Sorry. Forgot to include link to v2. Here it is: https://lore.kernel.org/linux-arm-kernel/20210402032404.47239-1-madvenka@xxxxxxxxxxxxxxxxxxx/ Thanks! Madhavan On 4/19/21 1:16 PM, Madhavan T. Venkataraman wrote: > CCing Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> on request. > > Pasha, > > This is v2. v1 is here: > > https://lore.kernel.org/linux-arm-kernel/20210324184607.120948-1-madvenka@xxxxxxxxxxxxxxxxxxx/ > > Thanks! > > Madhavan > > On 4/1/21 10:24 PM, madvenka@xxxxxxxxxxxxxxxxxxx wrote: >> From: "Madhavan T. Venkataraman" <madvenka@xxxxxxxxxxxxxxxxxxx> >> >> Reliable stacktracing requires that we identify when a stacktrace is >> terminated early. We can do this by ensuring all tasks have a final >> frame record at a known location on their task stack, and checking >> that this is the final frame record in the chain. >> >> All tasks have a pt_regs structure right after the task stack in the stack >> page. The pt_regs structure contains a stackframe field. Make this stackframe >> field the final frame in the task stack so all stack traces end at a fixed >> stack offset. >> >> For kernel tasks, this is simple to understand. For user tasks, there is >> some extra detail. User tasks get created via fork() et al. Once they return >> from fork, they enter the kernel only on an EL0 exception. In arm64, >> system calls are also EL0 exceptions. >> >> The EL0 exception handler uses the task pt_regs mentioned above to save >> register state and call different exception functions. All stack traces >> from EL0 exception code must end at the pt_regs. So, make pt_regs->stackframe >> the final frame in the EL0 exception stack. >> >> To summarize, task_pt_regs(task)->stackframe will always be the final frame >> in a stack trace. >> >> Sample stack traces >> =================== >> >> The final frame for the idle tasks is different from v1. The rest of the >> stack traces are the same. >> >> Primary CPU's idle task (changed from v1) >> ======================= >> >> [ 0.022365] arch_stack_walk+0x0/0xd0 >> [ 0.022376] callfd_stack+0x30/0x60 >> [ 0.022387] rest_init+0xd8/0xf8 >> [ 0.022397] arch_call_rest_init+0x18/0x24 >> [ 0.022411] start_kernel+0x5b8/0x5f4 >> [ 0.022424] __primary_switched+0xa8/0xac >> >> Secondary CPU's idle task (changed from v1) >> ========================= >> >> [ 0.022484] arch_stack_walk+0x0/0xd0 >> [ 0.022494] callfd_stack+0x30/0x60 >> [ 0.022502] secondary_start_kernel+0x188/0x1e0 >> [ 0.022513] __secondary_switched+0x80/0x84 >> >> --- >> Changelog: >> >> v1 >> - Set up task_pt_regs(current)->stackframe as the final frame >> when a new task is initialized in copy_thread(). >> >> - Create pt_regs for the idle tasks and set up pt_regs->stackframe >> as the final frame for the idle tasks. >> >> - Set up task_pt_regs(current)->stackframe as the final frame in >> the EL0 exception handler so the EL0 exception stack trace ends >> there. >> >> - Terminate the stack trace successfully in unwind_frame() when >> the FP reaches task_pt_regs(current)->stackframe. >> >> - The stack traces (above) in the kernel will terminate at the >> correct place. Debuggers may show an extra record 0x0 at the end >> for pt_regs->stackframe. That said, I did not see that extra frame >> when I did stack traces using gdb. >> v2 >> - Changed some wordings as suggested by Mark Rutland. >> >> - Removed the synthetic return PC for idle tasks. Changed the >> branches to start_kernel() and secondary_start_kernel() to >> calls so that they will have a proper return PC. >> >> Madhavan T. Venkataraman (1): >> arm64: Implement stack trace termination record >> >> arch/arm64/kernel/entry.S | 8 +++++--- >> arch/arm64/kernel/head.S | 29 +++++++++++++++++++++++------ >> arch/arm64/kernel/process.c | 5 +++++ >> arch/arm64/kernel/stacktrace.c | 10 +++++----- >> 4 files changed, 38 insertions(+), 14 deletions(-) >> >> >> base-commit: 0d02ec6b3136c73c09e7859f0d0e4e2c4c07b49b >>
