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
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
The master branch has been updated by Jan Kratochvil <jkratoch@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=a3b60e4588606354b93508a0008a5ca04b68fad8 commit a3b60e4588606354b93508a0008a5ca04b68fad8 Author: Jan Kratochvil <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 <jan.kratochvil@redhat.com> Pedro Alves <palves@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 <jan.kratochvil@redhat.com> Pedro Alves <palves@redhat.com> * linux-aarch64-low.c (aarch64_stopped_data_address): Likewise. gdb/testsuite/ChangeLog 2018-05-04 Jan Kratochvil <jan.kratochvil@redhat.com> Pedro Alves <palves@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.