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

[jan.kratochvil at redhat dot com]

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

[jan.kratochvil at redhat dot com]

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

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |jan.kratochvil at redhat dot com,
| |palves at redhat dot com
Depends on| |19806


Referenced Bugs:

https://sourceware.org/bugzilla/show_bug.cgi?id=19806
[Bug 19806] Aarch64: watchpoints set on non-8-byte-aligned addresses are always
missed

[jan.kratochvil at redhat dot com]

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

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED

--- Comment #1 from Jan Kratochvil <jan.kratochvil at redhat dot com> ---
f43365ee17f8 selftests: arm64: add test for unaligned/inexact watchpoint
handling
0ddb8e0b784b arm64: Allow hw watchpoint of length 3,5,6 and 7
fdfeff0f9e3d arm64: hw_breakpoint: Handle inexact watchpoint addresses
b08fb180bb88 arm64: Allow hw watchpoint at varied offset from base address
651be3cb0853 hw_breakpoint: Allow watchpoint of length 3,5,6 and 7

[cvs-commit at gcc dot gnu.org]

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

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jan Kratochvil <***@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=a3b60e4588606354b93508a0008a5ca04b68fad8

commit a3b60e4588606354b93508a0008a5ca04b68fad8
Author: Jan Kratochvil <***@redhat.com>
Date: Fri May 4 22:22:04 2018 +0200

aarch64: PR 19806: watchpoints: false negatives + PR 20207 contiguous ones

Some unaligned watchpoints were currently missed.

On old kernels as specified in
kernel RFE: aarch64: ptrace: BAS: Support any contiguous range (edit)
https://sourceware.org/bugzilla/show_bug.cgi?id=20207
after this patch some other unaligned watchpoints will get reported as
false
positives.

With new kernels all the watchpoints should work exactly.

There may be a regresion that it now less merges watchpoints so that with
multiple overlapping watchpoints it may run out of the 4 hardware
watchpoint
registers. But as discussed in the original thread GDB needs some generic
watchpoints merging framework to be used by all the target specific code.
Even current FSF GDB code does not merge it perfectly. Also with the more
precise watchpoints one can technically merge them less. And I do not
think
it matters too much to improve mergeability only for old kernels.
Still even on new kernels some better merging logic would make sense.

There remains one issue:
kernel-4.15.14-300.fc27.armv7hl
FAIL: gdb.base/watchpoint-unaligned.exp: continue
FAIL: gdb.base/watchpoint-unaligned.exp: continue
(gdb) continue
Continuing.
Unexpected error setting watchpoint: Invalid argument.
(gdb) FAIL: gdb.base/watchpoint-unaligned.exp: continue
But that looks as a kernel bug to me.
(1) It is not a regression by this patch.
(2) It is unrelated to this patch.

gdb/ChangeLog
2018-05-04 Jan Kratochvil <***@redhat.com>
Pedro Alves <***@redhat.com>

PR breakpoints/19806 and support for PR external/20207.
* NEWS: Mention Aarch64 watchpoint improvements.
* aarch64-linux-nat.c (aarch64_linux_stopped_data_address): Fix missed
watchpoints and PR external/20207 watchpoints.
* nat/aarch64-linux-hw-point.c
(kernel_supports_any_contiguous_range): New.
(aarch64_watchpoint_offset): New.
(aarch64_watchpoint_length): Support PR external/20207 watchpoints.
(aarch64_point_encode_ctrl_reg): New parameter offset, new asserts.
(aarch64_point_is_aligned): Support PR external/20207 watchpoints.
(aarch64_align_watchpoint): New parameters aligned_offset_p and
next_addr_orig_p. Support PR external/20207 watchpoints.
(aarch64_downgrade_regs): New.
(aarch64_dr_state_insert_one_point): New parameters offset and
addr_orig.
(aarch64_dr_state_remove_one_point): Likewise.
(aarch64_handle_breakpoint): Update caller.
(aarch64_handle_aligned_watchpoint): Likewise.
(aarch64_handle_unaligned_watchpoint): Support addr_orig and
aligned_offset.
(aarch64_linux_set_debug_regs): Remove const from state. Call
aarch64_downgrade_regs.
(aarch64_show_debug_reg_state): Print also dr_addr_orig_wp.
* nat/aarch64-linux-hw-point.h (DR_CONTROL_LENGTH): Rename to ...
(DR_CONTROL_MASK): ... this.
(struct aarch64_debug_reg_state): New field dr_addr_orig_wp.
(unsigned int aarch64_watchpoint_offset): New prototype.
(aarch64_linux_set_debug_regs): Remove const from state.
* utils.c (align_up, align_down): Move to ...
* common/common-utils.c (align_up, align_down): ... here.
* utils.h (align_up, align_down): Move to ...
* common/common-utils.h (align_up, align_down): ... here.

gdb/gdbserver/ChangeLog
2018-05-04 Jan Kratochvil <***@redhat.com>
Pedro Alves <***@redhat.com>

* linux-aarch64-low.c (aarch64_stopped_data_address):
Likewise.

gdb/testsuite/ChangeLog
2018-05-04 Jan Kratochvil <***@redhat.com>
Pedro Alves <***@redhat.com>

PR breakpoints/19806 and support for PR external/20207.
* gdb.base/watchpoint-unaligned.c: New file.
* gdb.base/watchpoint-unaligned.exp: New file.

[jan.kratochvil at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20207
Bug 20207 depends on bug 19806, which changed state.

Bug 19806 Summary: Aarch64: watchpoints set on non-8-byte-aligned addresses are always missed
https://sourceware.org/bugzilla/show_bug.cgi?id=19806

What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED