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):
        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 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

- 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

========== 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

Kernel entry via Interrupt, irq 157

Version info:

Other info:

Fabrizio Bertocci
Real-Time Innovations, Inc.