Re: [Crash-utility] [PATCH] filesys: Skip 'vmlinux.o' while searching for vmlinux in 'find_booted_kernel()'

Hi Dave, On Wed, Feb 28, 2018 at 9:09 PM, Dave Anderson <anderson(a)redhat.com&gt; wrote: > > Hi Bhupesh, > > Try this patch: > > $ diff --git a/filesys.c b/filesys.c > index 1b44ad5..74728f1 > --- a/filesys.c > +++ b/filesys.c > @@ -625,7 +625,7 @@ find_booted_kernel(void) > > if (mount_point(kernel) || > !file_readable(kernel) || > - !is_elf_file(kernel)) > + !is_kernel(kernel)) > continue; > > if (CRASHDEBUG(1)) > diff --git a/symbols.c b/symbols.c > index 4db9af7..7910f53 > --- a/symbols.c > +++ b/symbols.c > @@ -3488,7 +3488,8 @@ is_kernel(char *file) > > if (endian_mismatch(file, elf64->e_ident[EI_DATA], 0)) > goto bailout; > - } > + } else > + return FALSE; > > bailout: > return(is_bfd_format(file)); > > Thanks, > Dave I tried this patch and it seems to work fine on my arm64 system. Please feel free to add my Tested-by for the patch. Thanks. > ----- Original Message ----- >> Hi Bhupesh, >> >> Thanks -- mystery solved! >> >> I kind of hate to simply use the file name string as the qualifier, >> though. >> Looking at the ELF headers of the vmlinux.o and vmlinux file, there are >> several notable differences: >> >> $ readelf -a vmlinux >> ELF Header: >> Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 >> Class: ELF64 >> Data: 2's complement, little endian >> Version: 1 (current) >> OS/ABI: UNIX - System V >> ABI Version: 0 >> Type: EXEC (Executable file) >> Machine: AArch64 >> Version: 0x1 >> Entry point address: 0xffff000008080000 >> Start of program headers: 64 (bytes into file) >> Start of section headers: 186677936 (bytes into file) >> Flags: 0x0 >> Size of this header: 64 (bytes) >> Size of program headers: 56 (bytes) >> Number of program headers: 4 >> Size of section headers: 64 (bytes) >> Number of section headers: 42 >> Section header string table index: 41 >> ... >> >> >> $ readelf -a vmlinux.o >> ELF Header: >> Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 >> Class: ELF64 >> Data: 2's complement, little endian >> Version: 1 (current) >> OS/ABI: UNIX - System V >> ABI Version: 0 >> Type: REL (Relocatable file) >> Machine: AArch64 >> Version: 0x1 >> Entry point address: 0x0 >> Start of program headers: 0 (bytes into file) >> Start of section headers: 478638376 (bytes into file) >> Flags: 0x0 >> Size of this header: 64 (bytes) >> Size of program headers: 0 (bytes) >> Number of program headers: 0 >> Size of section headers: 64 (bytes) >> Number of section headers: 34816 >> Section header string table index: 34815 >> ... >> >> There is the "Type", the "Entry point address", and perhaps most notably, >> the vmlinux.o's "Number of program headers:" count of 0, which obviously >> would preclude the file from being usable. >> >> I would prefer to beef up the currently-existing is_kernel() function, >> and use it instead of is_elf_file(). Let me take a look at what works. >> >> Thanks, >> Dave >> >> >> >> ----- Original Message ----- >> > I found this particular issue while compiling and installing >> > a kernel from source on a RHEL arm64 machine. I used the following >> > commands to build and install the kernel from source: >> > >> > # make olddefconfig >> > # make >> > # make modules_install INSTALL_MOD_STRIP=1 && make install >> > >> > This compiles and installs both 'vmlinux' and 'vmlinux.o' at >> > the following standard location - '/lib/modules/<kernel>/build/ >> > >> > Now the problem can be reproduced using the following steps: >> > 1. Update grub to boot the freshly compiled kernel. >> > 2. Reboot machine. >> > 3. Now, run crash on live system, it errors out with the following >> > messages: >> > >> > crash: invalid kernel virtual address: 8470 type: "possible" >> > WARNING: cannot read cpu_possible_map >> > crash: invalid kernel virtual address: 8270 type: "present" >> > WARNING: cannot read cpu_present_map >> > crash: invalid kernel virtual address: 8070 type: "online" >> > WARNING: cannot read cpu_online_map >> > crash: invalid kernel virtual address: 8670 type: "active" >> > WARNING: cannot read cpu_active_map >> > >> > crash: cannot resolve "_stext" >> > >> > 4. Enabling some debug messages in 'find_booted_kernel()' function >> > tells us that it finds 'vmlinux.o' earlier than 'vmlinux' and accepts >> > that as the kernel being boot'ed: >> > >> > find_booted_kernel: check: /lib/modules/4.14.0/build/vmlinux.o >> > find_booted_kernel: found: /lib/modules/4.14.0/build/vmlinux.o >> > >> > 5. Now the problem happens due to following check inside >> > 'find_booted_kernel()' function: >> > >> > if (mount_point(kernel) || >> > !file_readable(kernel) || >> > !is_elf_file(kernel)) >> > continue; >> > >> > 6. Since 'vmlinux.o' is a elf file, is readable and is not >> > mount'able, so the check in point 5 fails and we incorrectly >> > accept this as the kernel being boot'ed, even though >> > there was a 'vmlinux' present inside >> > '/lib/modules/<kernel>/build'. >> > >> > 7. Now, later when crash tries to access symbols (like _stext) >> > using this kernel symbol file, we see errors. >> > >> > Fix this by skipping 'vmlinux.o' from the check in point 5, >> > so that we can select 'vmlinux' correctly as the kernel file. >> > >> > After this fix, crash no longer errors out and we can use >> > full functionality on the crash prompt. >> > >> > Signed-off-by: Bhupesh Sharma <bhsharma(a)redhat.com&gt; >> > --- >> > filesys.c | 14 +++++++++++++- >> > 1 file changed, 13 insertions(+), 1 deletion(-) >> > >> > diff --git a/filesys.c b/filesys.c >> > index 1b44ad5cefa8..9f240d6115a1 100644 >> > --- a/filesys.c >> > +++ b/filesys.c >> > @@ -623,9 +623,21 @@ find_booted_kernel(void) >> > >> > sprintf(kernel, "%s%s", searchdirs[i], dp->d_name); >> > >> > + /* We may run into a special case with >> > + * 'vmlinux.o' been present inside >> > + * '/lib/modules/<kernel>/build/', >> > + * which has some special characteristics - >> > + * this is a elf file, is readable and is not >> > + * mount'able. >> > + * >> > + * So we need to handle this properly here to >> > + * make sure that we get to the real 'vmlinux' >> > + * rather than the 'vmlinux.o' >> > + */ >> > if (mount_point(kernel) || >> > !file_readable(kernel) || >> > - !is_elf_file(kernel)) >> > + !is_elf_file(kernel) || >> > + !(strcmp(dp->d_name, "vmlinux.o"))) >> > continue; >> > >> > if (CRASHDEBUG(1)) >> > -- >> > 2.7.4 >> > >> > >> >> -- >> Crash-utility mailing list >> Crash-utility(a)redhat.com >> https://www.redhat.com/mailman/listinfo/crash-utility >>