b19c9dea3e
The arm kernel stack unwinder has apparently never been able to unwind when the path of execution leads through a kernel module. There was code that tried to handle modules by looking for the unwind data in them, but it did so by trying to find symbols which have never existed in arm kernel modules. That caused the unwind code to panic, and because part of panic handling calls into the unwind code, that just created a recursion loop. Locating the unwind data in a loaded module requires accessing the Elf section headers to find the SHT_ARM_EXIDX section. For preloaded modules those headers are present in a metadata blob. For dynamically loaded modules, the headers are present only while the loading is in progress; the memory is freed once the module is ready to use. For that reason, there is new code in kern/link_elf.c, wrapped in #ifdef __arm__, to extract the unwind info while the headers are loaded. The values are saved into new fields in the linker_file structure which are also conditional on __arm__. In arm/unwind.c there is new code to locally cache the per-module info needed to find the unwind tables. The local cache is crafted for lockless read access, because the unwind code often needs to run in context where sleeping is not allowed. A large comment block describes the local cache list, so I won't repeat it all here.
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