On Wed, Apr 20, 2011 at 11:56 PM, Aneesh V aneesh@ti.com wrote:
Hi Simon, Wolfgang,
On Thursday 21 April 2011 12:04 AM, Simon Glass wrote:
On Fri, Mar 25, 2011 at 11:35 AM, Albert ARIBAUDalbert.aribaud@free.fr wrote:
Le 25/03/2011 17:12, Aneesh V a écrit :
Another problem I have with relocation is that it makes debugging with JTAG debugers more difficult. The addresses of symbols in the ELF target are no longer valid. Of course, you can load the symbols at an offset from the original location. But one has to first enable debug prints, find the relocation offset, use it while loading the symbols before you can do source level debugging.
Actually you don't need recompiling: simply set a breakpoint at the entry of relocate_code and once you hit the bp, look up r2: it contains the destination. If you want the offset rather than the absolute address, set the breakpoint right after the 'sub r9, r6, r0' round line 222: r9 will then give you the offset. Unload the current symbols, reload the symbols with the relevant offset, and there you go.
I would like to revisit this thread. I'm not sure how other people do development in U-Boot but I like to use an ICE and a source-level debugger for any significant effort. I think it should be possible to use a JTAG debugging just by loading the u-boot ELF file and running.
With this patch (or something similar) this is possible. Without it, it is painful.
To be clear, we are not talking here about creating a platform that doesn't use relocation, just that for development purposes it is convenient to be able to disable it.
Actually, I am not even sure why relocation shouldn't be disabled in my platform for good. It may be useful to have things such as the frame buffer at the end of available memory. But, IMHO, that can still be done without relocating u-boot. That's what the patch does.Am I missing something?
Well relocation does remove a lot of this ad-hoc positioning of things at compile time. I think it is desirable. My point is that it is not engineer-friendly during development, and we should have an easy way to disable it for debugging / JTAG purposes.
Regards, Simon
Looking at the December thread http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/88067/focus=88262
Aneesh:
Shouldn't we provide a CONFIG option by which users can disable Elf relocation?
Wolfgang:
Why should we? It would just make the code even more complicated, and require a lot of additional test cases.
From what I can see this is a new CONFIG option, two ifdefs in the board.c file, and optionally disabling the -pie position-independent executable option to reduce size. It is pretty trivial:
arch/arm/config.mk | 2 ++ arch/arm/lib/board.c | 5 +++++ 2 files changed, 7 insertions(+), 0 deletions(-)
Regards, Simon
Amicalement,
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