This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

problem

i use keil arm rvct
and have small problem
RVCT have no #pragma pack(1)
but when i got program from my friend i didnt see this program and RVCT didnt say warning about this command - and i have problem
because this command destroy execute program
for example

#pragma pack(1)

typedef struct
{ unsigned char command; unsigned long packets; unsigned char reserved[3];

} COMMAND2;

int main()
{ COMMAND2 cmd2; unsigned long Size;

cmd2.command = 0x01; cmd2.packets = 1000; Size = cmd2.packets; Size = cmd2.command;
}

when run this program Size <> 1 at the end !!!

undetermine command #pragma pack(1) create error and compiler dont say warning about this command
if correct program for RVTC

typedef __packed struct
{ unsigned char command; unsigned long packets; unsigned char reserved[3];

} COMMAND2;

int main()
{ COMMAND2 cmd2; unsigned long Size;

cmd2.command = 0x01; cmd2.packets = 1000; Size = cmd2.packets; Size = cmd2.command;
}

we will get ok result

Parents
  • if you have no LICENSE - example for evalution version

    IDE-Version:
    µVision3 V3.50
    Copyright (c) Keil Elektronik GmbH / Keil Software, Inc. 1995 - 2007

    Tool Version Numbers:
    Toolchain Path: BIN30\
    C Compiler: ARM/Thumb C/C++ Compiler, RVCT3.0 [Build 951] for uVision [Evaluation]
    Assembler: ARM/Thumb Macro Assembler, RVCT3.0 [Build 951] for uVision [Evaluation]
    Linker/Locator: ARM Linker, RVCT3.0 [Build 951] for uVision [Evaluation]
    Librarian: ARM Archiver, RVCT3.0 [Build 951] for uVision
    Hex Converter: ARM FromELF, RVCT3.0 [Build 951] for uVision [Evaluation]
    CPU DLL: SARM.DLL V3.04
    Dialog DLL: DARMP.DLL V1.13
    Target DLL: BIN\UL2ARM.DLL V1.26
    Dialog DLL: TARMP.DLL V1.11f

    #pragma pack(1)
        12: {
        13:         COMMAND2 cmd2;
        14:         volatile unsigned long Size;
        15:
    0x000001B0  E24DD008  SUB       R13,R13,#0x00000008
        16:         cmd2.command = 0x01;
    0x000001B4  E3A00001  MOV       R0,#0x00000001
    0x000001B8  E5CD0000  STRB      R0,[R13]
        17:         cmd2.packets = 1000;
    0x000001BC  E3A00FFA  MOV       R0,#0x000003E8
    0x000001C0  E28DC001  ADD       R12,R13,#0x00000001
    0x000001C4  E58C0000  STR       R0,[R12]
        18:         Size = cmd2.packets;
    0x000001C8  E28DC001  ADD       R12,R13,#0x00000001
    0x000001CC  E59C1000  LDR       R1,[R12]
        19:         Size = cmd2.command;
        20:
        21:
    0x000001D0  E5DD1000  LDRB      R1,[R13]
        22: }
    

Reply
  • if you have no LICENSE - example for evalution version

    IDE-Version:
    µVision3 V3.50
    Copyright (c) Keil Elektronik GmbH / Keil Software, Inc. 1995 - 2007

    Tool Version Numbers:
    Toolchain Path: BIN30\
    C Compiler: ARM/Thumb C/C++ Compiler, RVCT3.0 [Build 951] for uVision [Evaluation]
    Assembler: ARM/Thumb Macro Assembler, RVCT3.0 [Build 951] for uVision [Evaluation]
    Linker/Locator: ARM Linker, RVCT3.0 [Build 951] for uVision [Evaluation]
    Librarian: ARM Archiver, RVCT3.0 [Build 951] for uVision
    Hex Converter: ARM FromELF, RVCT3.0 [Build 951] for uVision [Evaluation]
    CPU DLL: SARM.DLL V3.04
    Dialog DLL: DARMP.DLL V1.13
    Target DLL: BIN\UL2ARM.DLL V1.26
    Dialog DLL: TARMP.DLL V1.11f

    #pragma pack(1)
        12: {
        13:         COMMAND2 cmd2;
        14:         volatile unsigned long Size;
        15:
    0x000001B0  E24DD008  SUB       R13,R13,#0x00000008
        16:         cmd2.command = 0x01;
    0x000001B4  E3A00001  MOV       R0,#0x00000001
    0x000001B8  E5CD0000  STRB      R0,[R13]
        17:         cmd2.packets = 1000;
    0x000001BC  E3A00FFA  MOV       R0,#0x000003E8
    0x000001C0  E28DC001  ADD       R12,R13,#0x00000001
    0x000001C4  E58C0000  STR       R0,[R12]
        18:         Size = cmd2.packets;
    0x000001C8  E28DC001  ADD       R12,R13,#0x00000001
    0x000001CC  E59C1000  LDR       R1,[R12]
        19:         Size = cmd2.command;
        20:
        21:
    0x000001D0  E5DD1000  LDRB      R1,[R13]
        22: }
    

Children
  • A summary for those who don't want to wade through 22 posts to figure out what the issue here is!!

    #pragma pack(1) is not supported by the RVCT compiler according to the compiler manual. The correct way to pack a structure is using the __packed attribute.

    As Dan states, the compiler is free to ignore with a warning any pragmas that it doesn't understand.

    However the issue here is – as I understand the description – is that the compiler is recognising #pragma pack(1) as a directive to pack the structure with one byte alignment.

    It is not however generating the code that will handle accessing the structure in an unaligned way like the code generated when the __packed attribute is used.

    If this is true, then Keil support should have a look at this and maybe update the compiler manual or remove this #pragma from the compiler.

  • "As Dan states, the compiler is free to ignore with a warning any pragmas that it doesn't understand."
    sorry Dan states - only IGNORE- but i said what compiler MUST WARNING ABOUT IT!!!

    YOUR POST IS SUPER POST :-))))
    THANK YOU !!!!!!

  • DEAR Patrick Noonan
    THANK YOU!!!

  • I should clarify that an implementation is free to ignore any pragmas that it doesn't recognise. It is not required to issue a warning.

    This implementation does issue warnings though for unrecognised pragmas. #pragma pack(1) seems to be special though.

    This might just be an omission from the documentation rather than a fault with the compiler though. It remains to be seen.