* Re: Should a DW_OP_implicit_value be taken from the left end?
2016-12-21 21:39 ` Jan Kratochvil
@ 2016-12-23 18:18 ` Andreas Arnez
2017-01-01 20:13 ` Jan Kratochvil
0 siblings, 1 reply; 4+ messages in thread
From: Andreas Arnez @ 2016-12-23 18:18 UTC (permalink / raw)
To: Jan Kratochvil; +Cc: GDB Development, Tom Tromey
[-- Attachment #1: Type: text/plain, Size: 2213 bytes --]
Thanks for looking into this.
On Wed, Dec 21 2016, Jan Kratochvil wrote:
> When looking at the patch I think the patch may be wrong, I think the
> endianity should affect at least also the lines:
>
> case DWARF_VALUE_LITERAL:
> ...
> ldata = ctx.data + byte_offset;
> n -= byte_offset;
Right, that's another issue. If we revert the change for
DW_OP_implicit_value, it doesn't matter anymore, but the same bug occurs
with DW_OP_stack_value as well. I'll handle that separately.
> I really do not mind reverting the patch if you think so, that is up to the
> maintainers.
Note that I don't intend to revert the whole patch, only the part
affecting DW_OP_implicit_value (DWARF_VALUE_LITERAL).
> But when you ask me I miss here stating what the current GCC version does
> produce. Is GDB behavior fixed with current GCC by your proposed patch
> revert? If it breaks do you plan to change/fix also GCC? Does the GDB
> testsuite (particulerly the entryval testcases) have no regressions on s390*?
Right, the test suite has no regressions on s390*. And GCC can indeed
emit DWARF code that breaks with current GDB on s390x; and the proposed
patch would fix that. See attachment for an example.
> From my mail you reference I understand it as that my patch did fix some
> entryval testcases with GCC that time. Unfortunately the entryval testcases
> are provided as .S files prebuilt by GCC that time and they are difficult to
> reproduce with newer GCC as -O2 -g code changes too much with different GCC
> version, breaking various compiled code assumptions of the .exp file.
Your patch certainly fixed a real problem with DW_OP_stack_value, but I
doubt that the changes to the handling of DW_OP_implicit_value did. In
the patch description you stated:
"I am not completely sure with the DWARF standard understanding for
DW_OP_implicit_value (DWARF_VALUE_LITERAL) but I think it also should
be fixed (if such DWARF is valid at all)."
And Tom Tromey answered:
"I think I asked about this when implementing this DWARF addition in
gdb, but I can't find the messages right now."
Is there any any other information about the rationale of that change?
--
Andreas
[-- Attachment #2: implvalue.c --]
[-- Type: text/plain, Size: 603 bytes --]
/* DWARF test case that gets the compiler to emit DW_OP_implicit_value as
well as multiple instances of DW_OP_implicit_pointer, each pointing
into the implicit value with varying offsets. */
volatile int v;
static void
bar (char *a, char *b, char *c, char *d)
{
v = *a + *b + *c + *d;
}
int
main ()
{
__int128 u = (((__int128) 0x11223344556677 << 64) | 0x8899aabbccddeeff);
char *a = (char *) &u;
bar (a, a + 4, a + 8, a + 12);
/* Ensure that a location list is needed for u, so DW_AT_const_value can
not be used. */
u = ~u;
bar (a, a + 4, a + 8, a + 12);
return 0;
}
[-- Attachment #3: readelf -wio output --]
[-- Type: text/plain, Size: 6366 bytes --]
Contents of the .debug_info section:
Compilation Unit @ offset 0x0:
Length: 0x159 (32-bit)
Version: 4
Abbrev Offset: 0x0
Pointer Size: 8
<0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
<c> DW_AT_producer : (indirect string, offset: 0x21): GNU C11 7.0.0 20161222 (experimental) -march=zEC12 -mno-vx -mzarch -m64 -g -O3
<10> DW_AT_language : 12 (ANSI C99)
<11> DW_AT_name : (indirect string, offset: 0x10): implvalue.c
<15> DW_AT_comp_dir : (indirect string, offset: 0x0): /home/arnez/tmp
<19> DW_AT_ranges : 0x0
<1d> DW_AT_low_pc : 0x0
<25> DW_AT_stmt_list : 0x0
<1><29>: Abbrev Number: 2 (DW_TAG_variable)
<2a> DW_AT_name : v
<2c> DW_AT_decl_file : 1
<2d> DW_AT_decl_line : 5
<2e> DW_AT_type : <0x43>
<32> DW_AT_external : 1
<32> DW_AT_location : 9 byte block: 3 0 0 0 0 10 0 20 3c (DW_OP_addr: 1000203c)
<1><3c>: Abbrev Number: 3 (DW_TAG_base_type)
<3d> DW_AT_byte_size : 4
<3e> DW_AT_encoding : 5 (signed)
<3f> DW_AT_name : int
<1><43>: Abbrev Number: 4 (DW_TAG_volatile_type)
<44> DW_AT_type : <0x3c>
<1><48>: Abbrev Number: 5 (DW_TAG_subprogram)
<49> DW_AT_external : 1
<49> DW_AT_name : (indirect string, offset: 0x1c): main
<4d> DW_AT_decl_file : 1
<4e> DW_AT_decl_line : 14
<4f> DW_AT_type : <0x3c>
<53> DW_AT_low_pc : 0x10000418
<5b> DW_AT_high_pc : 0x18
<63> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa)
<65> DW_AT_GNU_all_call_sites: 1
<65> DW_AT_sibling : <0x11b>
<2><69>: Abbrev Number: 6 (DW_TAG_variable)
<6a> DW_AT_name : u
<6c> DW_AT_decl_file : 1
<6d> DW_AT_decl_line : 16
<6e> DW_AT_type : <0x11b>
<72> DW_AT_location : 0x0 (location list)
<2><76>: Abbrev Number: 7 (DW_TAG_variable)
<77> DW_AT_name : a
<79> DW_AT_decl_file : 1
<7a> DW_AT_decl_line : 17
<7b> DW_AT_type : <0x122>
<7f> DW_AT_location : 6 byte block: f2 0 0 0 69 0 (DW_OP_GNU_implicit_pointer: <0x69> 0)
<2><86>: Abbrev Number: 8 (DW_TAG_inlined_subroutine)
<87> DW_AT_abstract_origin: <0x12f>
<8b> DW_AT_low_pc : 0x10000418
<93> DW_AT_high_pc : 0xc
<9b> DW_AT_call_file : 1
<9c> DW_AT_call_line : 19
<9d> DW_AT_sibling : <0xd2>
<3><a1>: Abbrev Number: 9 (DW_TAG_formal_parameter)
<a2> DW_AT_abstract_origin: <0x137>
<a6> DW_AT_location : 6 byte block: f2 0 0 0 69 0 (DW_OP_GNU_implicit_pointer: <0x69> 0)
<3><ad>: Abbrev Number: 9 (DW_TAG_formal_parameter)
<ae> DW_AT_abstract_origin: <0x140>
<b2> DW_AT_location : 6 byte block: f2 0 0 0 69 4 (DW_OP_GNU_implicit_pointer: <0x69> 4)
<3><b9>: Abbrev Number: 9 (DW_TAG_formal_parameter)
<ba> DW_AT_abstract_origin: <0x149>
<be> DW_AT_location : 6 byte block: f2 0 0 0 69 8 (DW_OP_GNU_implicit_pointer: <0x69> 8)
<3><c5>: Abbrev Number: 9 (DW_TAG_formal_parameter)
<c6> DW_AT_abstract_origin: <0x152>
<ca> DW_AT_location : 6 byte block: f2 0 0 0 69 c (DW_OP_GNU_implicit_pointer: <0x69> 12)
<3><d1>: Abbrev Number: 0
<2><d2>: Abbrev Number: 10 (DW_TAG_inlined_subroutine)
<d3> DW_AT_abstract_origin: <0x12f>
<d7> DW_AT_low_pc : 0x10000424
<df> DW_AT_high_pc : 0x6
<e7> DW_AT_call_file : 1
<e8> DW_AT_call_line : 24
<3><e9>: Abbrev Number: 9 (DW_TAG_formal_parameter)
<ea> DW_AT_abstract_origin: <0x137>
<ee> DW_AT_location : 6 byte block: f2 0 0 0 69 0 (DW_OP_GNU_implicit_pointer: <0x69> 0)
<3><f5>: Abbrev Number: 9 (DW_TAG_formal_parameter)
<f6> DW_AT_abstract_origin: <0x140>
<fa> DW_AT_location : 6 byte block: f2 0 0 0 69 4 (DW_OP_GNU_implicit_pointer: <0x69> 4)
<3><101>: Abbrev Number: 9 (DW_TAG_formal_parameter)
<102> DW_AT_abstract_origin: <0x149>
<106> DW_AT_location : 6 byte block: f2 0 0 0 69 8 (DW_OP_GNU_implicit_pointer: <0x69> 8)
<3><10d>: Abbrev Number: 9 (DW_TAG_formal_parameter)
<10e> DW_AT_abstract_origin: <0x152>
<112> DW_AT_location : 6 byte block: f2 0 0 0 69 c (DW_OP_GNU_implicit_pointer: <0x69> 12)
<3><119>: Abbrev Number: 0
<2><11a>: Abbrev Number: 0
<1><11b>: Abbrev Number: 11 (DW_TAG_base_type)
<11c> DW_AT_byte_size : 16
<11d> DW_AT_encoding : 5 (signed)
<11e> DW_AT_name : (indirect string, offset: 0x70): __int128
<1><122>: Abbrev Number: 12 (DW_TAG_pointer_type)
<123> DW_AT_byte_size : 8
<124> DW_AT_type : <0x128>
<1><128>: Abbrev Number: 11 (DW_TAG_base_type)
<129> DW_AT_byte_size : 1
<12a> DW_AT_encoding : 8 (unsigned char)
<12b> DW_AT_name : (indirect string, offset: 0x79): char
<1><12f>: Abbrev Number: 13 (DW_TAG_subprogram)
<130> DW_AT_name : bar
<134> DW_AT_decl_file : 1
<135> DW_AT_decl_line : 8
<136> DW_AT_prototyped : 1
<136> DW_AT_inline : 1 (inlined)
<2><137>: Abbrev Number: 14 (DW_TAG_formal_parameter)
<138> DW_AT_name : a
<13a> DW_AT_decl_file : 1
<13b> DW_AT_decl_line : 8
<13c> DW_AT_type : <0x122>
<2><140>: Abbrev Number: 14 (DW_TAG_formal_parameter)
<141> DW_AT_name : b
<143> DW_AT_decl_file : 1
<144> DW_AT_decl_line : 8
<145> DW_AT_type : <0x122>
<2><149>: Abbrev Number: 14 (DW_TAG_formal_parameter)
<14a> DW_AT_name : c
<14c> DW_AT_decl_file : 1
<14d> DW_AT_decl_line : 8
<14e> DW_AT_type : <0x122>
<2><152>: Abbrev Number: 14 (DW_TAG_formal_parameter)
<153> DW_AT_name : d
<155> DW_AT_decl_file : 1
<156> DW_AT_decl_line : 8
<157> DW_AT_type : <0x122>
<2><15b>: Abbrev Number: 0
<1><15c>: Abbrev Number: 0
Contents of the .debug_loc section:
Offset Begin End Expression
00000000 0000000010000418 0000000010000424 (DW_OP_implicit_value 16 byte block: 0 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff )
00000024 0000000010000424 000000001000042a (DW_OP_implicit_value 16 byte block: ff ee dd cc bb aa 99 88 77 66 55 44 33 22 11 0 )
00000048 <End of list>
[-- Attachment #4: GDB session --]
[-- Type: text/plain, Size: 676 bytes --]
Reading symbols from implvalue...done.
(gdb) b main
Breakpoint 1 at 0x10000418: file implvalue.c, line 15.
(gdb) r
Starting program: /home/arnez/tmp/implvalue
Breakpoint 1, main () at implvalue.c:19
(gdb) si
0x000000001000041e in bar (a=<synthetic pointer>, b=<synthetic pointer>,
c=<synthetic pointer>, d=<synthetic pointer>) at implvalue.c:15
(gdb) p/x (char [4]) {*a, *b, *c, *d}
$1 = {0xff, 0xff, 0xff, 0xff}
(gdb) p/x *(char (*)[16]) a
$2 = {0x0, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd,
0xee, 0xff}
(gdb) p/x (char [8]) {a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7]}
$3 = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
^ permalink raw reply [flat|nested] 4+ messages in thread