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Started by Charles Blair
Thu, 25 Sep 1986 02:06
A peculiar MASM problem
Author: Charles Blair
Date: Thu, 25 Sep 1986 02:06
Date: Thu, 25 Sep 1986 02:06
37 lines
2402 bytes
2402 bytes
I can't think of a better place to request help on the following problem, so here goes. I have been working on an 8086 assembler problem that has seven source files. I installed push/pop in it and have been using it for a while without problems. For greater ease of maintenance, I broke one module into two. Since then, push only works the first time it is invoked, not the second and subsequent times; I've determined that the push proc is being called, but it seems to return to the caller without executing any of the code. From then on the program seems to work fine: it doesn't hang. However, if executing the program from SYMDEB, I have no problems pushing to the exec as many times as I want (so the debugger per se is useless in helping me to localize the problem). Also, if I run the program as a child of itself (i.e., push out of it the first time, then reload it), I also have no problems pushing out at will. But when I exit to DOS and then exit back to the parent, again I can't push, since I've already pushed once. One final observation: if I eliminate one of the source files in the link step (and I've tried it with three files in turn, with the same result), push/pop again works fine, every time. I've looked at the obvious, like not terminating data segments properly, not deallocating too much memory before pushing, and so on. Clearly, I can't expect any reader of this to help me on the basis of the short description of the problem I have given, unless such a reader has encountered a similar problem. I'd be interested in hearing from any such reader, since I can't formulate a proper hypothesis as to the cause of the problem given the program behavior clues as indicated above. Thanks in advance. -- Charles Blair ..!ihnp4!gargoyle!sphinx!cjdb The University of Chicago lib.cb%chip@UChicago.Bitnet
Re: A peculiar MASM problem
Author: Charles Blair
Date: Fri, 26 Sep 1986 01:40
Date: Fri, 26 Sep 1986 01:40
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2230 bytes
Well, I've solved my own problem, and I post the solution in case anyone else runs into the problem described in the original posting, and in case some knowledgeable person can offer some further clarificatory words. Both Norton (Programmer's Guide) and Ray Duncan in the new *Advanced MSDOS* (Microsoft Press, 1986) point out that the SS and SP registers need to be saved into variables within the code segment before executing the EXEC function call, and need to be restored from those variables right after control is returned to the program. I had been doing this right before pushing all the other registers onto the stack in preparation for making the call itself. This worked, except under the conditions described in the previous posting. I have since moved the definition of these variables to right after the beginning of the code segment in the same module, i.e., out of the proc that made the EXEC call. This seems to work fine. I decided that this might be the problem after determining that when push failed, it failed right after stepping through the two defines, one for SP and one for SS. Right after those two lines were "executed," the code seemed to return to the caller: the rest of the proc never got executed. I'd appreciate hearing form anyone with a firmer grasp of what really went wrong here, i.e., what the real pitfalls are in making this call, and I apologize to the non-MASMers who might be reading this. Thanks in advance. -- Charles Blair ..!ihnp4!gargoyle!sphinx!cjdb The University of Chicago lib.cb%chip@UChicago.Bitnet
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