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Position Independent Code with RTX startup file

Tom Cooper

I want to compile my project to be PI (it is an RTX app running C code on STM32L1xx). For target options, I check "Make RO Sections PI" in the Linker tab with no scatter file or misc controls. In the C/C++ and Asm tabs, I check "RO PI" and add "--apcs=/fpic" to misc controls.

Upon cleaning/rebuilding the target, I get no compiler warnings or errors, but the linker throws hundreds of warnings and errors for all object files, with these 3 codes:
L6412W
L6248E
L6285E

I've obviously looked up the meaning of these error codes, but I'm not sure what to do about it. I've read infocenter.arm.com/.../index.jsp but I can safely assume I'm not doing this in every object file; I suspect it's something more fundamental to the target options. Even my Startup.s file has these errors and I copied it from STM. Any ideas?

Some examples of warning and error messages are:

.\obj\Project_Pic.axf: Warning: L6412W: Disabling merging for mytask.o(.conststring), unsupported relocation R_ARM_REL32 from mytask.o(.text)

.\obj\Project_Pic.axf: Error: L6248E: startup.o(RESET) in PI region 'ER_RO' cannot have address type relocation to Reset_Handler in PI region 'ER_RO'.
.\obj\Project_Pic.axf: Error: L6248E: startup.o(RESET) in PI region 'ER_RO' cannot have address type relocation to NMI_Handler in PI region 'ER_RO'.
.\obj\Project_Pic.axf: Error: L6248E: startup.o(RESET) in PI region 'ER_RO' cannot have address type relocation to HardFault_Handler in PI region 'ER_RO'.

.\obj\Project_Pic.axf: Error: L6248E: params.o(.text) in PI region 'ER_RO' cannot have offset type relocation to m_p_MyParams in ABSOLUTE region 'ER_RW'.
.\obj\Project_Pic.axf: Error: L6248E: routing.o(.text) in PI region 'ER_RO' cannot have offset type relocation to m_MyMutex in ABSOLUTE region 'ER_ZI'.
.\obj\Project_Pic.axf: Error: L6248E: params.o(.data) in ABSOLUTE region 'ER_RW' cannot have address/offset type relocation to GetMyParam in PI region 'ER_RO'.

.\obj\Project_Pic.axf: Error: L6285E: Non-relocatable Load region LR_1 contains R-Type dynamic relocations. First R-Type dynamic relocation found in startup.o(RESET) at offset 0x4.

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  • 0 in reply to Westonsupermare Pier

    One of your other choices could be to modify the scatter file so that it builds a load region at the bottom of RAM, and puts the vector table in there. The C start up code can then copy that data in, or you can move it manually in main()

    But you're still going to need to break this into two pieces so the "App" portion is separate from the "Loader" portion which HAS to manage the requirements of the Cortex-M3 to have a vector table with fixed addresses for the initial stack, and program counter.

    May be you want to go look at how things are done with the Cortex-M0, where you can't relocate the vector table. Look at the IAP (In Application Programming) type examples. Look also how ARM7/9 and 68000 part used to deal with the dilemma of booting a ROM and relocating vectors into RAM, and relative branching.

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  • 0 in reply to Westonsupermare Pier

    One of your other choices could be to modify the scatter file so that it builds a load region at the bottom of RAM, and puts the vector table in there. The C start up code can then copy that data in, or you can move it manually in main()

    But you're still going to need to break this into two pieces so the "App" portion is separate from the "Loader" portion which HAS to manage the requirements of the Cortex-M3 to have a vector table with fixed addresses for the initial stack, and program counter.

    May be you want to go look at how things are done with the Cortex-M0, where you can't relocate the vector table. Look at the IAP (In Application Programming) type examples. Look also how ARM7/9 and 68000 part used to deal with the dilemma of booting a ROM and relocating vectors into RAM, and relative branching.

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