AIX To Linux Migration

**Testing** · 11-08-2011

Hi All,

We are currently migrating C++ code from AIX to Linux.
Visual Age C++ was the compiler used in AIX whereas g++ is used in Linux.
There are many pragmas used in the current code in AIX. We are looking for their equivalent in g++. If anyone has any idea regarding this, kindly update..

Some of the pragmas used in the code are given below,
#pragma object_model (compat)

#pragma info(none)
#pragma report(level, E)
#pragma info(restore)

#if __IBMCPP__ >= 400
#pragma namemangling(compat)
#endif

#pragma enum(int)
#pragma options align = power
....
#pragma options align = reset

#pragma enum(pop)
#pragma report(pop)
#pragma info(restore)

#if __IBMCPP__ >= 500
#pragma namemangling(pop)
#endif

Thanks & Regards,

**jimblumberg** · 11-08-2011

I would start with comparing these two links: IBM pragma descriptions and GCC Option Summary.

Jim

**Testing** · 11-08-2011

Hi Jim

I had also compared the options provided by both the compilers but couldn't find the exact options to be used in g++ for the pragmas that I have given in my earlier post.

It will be very helpful if you can provide any information related to this.

Thanks

**jimblumberg** · 11-08-2011

I doubt very much that you will find "exact" matches. You need to find the closest match.

It will be very helpful if you can provide any information related to this.

I suggest you carefully read the descriptions of the IBM pragmas and then find the gcc equivalent settings.
For example for #pragma report(level, E) the relevant section of gcc is: Options to Request or Suppress Warnings. And I would recommend that you start by using higher warning levels than the original program.

Jim

**Codeplug** · 11-08-2011

I'd say you can skip all of those for the g++ build.

gg

**Salem** · 11-08-2011

I'd second codeplug's answer.
Just delete the whole mess of #pragma's (most seem like ugly hacks anyway) and see what a nice clean compile does for you.

Post your results.

**Testing** · 11-09-2011

We cannot actually skip all the pragmas.

For eg: In the code we have,

Code:

#pragma options align=packed

struct s1{
  long l;
  short s;
  char c[9];
};

struct s2{
...
...
};

....

#pragma options align=reset

In this case if we skip these pragmas and compile using g++, there won't be any compilation error but the data that we get while executing the program will be incorrect since packing is not done.

**KCfromNC** · 11-09-2011

Structure-Packing Pragmas - Using the GNU Compiler Collection (GCC)

**Salem** · 11-09-2011

An opportunity then to improve the code so that it no longer depends on arbitrary "pack" features of a compiler.

For one thing, if you move to another architecture with a different endian, then you're screwed anyway, as there is no pragma to sort that mess out.

**KCfromNC** · 11-10-2011

Good point. If you're using struct packing to make sure I/O is efficient, it's better to do it using some smarts in the serialization instead of forcing the IO format to match the in-memory version. If you're doing it to optimize memory usage, it's probably premature to do so when jumping to a new compiler. If you're trying to do something else, ask and we may have ideas.

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