issueMDK4.10 compile problem....hple me

hi everyone,
i will to see compile file uart.txt and iotest.txt,the result are blow:

uart.txt

 AREA ||.data||, DATA, ALIGN=2

                  UART0TxEmpty
000000  03                DCB      0x01
                  UART1TxEmpty
000001  010000            DCB      0x01,0x00,0x00
                  UART0Count
                          DCD      0x00000000
                  UART1Count
                          DCD      0x00000000
                  UART0Status
                          DCD      0x00000000
                  UART1Status
                          DCD      0x00000000

iotest.txt

000042  0000              DCW      0x0000
                  |L1.68|
                          DCD      UART0Count
                  |L1.72|
                          DCD      0x4000c000
                  |L1.76|
                          DCD      UART0Buffer
                  |L1.80|
                          DCD      Teststring

                          AREA ||.data||, DATA, ALIGN=0

                  Teststring
000000  01020304          DCB      0x31,0x32,0x33,0x34
000004  35363738          DCB      0x35,0x36,0x37,0x38
000008  3930              DCB      0x39,0x30

the compiler seem to initialize global variables, but in the debugger did not.in the debugger i to saw symbols,that shown UART0Count value was 0x20485231 and Teststring was 0xd0,0x42,...this value was memory(ram) value,and then i used memset to clean ram(start:0x10000000 size:512byte data:0x0),i to saw UART0Count and Teststring value were 0x00000000,so compiler did not initial,but compile file shown the value were correct.did i setting wrong?

i solve the problem,because i modify IMPORT __main to IMPORT main,but i do not understand why modify this __main to main,will cause global variables not initial.anyone can tell me thank..

When you power up the processor, SRAM memory will hold random (or at least semi-random) contents.

So the processor needs to initialize the RAM. It does that by clearing all memory regions that holds zero-initialized variables (global variables that haven't been given any initial value explicitly by you). And in the flash, it has a copy of the initial values for all global variables that you have specified an initial value for.

But this clearing/copying is performed by the startup code, i.e. code run before the processor reaches your main() function. If you do play with the startup code, so you don't run all the initialization functions inside the runtime library, you may still get to main(), but can't have any expectations on memory contents, or that internal structures inside the RTL have been correctly initialized.

So you have to realize that main _main or __main are completely different symbols. Your main() normally gets the external linkage name _main, i.e. with a single underscore added. Symbols with two underscores are reserved for the compiler/RTL, meaning you should not create own symbols that starts with a single '_' character. Also, linkage symbols without any leading underscore are also belonging to a namespace your C program can't reach (since the C compiler adds a single underscore to your symbol names) and hence a symbol "owned" by the compiler/RTL vendor.

In the end, it is your responsibility to make sure that the startup code does call the required RTL initialization functions and let them call your main(), instead of trying to get the startup file to get directly to your main().

Or more specifically - if your startup file gets directly to your main(): who do you think will then distribute initialized values to your ZI and RW variables? The processor itself?

i modify IMPORT __main to IMPORT main,but i do not understand

Then what on earth made you do it? On what basis did you believe you knew better than the authors of that startup code how to start the main function?

thank Per Westermark reply^^,i understand you say.thank again.
and i accidentally changed it,so i debuged so long~~~~~but i learned this konwleage, thank you