Having defines in linker script for memory origin and length

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MEMORY
{
    RAM (rxai!w) :                  ORIGIN = 0x80000000 LENGTH = 34K
}

Lets say I have a section in linker script like above. can i have a define for 0x80000000 and 34K. I want it to look like,

MEMORY
{
    RAM (rxai!w) :                  ORIGIN = RAM_ORIGIN LENGTH = RAM_LENGTH
}

So my question how to put this define in linker script? I have a script that auto generates the linker script and the defines will be different every time.

gcc
linker
linker-scripts
linker-flags
asked on Stack Overflow Jan 30, 2019 by Thomas

2 Answers

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I figured that having the defines a different file like common.ld in the following format,

RAM_ORIGIN = 0x80000000;
RAM_LENGTH = 34K;

works. But this common.ld could not be included directly in the linker script using 'INCLUDE'. If i pass it in the command line as -Wl,common.ld then it works.

answered on Stack Overflow Feb 5, 2019 by Thomas
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I have solved this using the C preprocessor cpp.

My linker scripts contain 'variables' that can be 'filled' from the Makefile invoking cpp for the actuals:

LDCSRC=script.lk.in
LDCDILE=script.lk

$(LDCFILE): $(LDCSRC)
        $(Q)echo CPP $<
        $(Q)$(CPP) $(INCLUDE) -DOBJDIR=$(1)/objs -P -DFORMAT_ELF=$(FORMAT_ELF) -D$$(MACHINE) $$< -o $$@

the linker script itself can then be 'beefed up' with cpp macros as well:

#ifdef COMPILE_RAM
#define ROMFLAGS    WX
#else
#define ROMFLAGS    RX
#endif /* COMPILE_RAM */

MEMORY
{
    _rom (ROMFLAGS) : ORIGIN = TARGET_ADDRESS, LENGTH = 0x00100000

In this example, the linker script even #includes a C header file (not shown) to define TARGET_ADDRESS to ensure we have the same definition in the code and in the linker script. You just need to make sure this *.h file does not contain statements that disturb the linker (should only contain preprocessor definitions).

answered on Stack Overflow Feb 7, 2019 by mfro • edited Feb 7, 2019 by mfro

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