On 03/27/2013 04:26 AM, Daniel Walker wrote: > On Mon, Mar 25, 2013 at 10:48:07AM +0100, Denys Vlasenko wrote: >> On 03/19/2013 09:19 PM, Oleg Nesterov wrote: >>>> The above is regarding the situation which I'm running my corepipe_app , >>>> i.e. my system doesn't have a disk to save a core file for parsing. >>> >>> Can't you process the data inplace? You do not need to save it to disk. >> >> Daniel said: >> >>>> I'm trying to get the "dumpers" registers and stack out when it fails. >> >> Registers would be easy'ish to get from coredump: >> they are contained in note sections which are at the beginning >> of the coredump. You can implement necessary parsing without >> too much pain. >> >> Getting at stack would be harder. > > There exists /proc/<pid>/mem and /proc/<pid>/maps on these tasks. If > those don't work then that's a straight up defect.. > >> But by asking kernel to allow you to poke around dead task's >> address space with ptrace() calls you just shift difficulty away from you >> (today you need to implement in-memory ELF parsing) to kernel people >> (they will need to implement *and support* ptracing of coredumping >> tasks). >> >> This is somewhat unfair, considering that coredumping code in kernel >> is already a source of many complications, and that kernel-side coding >> is harder than userspace. >> >> I think you are lucky that ptrace attach even *works* on coredumping task. >> No documentation ever guaranteed such a thing. > > There not much different from userspace between a task running, and one > dumping..
As I see it, dumping task is past the point where it can enter ptrace-stops. It's like asking to ptrace a task which already entered the kernel via exit(0) syscall and complaining that "it doesn't work". Of course it does not: a ptrace-stop can happen only after syscall returns to userspace, and exit() doesn't return. Coredumping is similar: the task is in kernelspace and it won't ever return to userspace. -- vda -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
