gdbserver: allows agent_mem_read to return an error code

Currently the gdbserver function agent_mem_read ignores any errors
from calling read_inferior_memory.  This means that if there is an
attempt to access invalid memory then this will appear to succeed.

In this patch I update agent_mem_read so that if read_inferior_memory
fails, agent_mem_read will return an error code.

However, none of the callers of agent_mem_read actually check the
return value, so this commit will have no effect on anything.  In the
next commit I will update the users of agent_mem_read to check for the
error code.

I've also updated the header comments on agent_mem_read to better
reflect what the function does, and its possible return values.

1 files changed, 7 insertions, 2 deletions

diff --git a/gdbserver/tracepoint.h b/gdbserver/tracepoint.h
index 060d44d..1f40d7b 100644
--- a/gdbserver/tracepoint.h
+++ b/gdbserver/tracepoint.h
@@ -161,8 +161,13 @@ void gdb_agent_about_to_close (int pid);
 struct traceframe;
 struct eval_agent_expr_context;
 
-/* Do memory copies for bytecodes.  */
-/* Do the recording of memory blocks for actions and bytecodes.  */
+/* When TO is not NULL, do memory copies for bytecodes, read LEN bytes
+   starting at address FROM, and place the result in the buffer TO.
+   Return 0 on success, otherwise a non-zero error code.
+
+   When TO is NULL, do the recording of memory blocks for actions and
+   bytecodes into a new traceframe block.  Return 0 on success, otherwise,
+   return 1 if there is an error.  */
 
 int agent_mem_read (struct eval_agent_expr_context *ctx,
 		    unsigned char *to, CORE_ADDR from,