The following code will result in a bus error on Mac OS X 10.8.2 using DMD 2.062 compiled for 32bit (segfault on 64bit). A couple of notes:

* This code runs fine on Mac OS X 10.6.3
* It seems the struct has to be over 64 bits in size
* "foo" need to take an argument

Dissassembly at the bottom.

I think this is the same problem I had with interfacing with the objc_msgSend_stret function, see other post:

http://forum.dlang.org/thread/kkefk8$2663$1@digitalmars.com

C code:

struct Foo
{
    int a;
    int b;
    int c;
};

typedef struct Foo Foo;

Foo foo (int a)
{
    Foo f;
    f.a = 1;
    f.b = 2;
    f.c = 3;
    return f;
}

D code:

struct Foo
{
    int a;
    int b;
    int c;
}

extern (C) Foo foo (int a);

Foo bar ()
{
    return foo(0);
}

extern (C) int printf(in char*, ...);

void main ()
{
    auto frame = bar();
    printf("a=%d b=%d c=%d\n".ptr, frame.a, frame.b, frame.c);
}

GDB session with dissassembly:

http://pastebin.com/rguwXucR

Dissassembly of the corresponding C program compiled with Clang:

http://pastebin.com/MG8Tnkzp

Dissassembly of "foo" on Mac OS X 10.8.2 using Clang 4.1:

http://pastebin.com/0jKqksxx

Dissassembly of "foo" on Mac OS X 10.6.3 using Clang 1.5:

http://pastebin.com/kbdfuVcB

-- 
/Jacob Carlborg

On 2013-04-16 21:26, Jacob Carlborg wrote:
> The following code will result in a bus error on Mac OS X 10.8.2 using
> DMD 2.062 compiled for 32bit (segfault on 64bit). A couple of notes:
>
> * This code runs fine on Mac OS X 10.6.3
> * It seems the struct has to be over 64 bits in size
> * "foo" need to take an argument

If I a store the return value of "foo" in a temporary variable in "bar" the bus error goes away.

-- 
/Jacob Carlborg

On Tuesday, 16 April 2013 at 19:26:09 UTC, Jacob Carlborg wrote:
> The following code will result in a bus error on Mac OS X 10.8.2 using DMD 2.062 compiled for 32bit (segfault on 64bit). A couple of notes:
>
> * This code runs fine on Mac OS X 10.6.3
> * It seems the struct has to be over 64 bits in size
> * "foo" need to take an argument
>
> Dissassembly at the bottom.
>
> I think this is the same problem I had with interfacing with the objc_msgSend_stret function, see other post:
>
> http://forum.dlang.org/thread/kkefk8$2663$1@digitalmars.com
>
> C code:
>
> struct Foo
> {
>     int a;
>     int b;
>     int c;
> };
>
> typedef struct Foo Foo;
>
> Foo foo (int a)
> {
>     Foo f;
>     f.a = 1;
>     f.b = 2;
>     f.c = 3;
>     return f;
> }
>
> D code:
>
> struct Foo
> {
>     int a;
>     int b;
>     int c;
> }
>
> extern (C) Foo foo (int a);
>
> Foo bar ()
> {
>     return foo(0);
> }
>
> extern (C) int printf(in char*, ...);
>
> void main ()
> {
>     auto frame = bar();
>     printf("a=%d b=%d c=%d\n".ptr, frame.a, frame.b, frame.c);
> }
>
> GDB session with dissassembly:
>
> http://pastebin.com/rguwXucR
>
> Dissassembly of the corresponding C program compiled with Clang:
>
> http://pastebin.com/MG8Tnkzp
>
> Dissassembly of "foo" on Mac OS X 10.8.2 using Clang 4.1:
>
> http://pastebin.com/0jKqksxx
>
> Dissassembly of "foo" on Mac OS X 10.6.3 using Clang 1.5:
>
> http://pastebin.com/kbdfuVcB

Some observations:

Assuming main is doing everything properly, it's passing a pointer to 12 bytes of stack space to bar in eax (as per the D ABI). bar then puts that pointer on the stack for foo (as per the IA32 OS X ABI). However, it looks to me like it's in the wrong place, because of this line:
0x00002673 <D4test3barFZS4test3Foo+11>: sub    $0x8,%esp

This is just from a quick glance, I may have added my hexes wrongly.

On 2013-04-17 01:03, John Colvin wrote:

> Some observations:
>
> Assuming main is doing everything properly, it's passing a pointer to 12
> bytes of stack space to bar in eax (as per the D ABI). bar then puts
> that pointer on the stack for foo (as per the IA32 OS X ABI). However,
> it looks to me like it's in the wrong place, because of this line:
> 0x00002673 <D4test3barFZS4test3Foo+11>: sub    $0x8,%esp
>
> This is just from a quick glance, I may have added my hexes wrongly.

I don't know, that's why I'm asking here :) This is what Martin Nowak said in the bug report:

"Seems like OSX deviates from the SysV IA-32 ABI for memory struct returns. The callee does NOT return the hidden pointer in EAX.
Instead the caller has to use the value passed as argument."

http://d.puremagic.com/issues/show_bug.cgi?id=9931#c7

The ABI documentation says:

"When a function returns a structure or union larger than 8 bytes, the caller passes a pointer to appropriate storage as the first argument to the function."

And:

"The called function returns structures according to their aligned size.

* Structures 1 or 2 bytes in size are placed in EAX.
* Structures 4 or 8 bytes in size are placed in: EAX and EDX.
* Structures of other sizes are placed at the address supplied by the caller. For example, the C++ language occasionally forces the compiler to return a value in memory when it would normally be returned in registers. See “Passing Arguments” for more information."

http://developer.apple.com/library/mac/#documentation/DeveloperTools/Conceptual/LowLevelABI/130-IA-32_Function_Calling_Conventions/IA32.html#//apple_ref/doc/uid/TP40002492-SW4

-- 
/Jacob Carlborg

On Tuesday, 16 April 2013 at 23:03:44 UTC, John Colvin wrote:
> On Tuesday, 16 April 2013 at 19:26:09 UTC, Jacob Carlborg wrote:
>> The following code will result in a bus error on Mac OS X 10.8.2 using DMD 2.062 compiled for 32bit (segfault on 64bit). A couple of notes:
>>
>> * This code runs fine on Mac OS X 10.6.3
>> * It seems the struct has to be over 64 bits in size
>> * "foo" need to take an argument
>>
>> Dissassembly at the bottom.
>>
>> I think this is the same problem I had with interfacing with the objc_msgSend_stret function, see other post:
>>
>> http://forum.dlang.org/thread/kkefk8$2663$1@digitalmars.com
>>
>> C code:
>>
>> struct Foo
>> {
>>    int a;
>>    int b;
>>    int c;
>> };
>>
>> typedef struct Foo Foo;
>>
>> Foo foo (int a)
>> {
>>    Foo f;
>>    f.a = 1;
>>    f.b = 2;
>>    f.c = 3;
>>    return f;
>> }
>>
>> D code:
>>
>> struct Foo
>> {
>>    int a;
>>    int b;
>>    int c;
>> }
>>
>> extern (C) Foo foo (int a);
>>
>> Foo bar ()
>> {
>>    return foo(0);
>> }
>>
>> extern (C) int printf(in char*, ...);
>>
>> void main ()
>> {
>>    auto frame = bar();
>>    printf("a=%d b=%d c=%d\n".ptr, frame.a, frame.b, frame.c);
>> }
>>
>> GDB session with dissassembly:
>>
>> http://pastebin.com/rguwXucR
>>
>> Dissassembly of the corresponding C program compiled with Clang:
>>
>> http://pastebin.com/MG8Tnkzp
>>
>> Dissassembly of "foo" on Mac OS X 10.8.2 using Clang 4.1:
>>
>> http://pastebin.com/0jKqksxx
>>
>> Dissassembly of "foo" on Mac OS X 10.6.3 using Clang 1.5:
>>
>> http://pastebin.com/kbdfuVcB
>
> Some observations:
>
> Assuming main is doing everything properly, it's passing a pointer to 12 bytes of stack space to bar in eax (as per the D ABI). bar then puts that pointer on the stack for foo (as per the IA32 OS X ABI). However, it looks to me like it's in the wrong place, because of this line:
> 0x00002673 <D4test3barFZS4test3Foo+11>: sub    $0x8,%esp
>
> This is just from a quick glance, I may have added my hexes wrongly.

I was wrong. Ignore the previous post.

On Tuesday, 16 April 2013 at 19:26:09 UTC, Jacob Carlborg wrote:
> The following code will result in a bus error on Mac OS X 10.8.2 using DMD 2.062 compiled for 32bit (segfault on 64bit). A couple of notes:
>
> * This code runs fine on Mac OS X 10.6.3
> * It seems the struct has to be over 64 bits in size
> * "foo" need to take an argument
>
> Dissassembly at the bottom.
>
> I think this is the same problem I had with interfacing with the objc_msgSend_stret function, see other post:
>
> http://forum.dlang.org/thread/kkefk8$2663$1@digitalmars.com
>
> C code:
>
> struct Foo
> {
>     int a;
>     int b;
>     int c;
> };
>
> typedef struct Foo Foo;
>
> Foo foo (int a)
> {
>     Foo f;
>     f.a = 1;
>     f.b = 2;
>     f.c = 3;
>     return f;
> }
>
> D code:
>
> struct Foo
> {
>     int a;
>     int b;
>     int c;
> }
>
> extern (C) Foo foo (int a);
>
> Foo bar ()
> {
>     return foo(0);
> }
>
> extern (C) int printf(in char*, ...);
>
> void main ()
> {
>     auto frame = bar();
>     printf("a=%d b=%d c=%d\n".ptr, frame.a, frame.b, frame.c);
> }
>
> GDB session with dissassembly:
>
> http://pastebin.com/rguwXucR
>
> Dissassembly of the corresponding C program compiled with Clang:
>
> http://pastebin.com/MG8Tnkzp
>
> Dissassembly of "foo" on Mac OS X 10.8.2 using Clang 4.1:
>
> http://pastebin.com/0jKqksxx
>
> Dissassembly of "foo" on Mac OS X 10.6.3 using Clang 1.5:
>
> http://pastebin.com/kbdfuVcB

Martins reply in the bug report correctly identifies the problem, it's a bug in dmds implementation of the OS X IA32 ABI.

This is quite a severe bug, it's only by luck that eax was set to 0 causing an immediate error.

I suggest it should be marked critical.

On 2013-04-17 12:05, John Colvin wrote:

> Martins reply in the bug report correctly identifies the problem, it's a
> bug in dmds implementation of the OS X IA32 ABI.

I see. I'm still wondering why it works on Mac OS X 10.6.3, just luck?

> This is quite a severe bug, it's only by luck that eax was set to 0
> causing an immediate error.
>
> I suggest it should be marked critical.

Ok, perhaps we can come up with a better description for the issue as well.

-- 
/Jacob Carlborg

On Wednesday, 17 April 2013 at 11:14:52 UTC, Jacob Carlborg wrote:
> On 2013-04-17 12:05, John Colvin wrote:
>
>> Martins reply in the bug report correctly identifies the problem, it's a
>> bug in dmds implementation of the OS X IA32 ABI.
>
> I see. I'm still wondering why it works on Mac OS X 10.6.3, just luck?

clang just happened to put the arguments to foo in to registers different on 10.6.3
Instead of loading the 0 argument in to eax it loaded the pointer to the struct like it would in system V ABI (linux)

I have no idea whether this is a complete coincidence, or whether clang has changed it's approach to the OS X abi, or whether the ABI itself has changed.

On 2013-04-17 13:43, John Colvin wrote:

> clang just happened to put the arguments to foo in to registers
> different on 10.6.3
> Instead of loading the 0 argument in to eax it loaded the pointer to the
> struct like it would in system V ABI (linux)
>
> I have no idea whether this is a complete coincidence, or whether clang
> has changed it's approach to the OS X abi, or whether the ABI itself has
> changed.

Ok, I see. The docs for the ABI says:

The called function returns structures according to their aligned size.

* Structures 1 or 2 bytes in size are placed in EAX.
* Structures 4 or 8 bytes in size are placed in: EAX and EDX.
* Structures of other sizes are placed at the address supplied by the caller. For example, the C++ language occasionally forces the compiler to return a value in memory when it would normally be returned in registers. See “Passing Arguments” for more information.



-- 
/Jacob Carlborg