Messages in this thread | | | Subject | Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) | From | Dmitry Safonov <> | Date | Tue, 7 Jun 2016 14:38:15 +0300 |
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On 06/07/2016 12:19 AM, Oleg Nesterov wrote: > On 06/01, Dmitry Safonov wrote: >> >> Note, that this will work only if application has changed it's CS. > > So, suppose it changes it's CS and crashes, > >> If the application does 32-bit syscall with __USER_CS, ptrace >> @@ -1355,7 +1355,7 @@ void update_regset_xstate_info(unsigned int size, u64 xstate_mask) >> const struct user_regset_view *task_user_regset_view(struct task_struct *task) >> { >> #ifdef CONFIG_IA32_EMULATION >> - if (test_tsk_thread_flag(task, TIF_IA32)) >> + if (!user_64bit_mode(task_pt_regs(task))) >> #endif > > then coredump will do fill_elf_header(view->e_machine) and use EM_X86_64 > instead of EM_386, or vice versa... > > I simply can't understand is this better or worse, I guess gdb or any > other tool which looks at this coredump will be confused anyway.
Oleg, thanks for your reply!
At least, gdb will have all registers at that moment. Firstly, I did it for returning with GET_REGSET corresponding register set. So ptrace-attaching to a task with 64-bit code selector would return 64-bit register set and contrariwise. (as task may use all 64-bit registers, that seems logical for me even if it has been loaded as 32-bit ELF)
And for coredump -- I guess it will show full register set on the crash moment and show proper disasm around that place. And for my purpose -- that's really what I need, to generate 32-bit ELF core file on crash after changing CS.
I did it for C/R of 32-bit application with changing code selector from 64-bit. So last thing restorer does - unmap itself (it's pie blob) and sigreturn to application. So if the application crashes after it - it will be good to have 32-bit coredump as for the original application.
Thanks, Dmitry Safonov
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