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GCC 4.7.0 breaks __attribute__((packed)) behavior on... (Developers)

posted by RayeR , CZ, 04.09.2012, 18:53

Hi,
maybe some of you are using mingw32 and/or writing portable code for 32/64bit systems so it may save your time on hunting bugs. I just recompiled my KMD under new mingw32 4.7.0 and got a crash. After night tracking I found that the problem is in size of structure:


typedef struct {                       // 48-bit adresa GDT/IDT
  Word limit;                          // size limit of GDT [Bytes-1]
  DWord base;                          // linear base address of the GDT in physical memory
} __attribute__((packed)) GDTR;


You may think that __attribute__((packed)) save your ass and will be always 6 Bytes. Forget, not now, world is going mad and packing behaves differently.
To fix it, it's needed to add -mno-ms-bitfields gcc option since version 4.7.0.
But not at all systems. DJGPP 4.7.1 doesn't need it. But mingw32 and 64-bit linux gcc yes. More at https://lists.gnu.org/archive/html/qemu-devel/2012-07/msg02240.html

---
DOS gives me freedom to unlimited HW access.

Complete thread:

• GCC 4.7.0 breaks __attribute__((packed)) behavior on... - RayeR, 04.09.2012, 18:53 (Developers)
  • GCC 4.7.0 breaks __attribute__((packed)) behavior on... - Rugxulo, 04.09.2012, 23:16
    • GCC 4.7.0 breaks __attribute__((packed)) behavior on... - RayeR, 05.09.2012, 03:46
      • GCC 4.7.0 breaks __attribute__((packed)) behavior on... - Rugxulo, 05.09.2012, 11:26
        • GCC 4.7.0 breaks __attribute__((packed)) behavior on... - RayeR, 05.09.2012, 19:09