thr3ads.net - llvm dev - [llvm-dev] Debug info scope of explicit casting type does not seem correct [May 2016]

If this information is useful, please help other people find it:
Share via:

Aboud, Amjad via llvm-dev

2016-Apr-30 10:32 UTC

[llvm-dev] Debug info scope of explicit casting type does not seem correct

Hi,
I am wondering if this behavior of creating debug info is correct.
A type in compile unit entry is pointing to a type under subprogram entry?!

This is the root cause of https://llvm.org/bugs/show_bug.cgi?id=27579

0x0000000b: DW_TAG_compile_unit [1] *

0x00000026:   DW_TAG_pointer_type [2]
                            DW_AT_type [DW_FORM_ref4]       (cu + 0x002c =>
{0x0000002c})

0x0000002b:   DW_TAG_subprogram [3] *

0x0000002c:     DW_TAG_typedef [4]
                               DW_AT_type [DW_FORM_ref4]     (cu + 0x0040 =>
{0x00000040})
                               DW_AT_name [DW_FORM_strp]     (
.debug_str[0x00000060] = "T")
                               DW_AT_decl_file [DW_FORM_data1]      
("c:\temp\ICL\LB\retain.cpp")
                               DW_AT_decl_line [DW_FORM_data1]       (16)

0x00000037:     NULL


command line:
clang -cc1 -triple i386-apple-ios9.0.0 -emit-obj -debug-info-kind=limited -O2
test.cpp -o - | llvm-dwarfdump -debug-dump=info -
> cat test.cppclass A {
public:
  int x;
};


class B {
public:
  typedef A type;
};

template<typename X>
int foo(void* in) {
  typedef typename X::type T;
  const T* p = (T*) in;
  return p->x;
}

int bar() {
A a;
  return foo<B>(&a);
}

Reason for this behavior is the explicit cast "(T*)", which leads into
the following IR:

!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer:
"clang version 3.9.0 (trunk 267335)", isOptimized: true,
runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3)
!3 = !{!4}
!4 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !5, size: 32, align: 32)
<----------------- No Scope, leads to compile unit scope!!
!5 = !DIDerivedType(tag: DW_TAG_typedef, name: "T", scope: !7, file:
!6, line: 16, baseType: !20)
!7 = distinct !DISubprogram(name: "foo<B>", linkageName:
"_Z3fooI1BEiPv", scope: !6, file: !6, line: 15, type: !8, isLocal:
false, isDefinition: true, scopeLine: 15, flags: DIFlagPrototyped, isOptimized:
true, unit: !0, templateParams: !12, variables: !15)


Thanks,
Amjad

---------------------------------------------------------------------
Intel Israel (74) Limited

This e-mail and any attachments may contain confidential material for
the sole use of the intended recipient(s). Any review or distribution
by others is strictly prohibited. If you are not the intended
recipient, please contact the sender and delete all copies.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20160430/36162ab0/attachment.html>

David Blaikie via llvm-dev

2016-Apr-30 14:58 UTC

head link

[llvm-dev] Debug info scope of explicit casting type does not seem correct

Yep, seems fine/reasonable to me. The pointer type has no logical scope so
it doesn't really matter where its DIE goes.

GCC does put the pointer type in the function scope in basic cases, but it
can also end up in other places. For example:

blaikie at blaikie-linux:~/dev$ cat func.cpp
void sink(void*);
template<typename T>
void f1() {
  T *t;
  sink(&t);
}
void f2() {
  struct foo { };
  f1<foo>();
}
blaikie at blaikie-linux:~/dev$ g++-4.7 -std=c++11 func.cpp -g -c &&
llvm-dwarfdump-tot -debug-dump=info func.o | grep DW_TAG
0x0000000b: DW_TAG_compile_unit [1] *
0x0000002d:   DW_TAG_subprogram [2] * // f2
0x00000051:     DW_TAG_lexical_block [3]
0x00000062:     DW_TAG_structure_type [4]
0x0000006b:   DW_TAG_subprogram [5] * // f1
0x00000087:     DW_TAG_template_type_parameter [6]
0x0000008e:     DW_TAG_lexical_block [7] *
0x0000009f:       DW_TAG_variable [8]
0x000000ab:       DW_TAG_pointer_type [9]  // foo*

& in fact, if you introduce another template that's similar to f1, its
variable's type is 0x00ab - so it points into f1's children. Seems GCC
puts it in whatever scope first references the pointer type.

I think it's probably as sensible, and a bit simpler, to put any such
basic types in the CU scope.

(granted, if GCC and Clang were really smart, the pointer type in f1
could be pointer to 0x0087 - but that would really bloat the debug
info (now every different way of writing foo* in every different
template would be a separate type description... - that would probably
be not good))


On Sat, Apr 30, 2016 at 3:32 AM, Aboud, Amjad <amjad.aboud at intel.com>
wrote:
> Hi,
>
> I am wondering if this behavior of creating debug info is correct.
>
> A type in compile unit entry is pointing to a type under subprogram entry?!
>
>
>
> This is the root cause of https://llvm.org/bugs/show_bug.cgi?id=27579
>
>
>
> 0x0000000b: DW_TAG_compile_unit [1] *
>
>
>
> 0x00000026:   DW_TAG_pointer_type [2]
>
>                             DW_AT_type [DW_FORM_ref4]       (cu + 0x002c
> => {0x0000002c})
>
>
>
> 0x0000002b:   DW_TAG_subprogram [3] *
>
>
>
> 0x0000002c:     DW_TAG_typedef [4]
>
>                                DW_AT_type [DW_FORM_ref4]     (cu + 0x0040
> => {0x00000040})
>
>                                DW_AT_name [DW_FORM_strp]     (
> .debug_str[0x00000060] = "T")
>
>                                DW_AT_decl_file [DW_FORM_data1]
> ("c:\temp\ICL\LB\retain.cpp")
>
>                                DW_AT_decl_line [DW_FORM_data1]       (16)
>
>
>
> 0x00000037:     NULL
>
>
>
>
>
> command line:
>
> clang -cc1 -triple i386-apple-ios9.0.0 -emit-obj -debug-info-kind=limited
> -O2 test.cpp –o - | llvm-dwarfdump -debug-dump=info -
>
>
>
> > cat test.cpp
>
> class A {
>
> public:
>
>   int x;
>
> };
>
>
>
>
>
> class B {
>
> public:
>
>   typedef A type;
>
> };
>
>
>
> template<typename X>
>
> int foo(void* in) {
>
>   typedef typename X::type T;
>
>   const T* p = (T*) in;
>
>   return p->x;
>
> }
>
>
>
> int bar() {
>
> A a;
>
>   return foo<B>(&a);
>
> }
>
>
>
> Reason for this behavior is the explicit cast “(T*)“, which leads into the
> following IR:
>
>
>
> !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1,
> producer: "clang version 3.9.0 (trunk 267335)", isOptimized:
true,
> runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3)
>
> !3 = !{!4}
>
> !4 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !5, size: 32,
> align: 32)  <----------------- No Scope, leads to compile unit scope!!
>
> !5 = !DIDerivedType(tag: DW_TAG_typedef, name: "T", scope: !7,
file: !6,
> line: 16, baseType: !20)
>
> !7 = distinct !DISubprogram(name: "foo<B>", linkageName:
"_Z3fooI1BEiPv",
> scope: !6, file: !6, line: 15, type: !8, isLocal: false, isDefinition:
> true, scopeLine: 15, flags: DIFlagPrototyped, isOptimized: true, unit: !0,
> templateParams: !12, variables: !15)
>
>
>
>
>
> Thanks,
>
> Amjad
>
>
>
> ---------------------------------------------------------------------
> Intel Israel (74) Limited
>
> This e-mail and any attachments may contain confidential material for
> the sole use of the intended recipient(s). Any review or distribution
> by others is strictly prohibited. If you are not the intended
> recipient, please contact the sender and delete all copies.
>-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20160430/621d4f8e/attachment.html>

Aboud, Amjad via llvm-dev

2016-May-07 10:02 UTC

head link

[llvm-dev] Debug info scope of explicit casting type does not seem correct

Hi David,
OK, I got that DIE in Compile Unit scope may point to a DIE in subprogram scope.
But how about that we are emitting a subprogram entry that has no attributes?

0x0000002b:   DW_TAG_subprogram [3] *

0x0000002c:     DW_TAG_typedef [4]
                               DW_AT_type [DW_FORM_ref4]     (cu + 0x0040 =>
{0x00000040})
                               DW_AT_name [DW_FORM_strp]     (
.debug_str[0x00000060] = "T")
                               DW_AT_decl_file [DW_FORM_data1]      
("c:\temp\ICL\LB\retain.cpp")
                               DW_AT_decl_line [DW_FORM_data1]       (16)


Regards,
Amjad
From: David Blaikie [mailto:dblaikie at gmail.com]
Sent: Saturday, April 30, 2016 17:59
To: Aboud, Amjad <amjad.aboud at intel.com>
Cc: Adrian Prantl <aprantl at apple.com>; llvm-dev <llvm-dev at
lists.llvm.org>; Clang Dev <cfe-dev at lists.llvm.org>
Subject: Re: Debug info scope of explicit casting type does not seem correct

Yep, seems fine/reasonable to me. The pointer type has no logical scope so it
doesn't really matter where its DIE goes.

GCC does put the pointer type in the function scope in basic cases, but it can
also end up in other places. For example:

blaikie at blaikie-linux:~/dev$ cat func.cpp

void sink(void*);

template<typename T>

void f1() {

  T *t;

  sink(&t);

}

void f2() {

  struct foo { };

  f1<foo>();

}

blaikie at blaikie-linux:~/dev$ g++-4.7 -std=c++11 func.cpp -g -c &&
llvm-dwarfdump-tot -debug-dump=info func.o | grep DW_TAG

0x0000000b: DW_TAG_compile_unit [1] *

0x0000002d:   DW_TAG_subprogram [2] * // f2

0x00000051:     DW_TAG_lexical_block [3]

0x00000062:     DW_TAG_structure_type [4]

0x0000006b:   DW_TAG_subprogram [5] * // f1

0x00000087:     DW_TAG_template_type_parameter [6]

0x0000008e:     DW_TAG_lexical_block [7] *

0x0000009f:       DW_TAG_variable [8]

0x000000ab:       DW_TAG_pointer_type [9]  // foo*



& in fact, if you introduce another template that's similar to f1, its
variable's type is 0x00ab - so it points into f1's children. Seems GCC
puts it in whatever scope first references the pointer type.



I think it's probably as sensible, and a bit simpler, to put any such basic
types in the CU scope.



(granted, if GCC and Clang were really smart, the pointer type in f1 could be
pointer to 0x0087 - but that would really bloat the debug info (now every
different way of writing foo* in every different template would be a separate
type description... - that would probably be not good))

On Sat, Apr 30, 2016 at 3:32 AM, Aboud, Amjad <amjad.aboud at
intel.com<mailto:amjad.aboud at intel.com>> wrote:
Hi,
I am wondering if this behavior of creating debug info is correct.
A type in compile unit entry is pointing to a type under subprogram entry?!

This is the root cause of https://llvm.org/bugs/show_bug.cgi?id=27579

0x0000000b: DW_TAG_compile_unit [1] *

0x00000026:   DW_TAG_pointer_type [2]
                            DW_AT_type [DW_FORM_ref4]       (cu + 0x002c =>
{0x0000002c})

0x0000002b:   DW_TAG_subprogram [3] *

0x0000002c:     DW_TAG_typedef [4]
                               DW_AT_type [DW_FORM_ref4]     (cu + 0x0040 =>
{0x00000040})
                               DW_AT_name [DW_FORM_strp]     (
.debug_str[0x00000060] = "T")
                               DW_AT_decl_file [DW_FORM_data1]      
("c:\temp\ICL\LB\retain.cpp")
                               DW_AT_decl_line [DW_FORM_data1]       (16)

0x00000037:     NULL


command line:
clang -cc1 -triple i386-apple-ios9.0.0 -emit-obj -debug-info-kind=limited -O2
test.cpp –o - | llvm-dwarfdump -debug-dump=info -
> cat test.cppclass A {
public:
  int x;
};


class B {
public:
  typedef A type;
};

template<typename X>
int foo(void* in) {
  typedef typename X::type T;
  const T* p = (T*) in;
  return p->x;
}

int bar() {
A a;
  return foo<B>(&a);
}

Reason for this behavior is the explicit cast “(T*)“, which leads into the
following IR:

!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer:
"clang version 3.9.0 (trunk 267335)", isOptimized: true,
runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3)
!3 = !{!4}
!4 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !5, size: 32, align: 32)
<----------------- No Scope, leads to compile unit scope!!
!5 = !DIDerivedType(tag: DW_TAG_typedef, name: "T", scope: !7, file:
!6, line: 16, baseType: !20)
!7 = distinct !DISubprogram(name: "foo<B>", linkageName:
"_Z3fooI1BEiPv", scope: !6, file: !6, line: 15, type: !8, isLocal:
false, isDefinition: true, scopeLine: 15, flags: DIFlagPrototyped, isOptimized:
true, unit: !0, templateParams: !12, variables: !15)


Thanks,
Amjad


---------------------------------------------------------------------
Intel Israel (74) Limited

This e-mail and any attachments may contain confidential material for
the sole use of the intended recipient(s). Any review or distribution
by others is strictly prohibited. If you are not the intended
recipient, please contact the sender and delete all copies.

---------------------------------------------------------------------
Intel Israel (74) Limited

This e-mail and any attachments may contain confidential material for
the sole use of the intended recipient(s). Any review or distribution
by others is strictly prohibited. If you are not the intended
recipient, please contact the sender and delete all copies.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20160507/15cd783d/attachment-0001.html>

Possibly Parallel Threads

Search for more apparently analagous threads

llvm dev - May 2016 - Debug info scope of explicit casting type does not seem correct

[llvm-dev] Debug info scope of explicit casting type does not seem correct

[llvm-dev] Debug info scope of explicit casting type does not seem correct

[llvm-dev] Debug info scope of explicit casting type does not seem correct

Possibly Parallel Threads