[PATCH] gdb: add gdbarch_stack_grows_down function

[Andrew Burgess <aburgess@redhat.com>]

In another patch I'm working on I needed to ask: does the stack grow
down, or grow up?

Looking around I found in infcall.c some code where we needed to ask
the same question, what we do there is ask:

  gdbarch_inner_than (gdbarch, 1, 2)

which should do the job.  However, I don't particularly like copying
this, it feels like we're asking something slightly different that
just happens to align with the question we're actually asking.

I propose adding a new function `gdbarch_stack_grows_down`.  This is
not going to be a gdbarch method that can be overridden, instead, this
will just call the gdbarch_inner_than function.  We already have some
gdbarch methods like this, checkout arch-utils.c for examples.

I think it's now clearer what we're actually doing.

There should be no user visible changes after this commit.
---
 gdb/gdbarch.h | 13 +++++++++++++
 gdb/infcall.c | 10 ++++------
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
index 77d3406779f..70a6f43b06f 100644
--- a/gdb/gdbarch.h
+++ b/gdb/gdbarch.h
@@ -370,4 +370,17 @@ gdbarch_num_cooked_regs (gdbarch *arch)
   return gdbarch_num_regs (arch) + gdbarch_num_pseudo_regs (arch);
 }
 
+/* Return true if stacks for ARCH grow down, otherwise return true.  */
+
+static inline bool
+gdbarch_stack_grows_down (gdbarch *arch)
+{
+  /* The current assumption is that stacks either grow down, or they grow
+     up, so one of these checks should be true.  */
+  gdb_assert (gdbarch_inner_than (arch, 1, 2)
+	      || gdbarch_inner_than (arch, 2, 1));
+
+  return gdbarch_inner_than (arch, 1, 2);
+}
+
 #endif
diff --git a/gdb/infcall.c b/gdb/infcall.c
index 23d5652dd21..edac9a74179 100644
--- a/gdb/infcall.c
+++ b/gdb/infcall.c
@@ -947,7 +947,7 @@ reserve_stack_space (const type *values_type, CORE_ADDR &sp)
   struct gdbarch *gdbarch = get_frame_arch (frame);
   CORE_ADDR addr = 0;
 
-  if (gdbarch_inner_than (gdbarch, 1, 2))
+  if (gdbarch_stack_grows_down (gdbarch))
     {
       /* Stack grows downward.  Align STRUCT_ADDR and SP after
 	 making space.  */
@@ -1128,7 +1128,7 @@ call_function_by_hand_dummy (struct value *function,
 	   address.  AMD64 called that region the "red zone".  Skip at
 	   least the "red zone" size before allocating any space on
 	   the stack.  */
-	if (gdbarch_inner_than (gdbarch, 1, 2))
+	if (gdbarch_stack_grows_down (gdbarch))
 	  sp -= gdbarch_frame_red_zone_size (gdbarch);
 	else
 	  sp += gdbarch_frame_red_zone_size (gdbarch);
@@ -1156,11 +1156,9 @@ call_function_by_hand_dummy (struct value *function,
 	   to pay :-).  */
 	if (sp == old_sp)
 	  {
-	    if (gdbarch_inner_than (gdbarch, 1, 2))
-	      /* Stack grows down.  */
+	    if (gdbarch_stack_grows_down (gdbarch))
 	      sp = gdbarch_frame_align (gdbarch, old_sp - 1);
 	    else
-	      /* Stack grows up.  */
 	      sp = gdbarch_frame_align (gdbarch, old_sp + 1);
 	  }
 	/* SP may have underflown address zero here from OLD_SP.  Memory access
@@ -1193,7 +1191,7 @@ call_function_by_hand_dummy (struct value *function,
 	  {
 	    CORE_ADDR lastval_addr = lastval->address ();
 
-	    if (gdbarch_inner_than (gdbarch, 1, 2))
+	    if (gdbarch_stack_grows_down (gdbarch))
 	      {
 		gdb_assert (sp >= lastval_addr);
 		sp = lastval_addr;

base-commit: cba95c27876724059c3e99ea1857fb19b9cf8220
-- 
2.25.4