Uninitialized variables is getting assigned to DATA section instead of BSS section in ARM Compiler 6.6

I assume that you mean uninitialized global variables here. Such a variable is placed in .bss by the compiler in the object file. The linker is very flexible, so maybe you have inadvertently asked it to place bss data from object files into general data sections in the executable image? With fromelf -s you should be able to see where it goes wrong (object or image) and which symbol is placed in which section, and check the section type/flags to see if this is a .bss (SHT_NOBITS is set) or a .data (SHT_PROGBITS and SHF_WRITE are set). Hope this helps.

Hello Christof,

Thank you for the info.

Please find the detailed info about my query.

Case 1:

unsigned char __attribute__((section(".myregion"))) myData[0x2000];

Map file:

Base Addr    Size         Type   Attr      Idx    E Section Name        Object

0x20000000   0x00002000   Data   RW         6699    .myregion           myFile.a(myFile1.obj)

Case 2:

unsigned char __attribute__((section(".bss.myregion"))) myData[0x2000];

Map file:

Base Addr    Size         Type   Attr      Idx    E Section Name        Object

0x20000000   0x00002000   Zero   RW         6699    .myregion           myFile.a(myFile1.obj)

In Case 1, why is the section Type set to "Data"?

Can I have any other way of setting a particular section Type to "Zero" other than using .bss.<section_name>

• the section attribute as you already use (you can use macros to add the prefix".bss." rather than writing it down all the time)
• #pragma arm section is another way to control the sections, I've never used it but you can read the documentation at https://developer.arm.com/docs/dui0774/h/compiler-specific-pragmas/pragma-clang-section

The latter seems to be what you want:

// set bss section to .myRegion
#pragma clang section bss=".myRegion"
unsigned char myData[0x2000];
// reset bss section to original
#pragma clang section bss=""