PPC: problem with syscalls
Hello everybody,
I've a problem with examples/timer.c. I've tried to launch it on my mpc860t board, if I start the timer and if I
press a key after one or more interrupts occured, the u-boot crashes. The problem is that an interrupt handler
uses a system call (mon_printf) while the main loop is inside a system call (mon_getc). During a system call,
the LR and SRRx are saved at a fixed location (0xcf4, 0xcf8 and 0xcfc) then the return address of the mon_printf
in the main loop is overridden by the return address of the mon_getc in the interrupt handler. To avoid this problem,
I think that we need to use a stack to store the return addresses (and the SRRx) of the system calls.
What's your opinion ?
Best regards
Quoted 15 lines · Pierre AUBERT
Hello everybody,
I've a problem with
examples/timer.c. I've tried to launch it on my mpc860t board, if I start the timer and if I
press a key after one or more interrupts occured, the u-boot crashes. The problem is that an interrupt handler
uses a system call (mon_printf) while the main loop is inside a system call (mon_getc). During a system call,
the LR and SRRx are saved at a fixed location (0xcf4,0xcf8and0xcfc) then the return address of themon_printf
in the main loop is overridden by the return address of themon_getcin the interrupt handler. To avoid this problem,
I think that we need to use a stack to store the return addresses (and the SRRx) of the system calls.
Dear Wolfgang,
Please find attached a patch fixing the problem described above. A little stack (located between the end of the syscall exception handler and the beginning of the following exception) is used to save the LR and SRRx. With this patch, examples/timer is running fine.
Best regards.
CHANGELOG:
* Patch by Pierre Aubert , 28 Nov 2002
Fix nested syscalls bug in standalone applications.
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Quoted 5 lines · In message <[email protected]> you wrote:
Please find attached a patch fixing the problem described above. A little stack (located between the end of the syscall exception handler and the beginning of the following exception) is used to save the LR and SRRx. With this patch, examples/timer is running fine.
Added (although I still/now think we should implement a portable method instead).
Best regards,
Wolfgang Denk
Signature · 4 lines
Software Engineering: Embedded and Realtime Systems, Embedded Linux Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd at denx.de "If you own a machine, you are in turn owned by it, and spend your time serving it..." - Marion Zimmer Bradley, _The Forbidden Tower_
Quoted 14 lines · In message <[email protected]> you wrote:
I've a problem with
examples/timer.c. I've tried to launch it on my mpc860t board, if I start the timer and if I
press a key after one or more interrupts occured, the u-boot crashes. The problem is that an interrupt handler
uses a system call (mon_printf) while the main loop is inside a system call (mon_getc). During a system call,
the LR and SRRx are saved at a fixed location (0xcf4,0xcf8and0xcfc) then the return address of themon_printf
in the main loop is overridden by the return address of themon_getcin the interrupt handler. To avoid this problem,
I think that we need to use a stack to store the return addresses (and the SRRx) of the system calls.
Quoted 1 line
What's your opinion ?
We should probably follow Robert Kaiser's advise and use plainold pointer tables as we did before. When I switched to use syscalls it seemed like a good idea, but I was not thinking about other archi- tectures then.
[Sorry it took me so long to repply.]
Best regards,
Wolfgang Denk
Signature · 5 lines
Software Engineering: Embedded and Realtime Systems, Embedded Linux
Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd at denx.de
In an infinite universe all things are possible, including the possi-
bility that the universe does not exist.
- Terry Pratchett, _The Dark Side of the Sun_