Paragma Pack() in vxWorks
Krishna Kishore Reddy Sureddy
What is sigificance of argument passed to #pragma pack() in "C" and
"vxWorks".
Thanks and Regards,
S.K.K.Reddy.
Dave Korn
<9gugoh$9f7$1...@overload.lbl.gov>...
>Hi vxWorks Gurus,
>What is sigificance of argument passed to #pragma pack() in "C" and
>"vxWorks".
Alas, the only documentation on these is buried deep in the instructions
for how to modify and retarget the compiler to a new cpu. Here they are: I
don't know whether or not the #pragma pack (pull/push) variants are
implemented or not.
----snip---
`HANDLE_SYSV_PRAGMA'
Define this macro (to a value of 1) if you want the System V style
pragmas `#pragma pack(<n>)' and `#pragma weak <name> [=<value>]'
to be supported by gcc.
The pack pragma specifies the maximum alignment (in bytes) of
fields within a structure, in much the same way as the
`__aligned__' and `__packed__' `__attribute__'s do. A pack value
of zero resets the behaviour to the default.
The weak pragma only works if `SUPPORTS_WEAK' and
`ASM_WEAKEN_LABEL' are defined. If enabled it allows the creation
of specifically named weak labels, optionally with a value.
`HANDLE_PRAGMA_PACK_PUSH_POP'
Define this macro (to a value of 1) if you want to support the
Win32 style pragmas `#pragma pack(push,<n>)' and `#pragma
pack(pop)'. The pack(push,<n>) pragma specifies the maximum
alignment (in bytes) of fields within a structure, in much the
same way as the `__aligned__' and `__packed__' `__attribute__'s
do. A pack value of zero resets the behaviour to the default.
Successive invocations of this pragma cause the previous values to
be stacked, so that invocations of `#pragma pack(pop)' will return
to the previous value.
----snip---
DaveK
--
They laughed at Galileo. They laughed at Copernicus. They laughed at
Columbus. But remember, they also laughed at Bozo the Clown.
Melvin Gardipee >
The GNU ToolKit Users Guide only reference to #pragma gives
reasons for not using them ending with the quote "It is basically a
mistake to use #pragma for anything". Use of #pragma in the 1.34
version of GNU C compiler would cause the cause the compiler to stop
and launch a computer game. It was their idea of implementing the
ANSI standard 'arbitrary implementation-defined effect'.
I would avoid using #pragma with GNU compilers. If you are
communicating with a VxWorks based system from a different OS,
#pragma pack your structures to match the VxWorks layout. For Win32
to VxWorks communication, you can #pragma pack on the Win32 side
in a common header file using something like this:
#ifdef WIN32
#pragma pack( push, some_unique_name )
#pragma pack(8)
#endif
<COMMON TYPEDEF'S HERE>
#ifdef WIN32
#pragma pack( pop, some_unique_name )
#endif
The above example works for PPC architectures.
Regards,
Melvin Gardipee