Hi Fabrizio,
The issue with -O0 is that the kernels idle thread (idle_thread) on x86 is not
given a stack and at -O0 the -fomit-frame-pointer optimization is not enabled
(it is enabled at -O1), resulting in idle_thread attempting to use a stack.
Using -O0 is therefore not recommended as you need to also (on x86 at least)
add at least the -fomit-frame-pointer option to the kernel flags list.
Adrian
On Fri 25-May-2018 7:34 AM, Fabrizio Bertocci wrote:
> Hi,
> After hours of debugging I have discovered a quite nasty issue where
> seL4_Wait() crash if I build the kernel without optimization (gcc option
> -O0) on a pc99 tested with qemu.
>
> How to reproduce: Just create an endpoint (from a vka) and call
> seL4_Wait(). The simplest reproducer can be obtained from the hello-2
> tutorial:
> - Copy the main.c from the solution directory in the apps/hello-2/src/main.c
>
> - Add the following codes right after the creation of vka (TASK 5, approx
> line 150):
> {
> printf("WAITING----------------------------------------------\n");
> seL4_Word myBadge;
> vka_object_t ep_object = {0};
> error = vka_alloc_endpoint(&vka, &ep_object);
> ZF_LOGF_IFERR(error, "Failed to allocate new endpoint object.\n");
> seL4_Wait(ep_object.cptr, &myBadge);
> printf("---------------------------------------------- DONE!!\n");
> }
>
> Essentially the added code, creates an endpoint using vka and calls
> seL4_Wait() on it... I expect the code to block forever since there are no
> other threads that can unblock it...
>
> - Build it and run it with:
>
> make pc99_hello-2_defconfig
> make
> make simulate
>
>
> Expected output:
>
> Booting all finished, dropped to user space
> 4 untypeds of size 12
> 4 untypeds of size 13
> [...]
> 6 untypeds of size 29
> WAITING----------------------------------------------
>
>
> - Now change the configuration using 'make menuconfig' and select:
>
> seL4 Kernel -> Build Options -> Compiler optimisation flag (-O2)
>
> and change it to -O0, save the new configuration.
>
> - Rebuild and run:
>
> make simulate
>
>
> Now you get a kernel exception:
>
> [...]
> 6 untypeds of size 29
> WAITING----------------------------------------------
>
> ========== KERNEL EXCEPTION ==========
> Vector: 0xd
> ErrCode: 0xa658
> IP: 0xe0118ce5
> SP: 0xffaf7e28
> FLAGS: 0x86
> CR0: 0x8001003b
> CR2: 0x0 (page-fault address)
> CR3: 0x142000 (page-directory physical address)
> CR4: 0x100290
>
> Stack Dump:
> *0xffaf7e28 == 0xe011a658
> *0xffaf7e2c == 0x0
> *0xffaf7e30 == 0x0
> *0xffaf7e34 == 0xe011a658
> *0xffaf7e38 == 0x8
> *0xffaf7e3c == 0x202
> *0xffaf7e40 == 0x0
> *0xffaf7e44 == 0x0
> *0xffaf7e48 == 0x10
> *0xffaf7e4c == 0x7
> *0xffaf7e50 == 0x0
> *0xffaf7e54 == 0x0
> *0xffaf7e58 == 0x0
> *0xffaf7e5c == 0x0
> *0xffaf7e60 == 0x0
> *0xffaf7e64 == 0x0
> *0xffaf7e68 == 0x0
> *0xffaf7e6c == 0x0
> *0xffaf7e70 == 0x0
> *0xffaf7e74 == 0x0
>
> Halting...
> halting...
> Kernel entry via Interrupt, irq 157
>
>
> Version info:
>
> - gcc: gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11)
> - qemu: QEMU emulator version 2.0.0, Copyright (c) 2003-2008 Fabrice
> Bellard
> - Build environment: CentOS Linux release 7.3.1611 (Core)
>
>
> Other info:
>
> - gcc 4.8.5 doesn't seem to support the 'Nehalem' x86 microarchitecture,
> so I am selecting the 'Generic' microarchitecture (Toolchain Options ->
> X86
> microarchitecture)
> - Even the tutorial 'hello-timer' fails exactly with the same exception
> without any modifications if you build the kernel with -O0.
> - Tested on a Beaglebone black: no problems compiling kernel with -O0
>
>
> Regards,
> Fabrizio Bertocci
> Real-Time Innovations, Inc.
>
>
>
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