Strange LMA/VMA behavior with regions

[Sebastian Huber <sebastian.huber@embedded-brains.de>]

Hi,

I have to write a custom linker script to distribute various output sections to
various physical memory regions (for embedded devices).  I have this linker
SECTIONS part:

	.jcr : {
		KEEP (*(.jcr))
	} > REGION AT > REGION
	.rodata : {
		*(.rodata .rodata.* .gnu.linkonce.r.*)
	} > REGION AT > REGION

The .rodata section has a section alignment of 8 (the alignment depends on the
application, it may be higher).  Now suppose that the .jcr end is not 8 bytes
aligned.  We may have this:

.jcr            0x00000000800198b0        0x4
 *(.jcr)
 .jcr           0x00000000800198b0        0x0 crtbegin.o
 .jcr           0x00000000800198b0        0x4 crtend.o

.rodata         0x00000000800198b8     0x2ba8 load address 0x00000000800198b4
 *(.rodata .rodata.* .gnu.linkonce.r.*)

This is pretty bad, since this introduces a 4 byte offset in the .rodata
section.  If I use this SECTIONS part:

	.jcr : {
		KEEP (*(.jcr))
	} > REGION AT > REGION
	.rodata : ALIGN (8) {
		*(.rodata .rodata.* .gnu.linkonce.r.*)
	} > REGION AT > REGION

We get this:

.jcr            0x00000000800198b0        0x4
 *(.jcr)
 .jcr           0x00000000800198b0        0x0 crtbegin.o
 .jcr           0x00000000800198b0        0x4 crtend.o

.rodata         0x00000000800198b8     0x2ba8
 *(.rodata .rodata.* .gnu.linkonce.r.*)

Unfortunately the section alignment is unknown in advance, so .rodata : ALIGN
(ALIGNOF(.rodata)) { ... } is not possible.  Please observe that LMA==VMA in
.jcr.  Let OFFSET := LMA - VMA.  I think that LD should not introduce an OFFSET
!= 0 due to alignment constraints if the load and runtime region are equal.

Have a nice day!

-- 
Sebastian Huber, embedded brains GmbH

Address : Obere Lagerstr. 30, D-82178 Puchheim, Germany
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