp_data, 4);
+  target_read_memory (sp, (unsigned char *) &sp_data, 4);
 
   pc_offset = arm_linux_sigreturn_next_pc_offset
     (sp, sp_data, svc_number, __NR_sigreturn == svc_number ? 1 : 0);
 
-  (*the_target->read_memory) (sp + pc_offset, (unsigned char *) &next_pc, 4);
+  target_read_memory (sp + pc_offset, (unsigned char *) &next_pc, 4);
 
   /* Set IS_THUMB according the CPSR saved on the stack.  */
-  (*the_target->read_memory) (sp + pc_offset + 4, (unsigned char *) &cpsr, 4);
+  target_read_memory (sp + pc_offset + 4, (unsigned char *) &cpsr, 4);
   *is_thumb = ((cpsr & CPSR_T) != 0);
 
   return next_pc;
@@ -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.  */
@@ -965,7 +966,7 @@ arm_get_syscall_trapinfo (struct regcache *regcache, int *sysno)
 
       collect_register_by_name (regcache, "pc", &pc);
 
-      if ((*the_target->read_memory) (pc - 4, (unsigned char *) &insn, 4))
+      if (target_read_memory (pc - 4, (unsigned char *) &insn, 4))
 	*sysno = UNKNOWN_SYSCALL;
       else
 	{
-- 
2.11.0