Messages in this thread | | | From | Roland McGrath <> | Subject | Re: parsic/sh/sparc tracehook breakage when tracing signals | Date | Thu, 11 Feb 2010 19:07:25 -0800 (PST) |
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> when i ported the Blackfin code to the tracehook framework, i copied a latent > bug from the sparc port. trying to trace another process while handling > signals no longer worked (and subsequently broke some of the gdb tests).
What you mean is that single-step into a signal handler fails to stop at the first instruction of the handler. (Instead it stops after the first instruction in the handler's prologue.)
> this was due to calling tracehook_signal_handler() with the last argument > (stepping) always as 0. if we look at the definition of this function in > linux/tracehook.h, we see that calling the function stepping=0 is pointless: > if (stepping) > ptrace_notify(SIGTRAP);
Indeed, it doesn't do anything else right now. But the reason to call it regardless is so that every arch is consistent in telling the generic code what is going on. If we add a future feature to ptrace (or something else) to track signal handler setups, that feature may very well not be one that fires only when single-step is in use. An arch that is set up now to call tracehook_signal_handler() exactly as that function's kerneldoc says to do will be prepared for such things to work without later arch changes.
> after Roland pointed out some more stuff, i went back and looked at all the > tracehook arches in the tree. it seems like these arches are all broken in > the same way: > parisc (arch/parisc/kernel/signal.c) > SuperH (64bit only) (arch/sh/kernel/signal_64.c) > Sparc (all bits) (arch/sparc/kernel/signal{_32,32,_64}.c) > > seems like you guys should just change the last argument to: > test_thread_flag(TIF_SINGLESTEP)
Whether there is a TIF_SINGLESTEP and what it means is arch-specific. If arch_has_single_step(), then the argument should be nonzero if user_enable_single_step() is in force at the time of handler setup.
In parisc, it should test for either TIF_SINGLESTEP or TIF_BLOCKSTEP.
In sh, going from what signal_32.c does, it should indeed do as you say.
In sparc, arch_has_single_step()==0, so there is nothing to do.
Thanks, Roland
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