l4-hackers August 2022

l4-hackers@os.inf.tu-dresden.de

3 participants
3 discussions

Creating tasks and the l4_task_map function
by Paul Boddie 01 Oct '22

01 Oct '22

Hello, I finally got round to experimenting with L4Re again, but in attempting to investigate task creation, I seem to have some difficulties understanding the mechanism by which tasks are typically created and how the l4_task_map function might be used in the process. After looking at lots of different files in the L4Re distribution, my understanding of the basic mechanism is as follows: 1. Some memory is reserved for the UTCB of a new task, perhaps using the l4re_ma_alloc_align function (or equivalent) to obtain a dataspace. 2. A task is created using l4_factory_create_task, indicating the UTCB flexpage, with this being defined as... l4_factory_create_task(l4re_env()->factory, new_task, l4_fpage(utcb_start, utcb_log2size, L4_FPAGE_RW)) 3. A thread is created using l4_factory_create_thread. l4_factory_create_thread(l4re_env()->factory, new_thread) 4. The thread attributes are set using the l4_thread_control API. 5. The l4_thread_ex_regs function is used to set the instruction pointer (program counter) and stack pointer of the thread. 6. The l4_scheduler_run_thread function is used to initiate the thread. The expectation is that the thread will immediately fault because there is no memory mapped at the instruction pointer location. However, it seems to me that it should be possible to use l4_task_map to make a memory region available within the task's address space, although I don't ever see this function used in L4Re for anything. (The C++ API makes it difficult to perform ad-hoc searches for such low-level primitives, in my view, so perhaps I am missing use of the equivalent methods.) Tentatively, I would imagine that something like this might work: l4_task_map(new_task, L4RE_THIS_TASK_CAP, l4_fpage(program_start, program_log2size, L4_FPAGE_RX), task_program_start) Here, the program payload would be loaded into the creating task at program_start, but the new task would be receiving the payload at task_program_start, with the configured instruction pointer location occurring within the receive window (after task_program_start, in other words). There are, of course, many other considerations around creating tasks, which I have noted from looking at the different packages (libloader, l4re_kernel, moe, ned), and I am aware that a few other things need to be done to start a task such as... * Defining capability selectors and mapping appropriate capabilities to the new task. * Creating a stack for the task and populating it with arguments and environment information. * Defining a suitable pager and exception handler, with this usually being provided by the l4re binary, as I understand it. Also, when actually dealing with program loading generally, I realise that the ELF binary needs to be interpreted and the appropriate regions associated with different parts of memory, this typically being handled by the region mapper/ manager in L4Re. And there is also the matter of dynamic library loading. But here, I am just attempting to establish the basic mechanism when a task starts up. Unfortunately, the only discussion I found was this (after some initial discussion about a related topic): http://os.inf.tu-dresden.de/pipermail/l4-hackers/2014/015366.html There are various examples in Subversion (maybe somewhere in the Git repositories, too) that create tasks or threads, but I don't find them particularly helpful, apparently being oriented towards very specific applications. A previous example was referenced in the above thread for the older L4Env system (or maybe an even earlier system): http://os.inf.tu-dresden.de/pipermail/l4-hackers/2000/000384.html As for why I would be wondering about such things - a question inevitably asked in the first thread referenced above - I firstly want to be able to understand the mechanism involved, but I also want to be able to integrate work I have been doing on file paging into task creation. Although I can probably do this by customising the "app model" normally used by the different loaders, it seems that I would need to construct an alternative l4re binary, which is rather cumbersome and perhaps a weakness of the abstractions that are provided, these being rather oriented towards obtaining dataspaces via the namespace API which I don't want to have to support in my filesystem. In any case, I wonder if there are any resources that describe the use of l4_task_map and the details of the program environment within tasks. Paul

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NXP LX2160 Uboot Fail
by rib0327 11 Sep '22

11 Sep '22

Hi, I am currently trying to get the L4Re running on the NXP LX2160 with U-Boot. When I try to load a .uimage I get the following error message: FDT and ATAGS support not compiled in Thank you in advance for your help.

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Problem with newest Git-Version (RPi4)
by rib0327 28 Aug '22

28 Aug '22

Hello everyone, We have a question regarding the newest Kernel version available on Git (current date: 11.08.2022). We are working on an application and have come across a problem. In a previous Git version of the Kernel we had no problem building the .uimage file; however, with the newest update we found out that the .uimage file cannot be built. Here the working version (older one): Buildung local Project exampleApp [ExampleApp_Git] ... Compiling src/main.o [ExampleApp_Git] ==> Linking exampleApp [ExampleApp_Git] ==> exampleApp built [ExampleApp_Git] ==> Installing exampleApp to local build-tree Building L4Re uimage with Application exampleApp make[1]: Entering directory '/home/dev/L4Re_Git/l4' Building entry "exampleApp". Merging images: mod00: /home/dev/L4Re_Git/build-fiasco//fiasco [436kB] mod01: /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a/l4f/sigma0 [36kBBuildung local Project exampleApp [ExampleApp_Git] ... Compiling src/main.o [ExampleApp_Git] ==> Linking exampleApp [ExampleApp_Git] ==> exampleApp built [ExampleApp_Git] ==> Installing exampleApp to local build-tree Building L4Re uimage with Application exampleApp make[1]: Entering directory '/home/dev/L4Re_Git/l4' Building entry "exampleApp". Merging images: mod00: /home/dev/L4Re_Git/build-fiasco//fiasco [436kB] mod01: /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a/l4f/sigma0 [36kB] mod02: /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a/l4f/moe [226kB] mod03: /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a/l4f/l4re [117kB] mod04: /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a/l4f/exampleApp [174kB] [bootstrap] ... Generating bootstrap.ld [bootstrap] ... Compiling startup.o [bootstrap] ==> Linking bootstrap.elf [bootstrap] ==> Image post-processing bootstrap.elf [bootstrap] ==> bootstrap.elf built ==> Installing bootstrap.elf in image directory ==> Installing bootstrap_exampleApp in image directory ==> Installing bootstrap_exampleApp.elf in image directory [bootstrap] ... Generating bootstrap.raw ==> Installing bootstrap.raw in image directory ==> Installing bootstrap_exampleApp.raw in image directory [bootstrap] ... Generating bootstrap.uimage Image Name: L4 Image #3 Created: Thu Aug 11 09:11:24 2022 Image Type: AArch64 Linux Kernel Image (uncompressed) Data Size: 1099688 Bytes = 1073.91 KiB = 1.05 MiB Load Address: 01000000 Entry Point: 01000000 ==> Installing bootstrap.uimage in image directory ==> Installing bootstrap_exampleApp.uimage in image directory Image size(s) in bytes: bootstrap_exampleApp.elf: 1534296 bootstrap.raw: 1099688 bootstrap.uimage: 1099752 Start address: 0x1000000 --> Build-Nr: 3 [bootstrap] ==> Installing bootstrap.elf to local build-tree [bootstrap] ==> Installing bootstrap_exampleApp to local build-tree [bootstrap] ==> Installing bootstrap_exampleApp.elf to local build-tree make[1]: Leaving directory '/home/dev/L4Re_Git/l4' DONE - bootstrap_exampleApp.uimage copied to /tftp/! ] mod02: /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a/l4f/moe [226kB] mod03: /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a/l4f/l4re [117kB] mod04: /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a/l4f/exampleApp [174kB] [bootstrap] ... Generating bootstrap.ld [bootstrap] ... Compiling startup.o [bootstrap] ==> Linking bootstrap.elf [bootstrap] ==> Image post-processing bootstrap.elf [bootstrap] ==> bootstrap.elf built ==> Installing bootstrap.elf in image directory ==> Installing bootstrap_exampleApp in image directory ==> Installing bootstrap_exampleApp.elf in image directory [bootstrap] ... Generating bootstrap.raw ==> Installing bootstrap.raw in image directory ==> Installing bootstrap_exampleApp.raw in image directory [bootstrap] ... Generating bootstrap.uimage Image Name: L4 Image #3 Created: Thu Aug 11 09:11:24 2022 Image Type: AArch64 Linux Kernel Image (uncompressed) Data Size: 1099688 Bytes = 1073.91 KiB = 1.05 MiB Load Address: 01000000 Entry Point: 01000000 ==> Installing bootstrap.uimage in image directory ==> Installing bootstrap_exampleApp.uimage in image directory Image size(s) in bytes: bootstrap_exampleApp.elf: 1534296 bootstrap.raw: 1099688 bootstrap.uimage: 1099752 Start address: 0x1000000 --> Build-Nr: 3 [bootstrap] ==> Installing bootstrap.elf to local build-tree [bootstrap] ==> Installing bootstrap_exampleApp to local build-tree [bootstrap] ==> Installing bootstrap_exampleApp.elf to local build-tree make[1]: Leaving directory '/home/dev/L4Re_Git/l4' DONE - bootstrap_exampleApp.uimage copied to /tftp/! And now the faulty one (latest version): Buildung local Project exampleApp [ExampleApp_Git] ==> Linking exampleApp aarch64-linux-gnu-ld: cannot find ./src/main.o: No such file or directory make[1]: *** [/home/dev/L4Re_Git/l4/mk/prog.mk:125: exampleApp] Error 1 make: *** [/home/dev/L4Re_Git/l4//mk/binary.inc:159: /home/dev/L4Re_Git/build-l4re/ext-pkg/home/dev/L4Re_Dev/ExampleApp_Git/OBJ-arm64_armv8a-l4f] Error 2 Building L4Re uimage with Application exampleApp make[1]: Entering directory '/home/dev/L4Re_Git/l4' Could not find 'exampleApp' within paths /home/dev/L4Re_Git/build-fiasco/ /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a /home/dev/L4Re_Git/build-l4re/bin/arm64_armv8a/l4f /home/dev/L4Re_Git/build-l4re/lib/arm64_armv8a /home/dev/L4Re_Git/build-l4re/lib/arm64_armv8a/l4f Processing of entry exampleApp in /home/dev/L4Re_Git/l4/conf/modules.list failed! make[3]: *** No rule to make target 'processing-of-module-list-failed', needed by 'mod.make.inc'. Stop. make[2]: *** [../../../../mk/binary.inc:159: /home/dev/L4Re_Git/build-l4re/pkg/bootstrap/server/src/OBJ-arm64_armv8a] Error 2 make[1]: *** [Makefile:544: uimage] Error 2 make[1]: Leaving directory '/home/dev/L4Re_Git/l4' make: *** [Makefile:6: do-all-make-goals] Error 2 cp: cannot stat '/home/dev/L4Re_Git/build-l4re/pkg/bootstrap/server/src/OBJ-arm64_armv8a/bootstrap_exampleApp.uimage': No such file or directory DONE - bootstrap_exampleApp.uimage copied to /tftp/! This does not happen if we create the image of ‘hello’. The problem is that the main.c file in the exampleApp does not get compiled before being linked à aarch64-linux-gnu-ld: cannot find ./src/main.o: No such file or directory. Everything was added correctly in modules.list. Does it depend on the newest update or did we make a mistake somewhere? In the attachment you will also find the build_all.sh file we used to build the image and also the Makefile for exampleApp. Thank you in advance for your help. Many regards, Mauro, Ricardo

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l4-hackers August 2022