[aarch64] Fix removal of non-address bits for PAuth

PR gdb/28947

The address_significant gdbarch setting was introduced as a way to remove
non-address bits from pointers, and it is specified by a constant.  This
constant represents the number of address bits in a pointer.

Right now AArch64 is the only architecture that uses it, and 56 was a
correct option so far.

But if we are using Pointer Authentication (PAuth), we might use up to 2 bytes
from the address space to store the required information.  We could also have
cases where we're using both PAuth and MTE.

We could adjust the constant to 48 to cover those cases, but this doesn't
cover the case where GDB needs to sign-extend kernel addresses after removal
of the non-address bits.

This has worked so far because bit 55 is used to select between kernel-space
and user-space addresses.  But trying to clear a range of bits crossing the
bit 55 boundary requires the hook to be smarter.

The following patch renames the gdbarch hook from significant_addr_bit to
remove_non_address_bits and passes a pointer as opposed to the number of
bits.  The hook is now responsible for removing the required non-address bits
and sign-extending the address if needed.

While at it, make GDB and GDBServer share some more code for aarch64 and add a
new arch-specific testcase gdb.arch/aarch64-non-address-bits.exp.

Bug-url: https://sourceware.org/bugzilla/show_bug.cgi?id=28947

Approved-By: Simon Marchi <simon.marchi@efficios.com>

1 files changed, 0 insertions, 22 deletions

diff --git a/gdb/utils.c b/gdb/utils.c
index 74917f2..4a715b9 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -3110,28 +3110,6 @@ show_debug_timestamp (struct ui_file *file, int from_tty,
 }
 
 
-/* See utils.h.  */
-
-CORE_ADDR
-address_significant (gdbarch *gdbarch, CORE_ADDR addr)
-{
-  /* Clear insignificant bits of a target address and sign extend resulting
-     address, avoiding shifts larger or equal than the width of a CORE_ADDR.
-     The local variable ADDR_BIT stops the compiler reporting a shift overflow
-     when it won't occur.  Skip updating of target address if current target
-     has not set gdbarch significant_addr_bit.  */
-  int addr_bit = gdbarch_significant_addr_bit (gdbarch);
-
-  if (addr_bit && (addr_bit < (sizeof (CORE_ADDR) * HOST_CHAR_BIT)))
-    {
-      CORE_ADDR sign = (CORE_ADDR) 1 << (addr_bit - 1);
-      addr &= ((CORE_ADDR) 1 << addr_bit) - 1;
-      addr = (addr ^ sign) - sign;
-    }
-
-  return addr;
-}
-
 const char *
 paddress (struct gdbarch *gdbarch, CORE_ADDR addr)
 {