gdb: add gdbarch_stack_grows_down function

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.

A new self-test ensures that all architectures have a stack that
either grows down, or grows up.

There should be no user visible changes after this commit.

Approved-By: Tom Tromey <tom@tromey.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
index 77d3406..d4c6795 100644
--- a/gdb/gdbarch.h
+++ b/gdb/gdbarch.h
@@ -370,4 +370,12 @@ 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)
+{
+  return gdbarch_inner_than (arch, 1, 2) != 0;
+}
+
 #endif