Re: ping: [patch] aarch64: PR 19806: watchpoints: false negatives + PR 20207 contiguous ones

[Jan Kratochvil <jan.kratochvil@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 4293 bytes --]

On Fri, 20 Apr 2018 16:49:39 +0200, Pedro Alves wrote:
> ~~~~~~~~~~~~
> Previously, when the hardware reported a watchpoint hit on an address
> that did not match our watchpoint (this happens in case of instructions
> which access large chunks of memory such as "stp") the process would
> enter a loop where we would be continually resuming it (because we did
> not recognise that watchpoint hit) and it would keep hitting the
> watchpoint again and again. The tracing process would never get
> notified of the watchpoint hit.
> ~~~~~~~~~~~~
> 
> ... I'm left with the impression that ADDR_TRAP could be even
> lower than addr_watch_aligned, in which case we'll still miss
> watchpoints.  I wondering whether GDB should be using a similar
> trick as that kernel patch does.

This is new for me what you found.  I just did not expect the changed region
region could be larger than aligned 8 bytes.

Unfortunately I cannot reproduce that so I cannot do much with that.
Does anyone know how to reproduce it?


Thanks,
Jan


I was unable to make GCC use the "stp" instruction so I hand-edited it there:
# gcc -o w2.S w2.c -Wall -g -O3 -S -dA
# output attached+edited
gcc -o w2 w2.S -Wall 

aarch64-7s-rhel-alt-v1.ss.eng.rdu.redhat.com
kernel-4.14.0-49.el7a.aarch64

../gdb -data-directory ../data-directory/ ./w2 -batch -ex 'b main' -ex r -ex 'p &g1' -ex 'p &g2' -ex 'b 8' -ex 'watch g2' -ex 'set debug infrun 1' -ex c -ex disas
Breakpoint 1 at 0x400458: file w2.c, line 7.
Breakpoint 1, main () at w2.c:7
7	  f(1,2);
$1 = (long *) 0x420030 <g1>
$2 = (long *) 0x420038 <g2>
Breakpoint 2 at 0x400464: file w2.c, line 9.
Hardware watchpoint 3: g2
infrun: clear_proceed_status_thread (process 30847)
infrun: proceed (addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT)
infrun: step-over queue now empty
infrun: resuming [process 30847] for step-over
infrun: resume (step=1, signal=GDB_SIGNAL_0), trap_expected=1, current thread [process 30847] at 0x400458
infrun: infrun_async(1)
infrun: prepare_to_wait
infrun: proceed: [process 30847] resumed
infrun: target_wait (-1.0.0, status) =
infrun:   30847.30847.0 [process 30847],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x40045c
infrun: no stepping, continue
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 30847] at 0x40045c
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun:   30847.30847.0 [process 30847],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x4005d8
infrun: stopped by watchpoint
infrun: stopped data address = 0x420038
infrun: stop_all_threads
infrun: stop_all_threads, pass=0, iterations=0
infrun:   process 30847 not executing
infrun: stop_all_threads, pass=1, iterations=1
infrun:   process 30847 not executing
infrun: stop_all_threads done
infrun: stepping past non-steppable watchpoint. skipping watchpoint at 0x420038:8
infrun: stepping past non-steppable watchpoint. skipping watchpoint at 0x420038:8
infrun: stepping past non-steppable watchpoint. skipping watchpoint at 0x420038:8
infrun: stepping past non-steppable watchpoint. skipping watchpoint at 0x420038:8
infrun: resume (step=1, signal=GDB_SIGNAL_0), trap_expected=1, current thread [process 30847] at 0x4005d8
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun:   30847.30847.0 [process 30847],
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
infrun: TARGET_WAITKIND_STOPPED
infrun: clear_step_over_info
infrun: restart threads: [process 30847] is event thread
infrun: stop_pc = 0x4005dc
infrun: BPSTAT_WHAT_STOP_NOISY
infrun: stop_waiting
infrun: stop_all_threads
infrun: stop_all_threads, pass=0, iterations=0
infrun:   process 30847 not executing
infrun: stop_all_threads, pass=1, iterations=1
infrun:   process 30847 not executing
infrun: stop_all_threads done
Hardware watchpoint 3: g2
Old value = 0
New value = 2
f (p1=p1@entry=1, p2=p2@entry=2) at w2.c:5
5	}
infrun: infrun_async(0)
Dump of assembler code for function f:
   0x00000000004005d0 <+0>:	adrp	x2, 0x420000 <__libc_start_main@got.plt>
   0x00000000004005d4 <+4>:	add	x2, x2, #0x30
   0x00000000004005d8 <+8>:	stp	x0, x1, [x2]
=> 0x00000000004005dc <+12>:	ret
End of assembler dump.

[-- Attachment #2: w2.S --]
[-- Type: text/plain, Size: 9977 bytes --]

	.cpu generic+fp+simd
	.file	"w2.c"
	.text
.Ltext0:
	.align	2
	.global	f
	.type	f, %function
f:
.LFB0:
	.file 1 "w2.c"
	// w2.c:2
	.loc 1 2 0
	.cfi_startproc
.LVL0:
// BLOCK 2 freq:10000 seq:0
// PRED: ENTRY [100.0%]  (FALLTHRU)
	// w2.c:3
	.loc 1 3 0
	adrp	x2, .LANCHOR0
	add	x2, x2, :lo12:.LANCHOR0
#if 0
	str	x0, [x2]
	// w2.c:4
	.loc 1 4 0
	str	x1, [x2,8]
#else
	stp	x0, x1, [x2]
#endif
// SUCC: EXIT [100.0%] 
	// w2.c:5
	.loc 1 5 0
	ret
	.cfi_endproc
.LFE0:
	.size	f, .-f
	.section	.text.startup,"ax",%progbits
	.align	2
	.global	main
	.type	main, %function
main:
.LFB1:
	// w2.c:6
	.loc 1 6 0
	.cfi_startproc
// BLOCK 2 freq:10000 seq:0
// PRED: ENTRY [100.0%]  (FALLTHRU)
	stp	x29, x30, [sp, -16]!
	.cfi_def_cfa_offset 16
	.cfi_offset 29, -16
	.cfi_offset 30, -8
	add	x29, sp, 0
	.cfi_def_cfa_register 29
	// w2.c:7
	.loc 1 7 0
	mov	x0, 1
	mov	x1, 2
	bl	f
.LVL1:
	// w2.c:9
	.loc 1 9 0
	mov	w0, 0
	ldp	x29, x30, [sp], 16
	.cfi_restore 30
	.cfi_restore 29
	.cfi_def_cfa 31, 0
// SUCC: EXIT [100.0%] 
	ret
	.cfi_endproc
.LFE1:
	.size	main, .-main
	.bss
	.align	3
	.zero	8
.LANCHOR0 = . + 0
	.type	g1, %object
	.size	g1, 8
g1:
	.zero	8
	.type	g2, %object
	.size	g2, 8
g2:
	.zero	8
	.text
.Letext0:
	.section	.debug_info,"",%progbits
.Ldebug_info0:
	.4byte	0xca	// Length of Compilation Unit Info
	.2byte	0x4	// DWARF version number
	.4byte	.Ldebug_abbrev0	// Offset Into Abbrev. Section
	.byte	0x8	// Pointer Size (in bytes)
	.uleb128 0x1	// (DIE (0xb) DW_TAG_compile_unit)
	.4byte	.LASF1	// DW_AT_producer: "GNU C 4.8.5 20150623 (Red Hat 4.8.5-28) -g -O3"
	.byte	0x1	// DW_AT_language
	.4byte	.LASF2	// DW_AT_name: "w2.c"
	.4byte	.LASF3	// DW_AT_comp_dir: "/root/jkratoch/redhat/gdb-git/gdb/testsuite"
	.4byte	.Ldebug_ranges0+0	// DW_AT_ranges
	.8byte	0	// DW_AT_low_pc
	.4byte	.Ldebug_line0	// DW_AT_stmt_list
	.uleb128 0x2	// (DIE (0x29) DW_TAG_subprogram)
			// DW_AT_external
	.ascii "f\0"	// DW_AT_name
	.byte	0x1	// DW_AT_decl_file (w2.c)
	.byte	0x2	// DW_AT_decl_line
			// DW_AT_prototyped
	.8byte	.LFB0	// DW_AT_low_pc
	.8byte	.LFE0-.LFB0	// DW_AT_high_pc
	.uleb128 0x1	// DW_AT_frame_base
	.byte	0x9c	// DW_OP_call_frame_cfa
			// DW_AT_GNU_all_call_sites
	.4byte	0x5d	// DW_AT_sibling
	.uleb128 0x3	// (DIE (0x44) DW_TAG_formal_parameter)
	.ascii "p1\0"	// DW_AT_name
	.byte	0x1	// DW_AT_decl_file (w2.c)
	.byte	0x2	// DW_AT_decl_line
	.4byte	0x5d	// DW_AT_type
	.uleb128 0x1	// DW_AT_location
	.byte	0x50	// DW_OP_reg0
	.uleb128 0x3	// (DIE (0x50) DW_TAG_formal_parameter)
	.ascii "p2\0"	// DW_AT_name
	.byte	0x1	// DW_AT_decl_file (w2.c)
	.byte	0x2	// DW_AT_decl_line
	.4byte	0x5d	// DW_AT_type
	.uleb128 0x1	// DW_AT_location
	.byte	0x51	// DW_OP_reg1
	.byte	0	// end of children of DIE 0x29
	.uleb128 0x4	// (DIE (0x5d) DW_TAG_base_type)
	.byte	0x8	// DW_AT_byte_size
	.byte	0x5	// DW_AT_encoding
	.4byte	.LASF0	// DW_AT_name: "long int"
	.uleb128 0x5	// (DIE (0x64) DW_TAG_subprogram)
			// DW_AT_external
	.4byte	.LASF4	// DW_AT_name: "main"
	.byte	0x1	// DW_AT_decl_file (w2.c)
	.byte	0x6	// DW_AT_decl_line
			// DW_AT_prototyped
	.4byte	0x9e	// DW_AT_type
	.8byte	.LFB1	// DW_AT_low_pc
	.8byte	.LFE1-.LFB1	// DW_AT_high_pc
	.uleb128 0x1	// DW_AT_frame_base
	.byte	0x9c	// DW_OP_call_frame_cfa
			// DW_AT_GNU_all_call_sites
	.4byte	0x9e	// DW_AT_sibling
	.uleb128 0x6	// (DIE (0x85) DW_TAG_GNU_call_site)
	.8byte	.LVL1	// DW_AT_low_pc
	.4byte	0x29	// DW_AT_abstract_origin
	.uleb128 0x7	// (DIE (0x92) DW_TAG_GNU_call_site_parameter)
	.uleb128 0x1	// DW_AT_location
	.byte	0x51	// DW_OP_reg1
	.uleb128 0x1	// DW_AT_GNU_call_site_value
	.byte	0x32	// DW_OP_lit2
	.uleb128 0x7	// (DIE (0x97) DW_TAG_GNU_call_site_parameter)
	.uleb128 0x1	// DW_AT_location
	.byte	0x50	// DW_OP_reg0
	.uleb128 0x1	// DW_AT_GNU_call_site_value
	.byte	0x31	// DW_OP_lit1
	.byte	0	// end of children of DIE 0x85
	.byte	0	// end of children of DIE 0x64
	.uleb128 0x8	// (DIE (0x9e) DW_TAG_base_type)
	.byte	0x4	// DW_AT_byte_size
	.byte	0x5	// DW_AT_encoding
	.ascii "int\0"	// DW_AT_name
	.uleb128 0x9	// (DIE (0xa5) DW_TAG_variable)
	.ascii "g1\0"	// DW_AT_name
	.byte	0x1	// DW_AT_decl_file (w2.c)
	.byte	0x1	// DW_AT_decl_line
	.4byte	0x5d	// DW_AT_type
	.uleb128 0x9	// DW_AT_location
	.byte	0x3	// DW_OP_addr
	.8byte	g1
	.uleb128 0x9	// (DIE (0xb9) DW_TAG_variable)
	.ascii "g2\0"	// DW_AT_name
	.byte	0x1	// DW_AT_decl_file (w2.c)
	.byte	0x1	// DW_AT_decl_line
	.4byte	0x5d	// DW_AT_type
	.uleb128 0x9	// DW_AT_location
	.byte	0x3	// DW_OP_addr
	.8byte	g2
	.byte	0	// end of children of DIE 0xb
	.section	.debug_abbrev,"",%progbits
.Ldebug_abbrev0:
	.uleb128 0x1	// (abbrev code)
	.uleb128 0x11	// (TAG: DW_TAG_compile_unit)
	.byte	0x1	// DW_children_yes
	.uleb128 0x25	// (DW_AT_producer)
	.uleb128 0xe	// (DW_FORM_strp)
	.uleb128 0x13	// (DW_AT_language)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x3	// (DW_AT_name)
	.uleb128 0xe	// (DW_FORM_strp)
	.uleb128 0x1b	// (DW_AT_comp_dir)
	.uleb128 0xe	// (DW_FORM_strp)
	.uleb128 0x55	// (DW_AT_ranges)
	.uleb128 0x17	// (DW_FORM_sec_offset)
	.uleb128 0x11	// (DW_AT_low_pc)
	.uleb128 0x1	// (DW_FORM_addr)
	.uleb128 0x10	// (DW_AT_stmt_list)
	.uleb128 0x17	// (DW_FORM_sec_offset)
	.byte	0
	.byte	0
	.uleb128 0x2	// (abbrev code)
	.uleb128 0x2e	// (TAG: DW_TAG_subprogram)
	.byte	0x1	// DW_children_yes
	.uleb128 0x3f	// (DW_AT_external)
	.uleb128 0x19	// (DW_FORM_flag_present)
	.uleb128 0x3	// (DW_AT_name)
	.uleb128 0x8	// (DW_FORM_string)
	.uleb128 0x3a	// (DW_AT_decl_file)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x3b	// (DW_AT_decl_line)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x27	// (DW_AT_prototyped)
	.uleb128 0x19	// (DW_FORM_flag_present)
	.uleb128 0x11	// (DW_AT_low_pc)
	.uleb128 0x1	// (DW_FORM_addr)
	.uleb128 0x12	// (DW_AT_high_pc)
	.uleb128 0x7	// (DW_FORM_data8)
	.uleb128 0x40	// (DW_AT_frame_base)
	.uleb128 0x18	// (DW_FORM_exprloc)
	.uleb128 0x2117	// (DW_AT_GNU_all_call_sites)
	.uleb128 0x19	// (DW_FORM_flag_present)
	.uleb128 0x1	// (DW_AT_sibling)
	.uleb128 0x13	// (DW_FORM_ref4)
	.byte	0
	.byte	0
	.uleb128 0x3	// (abbrev code)
	.uleb128 0x5	// (TAG: DW_TAG_formal_parameter)
	.byte	0	// DW_children_no
	.uleb128 0x3	// (DW_AT_name)
	.uleb128 0x8	// (DW_FORM_string)
	.uleb128 0x3a	// (DW_AT_decl_file)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x3b	// (DW_AT_decl_line)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x49	// (DW_AT_type)
	.uleb128 0x13	// (DW_FORM_ref4)
	.uleb128 0x2	// (DW_AT_location)
	.uleb128 0x18	// (DW_FORM_exprloc)
	.byte	0
	.byte	0
	.uleb128 0x4	// (abbrev code)
	.uleb128 0x24	// (TAG: DW_TAG_base_type)
	.byte	0	// DW_children_no
	.uleb128 0xb	// (DW_AT_byte_size)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x3e	// (DW_AT_encoding)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x3	// (DW_AT_name)
	.uleb128 0xe	// (DW_FORM_strp)
	.byte	0
	.byte	0
	.uleb128 0x5	// (abbrev code)
	.uleb128 0x2e	// (TAG: DW_TAG_subprogram)
	.byte	0x1	// DW_children_yes
	.uleb128 0x3f	// (DW_AT_external)
	.uleb128 0x19	// (DW_FORM_flag_present)
	.uleb128 0x3	// (DW_AT_name)
	.uleb128 0xe	// (DW_FORM_strp)
	.uleb128 0x3a	// (DW_AT_decl_file)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x3b	// (DW_AT_decl_line)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x27	// (DW_AT_prototyped)
	.uleb128 0x19	// (DW_FORM_flag_present)
	.uleb128 0x49	// (DW_AT_type)
	.uleb128 0x13	// (DW_FORM_ref4)
	.uleb128 0x11	// (DW_AT_low_pc)
	.uleb128 0x1	// (DW_FORM_addr)
	.uleb128 0x12	// (DW_AT_high_pc)
	.uleb128 0x7	// (DW_FORM_data8)
	.uleb128 0x40	// (DW_AT_frame_base)
	.uleb128 0x18	// (DW_FORM_exprloc)
	.uleb128 0x2117	// (DW_AT_GNU_all_call_sites)
	.uleb128 0x19	// (DW_FORM_flag_present)
	.uleb128 0x1	// (DW_AT_sibling)
	.uleb128 0x13	// (DW_FORM_ref4)
	.byte	0
	.byte	0
	.uleb128 0x6	// (abbrev code)
	.uleb128 0x4109	// (TAG: DW_TAG_GNU_call_site)
	.byte	0x1	// DW_children_yes
	.uleb128 0x11	// (DW_AT_low_pc)
	.uleb128 0x1	// (DW_FORM_addr)
	.uleb128 0x31	// (DW_AT_abstract_origin)
	.uleb128 0x13	// (DW_FORM_ref4)
	.byte	0
	.byte	0
	.uleb128 0x7	// (abbrev code)
	.uleb128 0x410a	// (TAG: DW_TAG_GNU_call_site_parameter)
	.byte	0	// DW_children_no
	.uleb128 0x2	// (DW_AT_location)
	.uleb128 0x18	// (DW_FORM_exprloc)
	.uleb128 0x2111	// (DW_AT_GNU_call_site_value)
	.uleb128 0x18	// (DW_FORM_exprloc)
	.byte	0
	.byte	0
	.uleb128 0x8	// (abbrev code)
	.uleb128 0x24	// (TAG: DW_TAG_base_type)
	.byte	0	// DW_children_no
	.uleb128 0xb	// (DW_AT_byte_size)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x3e	// (DW_AT_encoding)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x3	// (DW_AT_name)
	.uleb128 0x8	// (DW_FORM_string)
	.byte	0
	.byte	0
	.uleb128 0x9	// (abbrev code)
	.uleb128 0x34	// (TAG: DW_TAG_variable)
	.byte	0	// DW_children_no
	.uleb128 0x3	// (DW_AT_name)
	.uleb128 0x8	// (DW_FORM_string)
	.uleb128 0x3a	// (DW_AT_decl_file)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x3b	// (DW_AT_decl_line)
	.uleb128 0xb	// (DW_FORM_data1)
	.uleb128 0x49	// (DW_AT_type)
	.uleb128 0x13	// (DW_FORM_ref4)
	.uleb128 0x2	// (DW_AT_location)
	.uleb128 0x18	// (DW_FORM_exprloc)
	.byte	0
	.byte	0
	.byte	0
	.section	.debug_aranges,"",%progbits
	.4byte	0x3c	// Length of Address Ranges Info
	.2byte	0x2	// DWARF Version
	.4byte	.Ldebug_info0	// Offset of Compilation Unit Info
	.byte	0x8	// Size of Address
	.byte	0	// Size of Segment Descriptor
	.2byte	0	// Pad to 16 byte boundary
	.2byte	0
	.8byte	.Ltext0	// Address
	.8byte	.Letext0-.Ltext0	// Length
	.8byte	.LFB1	// Address
	.8byte	.LFE1-.LFB1	// Length
	.8byte	0
	.8byte	0
	.section	.debug_ranges,"",%progbits
.Ldebug_ranges0:
	.8byte	.Ltext0	// Offset 0
	.8byte	.Letext0
	.8byte	.LFB1	// Offset 0x10
	.8byte	.LFE1
	.8byte	0
	.8byte	0
	.section	.debug_line,"",%progbits
.Ldebug_line0:
	.section	.debug_str,"MS",%progbits,1
.LASF3:
	.string	"/root/jkratoch/redhat/gdb-git/gdb/testsuite"
.LASF2:
	.string	"w2.c"
.LASF0:
	.string	"long int"
.LASF4:
	.string	"main"
.LASF1:
	.string	"GNU C 4.8.5 20150623 (Red Hat 4.8.5-28) -g -O3"
	.ident	"GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-28)"
	.section	.note.GNU-stack,"",%progbits