fa2cbdc7cb
2 Commits
| Author | SHA1 | Message | Date | |
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Alexander Boettcher
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54ed373468 |
NOVA: translate item patch, issue #268
Unfortunately, another kernel patch is required for Genode/NOVA to get rid of global unique ids for objects (issue #268). Kernel patch: If a translate of a object capability item inside the same PD (receiver/sender in same PD) is not successful then he very same item is returned instead of the null item. Genode: Some code in Genode try to map/translate the "root" (the first instance of a) object capability within the same PD. The translate fails since it is the first cap and was not delegated beforehand. Instead the cap gets mapped to a new capability index due to xlt_rcv kernel item patch. The new local object capability index is used to lookup manged objects in lists, which however fails because the object is only known by the original object capability index. Unfortunately, this happens not only once. Below one example trace and description is attached. There are several possible solutions possible: * Find all places in Genode and replace normal function calls between objects with IPC calls, such that all capabilities can be translated during IPC. ** Time consuming to find all spots ** Rather platform specific issue requires re-adjustments in generic Genode code ** Not trivial to ever remember this fact during development of new components [other platforms have not such a issue, however have global object ids] ** Neither good in terms of performance. * Use some special system call to the kernel to be able to translate a given capability index as long until you find the requested original index. (Obviously ... no comment). * Kernel patch as this one. * <your proposal> Example trace + code description showing the behavior above: int main(): --- create local services --- int main(): --- start init --- [0] DEL OBJ PD:0xc000aa80->0xc000aa80 SB:0x000000aa RB:0x000000ac O:0x00 A:0x1f int main(): transferred 42 MB to init [0] DEL OBJ PD:0xc000aa80->0xc000aa80 SB:0x00000120 RB:0x0000013c O:0x00 A:0x1f [0] DEL OBJ PD:0xc000aa80->0xc000aa80 SB:0x0000016c RB:0x00000168 O:0x00 A:0x1f Setup ELF failed [0] XLT OBJ PD:0xc000aa80->0xc000aa80 SB:0x00000168 RB:0x0000016c O:0x00 unknown exception? int main(): --- init created, waiting for exit condition --- thread - file - line - text ------------------------------------------------------------------------------- thread A - [ 0] - 228 - new Core_child(... rom_session.dataspace() ...) thread A - [ 1] - 27 - IPC call - ask for dataspace cap thread B - [ 2] - 49 - function - return dataspace cap index 0x120 thread A - [ 1] - 27 - IPC returned - map 0x120 -> 0x13c, translate failed thread A - ... thread A - [ 3] - 231 - call _setup_elf() thread A - [ 3] - 60 - call env->rm_session()->attach() thread A - [ 4] - 35 - do dataspace object lookup (0x13c) thread A - [ 4] - 36 - lookup failed (object known as 0x120), throw Exception thread A - [ 3] - 61 - catch Exception -> return error code "0" thread A - [ 3] - 233 - "Setup ELF failed" - because error code "0" File legend: [0] base/src/core/main.cc [1] base/include/rom_session/client.h [2] base-nova/src/core/include/core_rm_session.h [3] base/src/base/process/process.cc [4] base-nova/src/core/core_rm_session.cc |
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Alexander Boettcher
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2b161b7aff |
NOVA: use translate feature of kernel, issue #268
Kernel patch: Introduce a transfer item type to express that a cap should be translated and if this fails to map it instead. It would be possible without this combined transfer item type however with additional overhead. In this case Genode/NOVA would have to map and translate all caps used as parameter in IPC. It would look like this: * If the map and translation succeed, the cap at the new cap index would have to be revoked. Then the translated cap index can be used. * If the map succeeds and the translation fails then the mapped cap index can be used. * It would become complicated when multiple caps are mapped and translated and only some of the translation succeed. In such cases Genode would have to figure out the right relation of translated/mapped and not translated/mapped caps. It would require to make some assumption about the order how translated/mapped caps are reported at the UTCB by the kernel. All the points above lead to the decision to create a separate transfer item type for that. Genode: Most the times the translation succeeds, mapping of caps happens either seldom. This takes now a bit the pressure of not enough aligned receive cap windows as described in issue #247. The patch mainly adds adjustments to handle the translated and mapped caps correctly especially during freeing of the receive window (don't free translated cap indexes). Fixes #268 |