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

Antoine Tremblay antoine.tremblay@ericsson.com
Fri Dec 9 12:46:00 GMT 2016

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
thread 2
thread 3

In a similar way as non-stop-fair-events.exp (threads are looping).


 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.


	* linux-aarch32-low.c (arm_breakpoint_kind_from_pc): Use
	* 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.  */

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