Messages in this thread | | | Date | Mon, 31 Jan 2022 18:55:26 +0100 | Subject | Test 73 Sig_trap fails on arm64 | From | Dmitry Vyukov <> |
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> On 18/01/2022 12:43, Leo Yan wrote: > > Hi Will, > > Can you kindly check below the question from Leo on this issue? > > You were cc'ed earlier in this thread so should be able to find more > context, if needed.
Hi Will, John,
I wonder if PSTATE.D flag can be used to resolve this (similar to x86's use of EFLAGS.RF)? I naively tried to do:
void OnSigtrap(int sig, siginfo_t* info, void* uctx) { auto& mctx = static_cast<ucontext_t*>(uctx)->uc_mcontext; mctx.pstate |= PSR_D_BIT; }
But then I got a SIGSEGV from kernel. But I wasn't able to track yet what part of the kernel did not like setting of D bit.
> Cheers, > John > > > On Tue, Jan 18, 2022 at 12:40:04PM +0100, Marco Elver wrote: > > > > [...] > > > >>> Both Arm and Arm64 platforms cannot support signal handler with > >>> breakpoint, please see the details in [1]. So I think we need > >>> something like below: > >>> > >>> static int test__sigtrap(struct test_suite *test __maybe_unused, int subtest __maybe_unused) > >>> { > >>> ... > >>> > >>> if (!BP_SIGNAL_IS_SUPPORTED) { > >>> pr_debug("Test not supported on this architecture"); > >>> return TEST_SKIP; > >>> } > >>> > >>> ... > >>> } > >>> > >>> Since we have defined BP_SIGNAL_IS_SUPPORTED, I think we can reuse it at > >>> here. > >>> > >>> [1]https://lore.kernel.org/lkml/157169993406.29376.12473771029179755767.tip-bot2@tip-bot2/ > >> Does this limitation also exist for address watchpoints? The sigtrap > >> test does not make use of instruction breakpoints, but instead just > >> sets up a watchpoint on access to a data address. > > Yes, after reading the code, the flow for either instrution breakpoint > > or watchpoint both use the single step [1], thus the signal handler will > > take the single step execution and lead to the infinite loop. > > > > I am not the best person to answer this question; @Will, could you > > confirm for this? Thanks! > > > > Leo > > > > [1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/kernel/hw_breakpoint.c
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