[Bug external/20207] New: kernel RFE: aarch64: ptrace: BAS: Support any contiguous range

["jan.kratochvil at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=20207

            Bug ID: 20207
           Summary: kernel RFE: aarch64: ptrace: BAS: Support any
                    contiguous range
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: external
          Assignee: unassigned at sourceware dot org
          Reporter: jan.kratochvil at redhat dot com
  Target Milestone: ---

A tracker for Linux kernel RFE:
https://bugzilla.redhat.com/show_bug.cgi?id=1342821

GDB currently misses some unaligned watchpoints.  GDB can be modified not to
miss then but then it will have some unaligned watchpoints false positives.
  Aarch64: watchpoints set on non-8-byte-aligned addresses are always missed
  https://sourceware.org/bugzilla/show_bug.cgi?id=19806
With this proposed kernel change GDB could be changed to support unaligned
watchpoints without misses and without false positives.

ARM Architecture Reference Manual ARMv8, for ARMv8-A architecture profile
The valid values for BAS are 0b0000000 , or a binary number all of whose set
bits are contiguous.

But current: linux-2.6/arch/arm64/kernel/hw_breakpoint.c
arch_bp_generic_fields()
permits only these 4 combinations:
#define ARM_BREAKPOINT_LEN_1    0x1
#define ARM_BREAKPOINT_LEN_2    0x3
#define ARM_BREAKPOINT_LEN_4    0xf
#define ARM_BREAKPOINT_LEN_8    0xff

Therefore Linux kernel should support arbitrary contiguous LEN value, not just
those 4 values above.

wget https://bugzilla.redhat.com/attachment.cgi?id=1164917;gcc -o
aarch64-watchpoint aarch64-watchpoint.c -Wall -g;./aarch64-watchpoint
./aarch64-watchpoint: PTRACE_SETREGSET: NT_ARM_HW_WATCH: Invalid argument

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