Re: [Crash-utility] question about phys_base

From: Dave Anderson <anderson(a)redhat.com&gt; Subject: Re: [Crash-utility] question about phys_base Date: Tue, 28 Feb 2012 09:44:09 -0500 (EST) > > > ----- Original Message ----- >> At 02/28/2012 04:52 PM, HATAYAMA Daisuke Wrote: > >>>>> In general, such characteristic should not be used. You should prepare >>>>> a solid interface. Even if using them, it should be limited to as >>>>> workaround to avoid some issue. >>>>> >>>>> Why not use qemu's CPU state? Include it as note information with good >>>>> name, and we can use it to distinguish which. Like: >>>>> >>>>> $ readelf -n vmcore >>>>> >>>>> Notes at offset 0x000001c8 with length 0x00000838: >>>>> Owner Data size Description >>>>> CORE 0x00000150 NT_PRSTATUS (prstatus structure) >>>>> CORE 0x00000150 NT_PRSTATUS (prstatus structure) >>>>> QEMU 0x00000557 Unknown note type: (0x00000000) >>>>> >>>>> Or QEMUCPUState is better? >>>> >>>> Good idea. I will try it, and hope gdb can also work. >>>> >>> >>> Tools basically ignore unknown notes. Looking into gdb, it appears to >>> ignore unknown information. >>> >>> static bfd_boolean >>> elfcore_grok_note (bfd *abfd, Elf_Internal_Note *note) >>> { >>> const struct elf_backend_data *bed = get_elf_backend_data (abfd); >>> >>> switch (note->type) >>> { >>> default: >>> return TRUE; >>> <cut> >>> >>> You might need to add new command to output contents of new note if >>> it's necessary. >> >> My goal is: >> 1. gdb uses NT_PRSTATUS, and can work well >> 2. crash uses unknown notes, and can get phys_base from it. >> >> Another question: >> >> What is QEMUCPUState? I donot find its definition? > > It's just the note's name character string. Either "QEMU", "QEMUCPUState", > or whatever unique character string you prefer would suffice. > >> What note->type shoule be for "QEMU"? If we choose an unused value, the >> value may be used in the future. > > Why not do the same thing as the "VMCOREINFO" note, and leave it > as an "illegal/unknown" type of 0:: > > $ cat /usr/include/elf.h > ... [ cut ] ... > > /* Legal values for note segment descriptor types for core files. */ > > #define NT_PRSTATUS 1 /* Contains copy of prstatus struct */ > #define NT_FPREGSET 2 /* Contains copy of fpregset struct */ > #define NT_PRPSINFO 3 /* Contains copy of prpsinfo struct */ > ... > $ > > $ readelf -a vmcore > ... [ cut ] ... > > Notes at offset 0x00000190 with length 0x00000f1c: > Owner Data size Description > CORE 0x00000150 NT_PRSTATUS (prstatus structure) > CORE 0x00000150 NT_PRSTATUS (prstatus structure) > CORE 0x00000150 NT_PRSTATUS (prstatus structure) > CORE 0x00000150 NT_PRSTATUS (prstatus structure) > CORE 0x00000150 NT_PRSTATUS (prstatus structure) > CORE 0x00000150 NT_PRSTATUS (prstatus structure) > CORE 0x00000150 NT_PRSTATUS (prstatus structure) > CORE 0x00000150 NT_PRSTATUS (prstatus structure) > VMCOREINFO 0x000003e4 Unknown note type: (0x00000000) > $ > It looks OK to me for now. But rigorously, it might be better to give it a name QEMU and then prepare variety of information such as NT_CPUSTATE and others to be needed later.

Thanks. HATAYAMA, Daisuke