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GCC elf generation with non-aligned sections vs linker configuration

Tilen

I have observed that GCC generates strange "Program header tables" in the output elf file when flash configuration of the linker script is not 16-bit aligned.

An example of the linker script that doesn't work well. Address of flash is set to non 16-bit alignment as you can see it has 0xC000 offset in the lower bytes.

MEMORY
{
 RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 64K
 FLASH (rx) : ORIGIN = 0x0800C000, LENGTH = 256K
}

When we generate elf file like this

Program header tables
Type                Offset              VAddr               PAddr     
PT_LOAD             0x00000000          0x08000000          0x08000000
PT_LOAD             0x00010000          0x20000000          0x08001FD4
PT_LOAD             0x0000002C          0x2000002C          0x08001FE0

Why it is not aligned to the start of actual flash memory, that being 0x0800C000 and why are 2 lower bytes masked out and set to 0?

If linker script is like that (so now going to 0x08010000) then it works well:

MEMORY
{
 RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 64K
 FLASH (rx) : ORIGIN = 0x08010000, LENGTH = 256K
}
Program header tables
Type                Offset              VAddr               PAddr     
PT_LOAD             0x00000000          0x08010000          0x08000000
PT_LOAD             0x00010000          0x20000000          0x08001FD4
PT_LOAD             0x0000002C          0x2000002C          0x08001FE0


Then again one that is strange, see lower 2 bytes are not all zeros.

MEMORY
{
 RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 64K
 FLASH (rx) : ORIGIN = 0x0801B000, LENGTH = 256K
}
Program header tables
Type                Offset              VAddr               PAddr     
PT_LOAD             0x00000000          0x08010000          0x08000000
PT_LOAD             0x00010000          0x20000000          0x08001FD4
PT_LOAD             0x0000002C          0x2000002C          0x08001FE0

What is the catch behind and why is GCC masking out lower 2 bytes?

Thanks in advance, Tilen

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