Q67357: Void _saveregs Function Does Not Preserve AX Register

Article: Q67357
Product(s): See article
Version(s): 
Operating System(s): 6.00 6.00a | 6.00 6.00a
Keyword(s): MS-DOS | OS/2 | mspl13_c
Last Modified: 15-FEB-1991

ENDUSER | s_quickc buglist6.00 buglist6.00a

Functions with a void return type that are declared with the _saveregs
attribute do not preserve the AX register. An arbitrary return value
is stored in AX unnecessarily.

The C online help states the following:

   The _saveregs keyword causes the compiler to generate code that
   saves and restores all CPU registers when entering and exiting the
   specified function. Note that _saveregs does not restore registers
   used for a return value (the AX register, or AX and DX).

The second sentence states that AX will not be preserved whenever
there is a return value, but a void function has no return value.
Thus, there is no reason the AX register should not be preserved.

Microsoft has confirmed this to be a problem in C versions 6.00 and
6.00a and QuickC version 2.50 (buglist2.50). We are researching this
problem and will post new information here as it becomes available.

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