From mboxrd@z Thu Jan 1 00:00:00 1970 From: gerg@snapgear.com (Greg Ungerer) Date: Tue, 8 May 2012 14:50:06 +1000 Subject: [uClinux-dev] Running linux with mmu disabled on arm (AT91). In-Reply-To: <4FA00040.8000207@fnac.net> References: <4FA00040.8000207@fnac.net> Message-ID: <4FA8A5FE.3080709@snapgear.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Paul, On 02/05/12 01:24, Paul Chavent wrote: > I'd like to try linux on an AT91SAM9G20 (i have a linuxstamp board), with MMU disabled (the Hyok-Sung Choi& Hee-Chul Yun paper demonstrate that it could be possible). > > All the code seems to be present in the kernel... > So i would like to share my experience. > > (1) I had to make two little changes in the kernel code : > - I'm not able to change the REMAP_VECTOR_TO_DRAM. I have submitted the problem to the kbuild mailing list (http://www.spinics.net/lists/linux-kbuild/msg06153.html). Odd. Is it because DRAM_BASE is a numerical value? > - The soc_detect code that init the at91_soc_initdata structure is never called. Later this structure is used unitialized. > I'm currently using the joined patch as a workaround. Someone can review it please ? It looks ok to me. > (2) I used to run the module with a "classic system" based on linux + eglibc, and i needed only one toolchain (arm-xxx-linux-gnueabi) for the kernel and the userspace apps. > I found that for the nommu case i wasn't able to build the kernel with the userspace toolchain. > So I had to build 2 toolchain, based on binutils 2.22, gcc 4.7, uclibc 0.9.33.1 and linux 3.2.14 : > - an arm-xxx-eabi toolchain for the kernel > - an arm-xxx-uclinux-uclibceabi for the userspace apps > Do you confirm that it is not possible to compile the kernel with arm-xxx-uclinux-uclibceabi ? Or, may i have misconfigured the toolchain (i join the toolchain build procedure) ? I build non-mmu ARM systems with the same toolchain. What was the failure condition when building the kernel with the arm-yyy-uclinux-uclibceabi tool chain? > (3) The arm-xxx-uclinux-uclibceabi with elf2flt seems to produce running bins only if it is build with the uClibc DOPIC not set. > Is it required to disable DOPIC ? > Moreover, i can't run bins produced with a arm-xxx-linux-uclibceabi toolchain and -Wl,-elf2flt (not uclinux one). Is it the expected behavior ? Is it actually producing a FLAT format binary? Maybe it is silently ignoring the "-Wl,-elf2flt". > (4) The elf2flt needs to be updated to be aware of the exidx section, and some reloc types. I join the patch i currently use. You shouldn't include a whole new elft2flt.ld for this. It is generated (via autoconf) from the elf2flt.ld.in file. You should add your new exidx section to that. If you want to generate a new patch with doing it that way I can add it to the elf2flt CVS on uclinux.org. > Given these observations, i've been able to run a linux with an hello world as the /init process. > > My next tests will be to run threaded programs, c++ programs, then busybox. A good start at least. Regards Greg -- ------------------------------------------------------------------------ Greg Ungerer -- Principal Engineer EMAIL: gerg at snapgear.com SnapGear Group, McAfee PHONE: +61 7 3435 2888 8 Gardner Close FAX: +61 7 3217 5323 Milton, QLD, 4064, Australia WEB: http://www.SnapGear.com