Opened 3 years ago

Closed 3 years ago

Last modified 18 months ago

#63490 closed defect (fixed)

libdazzle @3.38.0_0: Static assert failure on PowerPC due to struct packing issue with different version of gcc

Reported by: evanmiller (Evan Miller) Owned by: evanmiller (Evan Miller)
Priority: Normal Milestone:
Component: ports Version: 2.7.1
Keywords: Cc: kencu (Ken)
Port: libdazzle

Description

:info:build In file included from /opt/local/lib/glib-2.0/include/glibconfig.h:9:0,
:info:build                  from /opt/local/include/glib-2.0/glib/gtypes.h:32,
:info:build                  from /opt/local/include/glib-2.0/glib/galloca.h:32,
:info:build                  from /opt/local/include/glib-2.0/glib.h:30,
:info:build                  from /opt/local/include/glib-2.0/gobject/gbinding.h:28,
:info:build                  from /opt/local/include/glib-2.0/glib-object.h:23,
:info:build                  from ../libdazzle-3.38.0/src/search/dzl-fuzzy-mutable-index.h:22,
:info:build                  from ../libdazzle-3.38.0/src/search/dzl-fuzzy-mutable-index.c:24:
:info:build /opt/local/include/glib-2.0/glib/gmacros.h:738:31: error: static assertion failed: "Expression evaluates to false"
:info:build  #define G_STATIC_ASSERT(expr) _Static_assert (expr, "Expression evaluates to false")
:info:build                                ^
:info:build ../libdazzle-3.38.0/src/search/dzl-fuzzy-mutable-index.c:70:1: note: in expansion of macro 'G_STATIC_ASSERT'
:info:build  G_STATIC_ASSERT (sizeof(DzlFuzzyMutableIndexItem) == 6);
:info:build  ^~~~~~~~~~~~~~~
:info:build ninja: build stopped: subcommand failed.

Context:

#pragma pack(push, 1)
typedef struct
{
  guint64 id : 32;
  guint64 pos : 16;
} DzlFuzzyMutableIndexItem;
#pragma pack(pop)

In a test program, the above structure is 8 bytes but libdazzle is expecting it to be 6 bytes.

sysinfo

:debug:sysinfo Mac OS X 10.4.11 (darwin/8.11.0) arch powerpc
:debug:sysinfo MacPorts 2.7.1
:debug:sysinfo Xcode 2.5
:debug:sysinfo SDK 10.4
:debug:sysinfo MACOSX_DEPLOYMENT_TARGET: 10.4

Full log to follow.

Attachments (1)

libdazzle-main.log (220.4 KB) - added by evanmiller (Evan Miller) 3 years ago.

Download all attachments as: .zip

Change History (15)

Changed 3 years ago by evanmiller (Evan Miller)

Attachment: libdazzle-main.log added

comment:2 Changed 3 years ago by evanmiller (Evan Miller)

Thanks for the link. I'm still confused why there are 2 bytes of end padding with pack(push, 1) in place. Perhaps this is controlled by a separate pragma or flag.

comment:3 Changed 3 years ago by kencu (Ken)

how does this work, exactly?

  guint64 pos : 16;

If a guint64 needs 4 bytes, how does adding the " : 16" somehow make it a two-byter?

I haven't seen this construct much before, or at least haven't noticed it...

comment:5 Changed 3 years ago by evanmiller (Evan Miller)

Well, it looks like libdazzle has updated this code for Win32:

https://gitlab.gnome.org/GNOME/libdazzle/-/blob/master/src/search/dzl-fuzzy-mutable-index.c#L62-75

Likely we'll need to include PPC in that ifdef or patch similarly

comment:6 Changed 3 years ago by evanmiller (Evan Miller)

Actually, the Win32 code doesn't solve the problem on PPC, so further research is needed.

comment:7 Changed 3 years ago by kencu (Ken)

interesting (Tiger PPC):

$ cat packcheck.c
#include <stdio.h>
#include <stdint.h>

int main(void) {

    #pragma option align=mac68k
    typedef struct
    {
    uint32_t id : 32;
    uint32_t  pos : 16;
    } KenStruct;
    
    KenStruct mystruct;
    
    printf("%i\n\n", sizeof(KenStruct));
    return 0;
}
$ gcc-mp-7 packcheck.c
$ ./a.out
8
$ gcc-apple-4.2 packcheck.c
$ ./a.out
8
$ gcc-apple-4.2 -malign-mac68k packcheck.c
$ ./a.out
6
$ gcc-mp-7 -malign-mac68k packcheck.c
gcc-mp-7: error: unrecognized argument in option '-malign-mac68k'
gcc-mp-7: note: valid arguments to '-malign-' are: natural power
Last edited 3 years ago by kencu (Ken) (previous) (diff)

comment:8 Changed 3 years ago by evanmiller (Evan Miller)

Interestingly, just the regular pack directives work as expected with gcc-apple-4.2:

#include <stdint.h>

#pragma pack(push, 1)
typedef struct
{
  uint32_t id;
  uint16_t pos;
} DzlFuzzyMutableIndexItem;
#pragma pack(pop)

int main() {
    return sizeof(DzlFuzzyMutableIndexItem);
}
$ gcc-mp-7 test-pack.c && ./a.out
$ echo $?
8

$ gcc-apple-4.2 test-pack.c && ./a.out
$ echo $?
6

So the struct-padding algorithm changed at some point.

comment:9 Changed 3 years ago by kencu (Ken)

This works properly:

$ cat packcheck.c
#include <stdio.h>
#include <stdint.h>

int main(void) {

    typedef struct __attribute__((packed))
    {
    uint32_t id : 32;
    uint16_t  pos : 16;
    } KenStruct;
    
    KenStruct mystruct;
    
    printf("%i\n\n", sizeof(KenStruct));
    return 0;
}
$ gcc-mp-7 packcheck.c
$ ./a.out
6
Last edited 3 years ago by kencu (Ken) (previous) (diff)

comment:10 Changed 3 years ago by kencu (Ken)

and back to the original, looks pretty good:

$ cat packcheck.c
#include <stdio.h>
#include <glib.h>

int main(void) {

    typedef struct __attribute__((packed))
    {
    guint64 id : 32;
    guint64 pos : 16;
    } KenStruct;
    
    KenStruct mystruct;
    
    printf("%i\n\n", sizeof(KenStruct));
    return 0;

}
$ gcc-mp-7 `pkg-config --cflags glib-2.0` packcheck.c

$ ./a.out
6

so that looks like our solution.

Last edited 3 years ago by kencu (Ken) (previous) (diff)

comment:11 Changed 3 years ago by evanmiller (Evan Miller)

Nice find! Wonder whether that's a GCC bug and whether GCC11 has the same behavior.

Anyway, we have a workaround now. I'll get a patch going, assuming everything else compiles OK.

comment:12 Changed 3 years ago by evanmiller (Evan Miller)

Owner: set to evanmiller
Resolution: fixed
Status: newclosed

comment:13 Changed 18 months ago by kencu (Ken)

Summary: libdazzle @3.38.0_0: Static assert failure on PowerPClibdazzle @3.38.0_0: Static assert failure on PowerPC due to struct packing issue with different version of gcc

comment:14 in reply to:  11 Changed 18 months ago by barracuda156

Replying to evanmiller:

Nice find! Wonder whether that's a GCC bug and whether GCC11 has the same behavior.

Anyway, we have a workaround now. I'll get a patch going, assuming everything else compiles OK.

Yes, as well as GCC12: https://github.com/macports/macports-ports/pull/18872#issuecomment-1568714259

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