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

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

----- 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 >