On 11/14/2012 12:38 AM, Vivek Goyal wrote:
> A 32bit arch can prepare ELF64 headers. For example for PAE case to
> preresent file offsets 64bit but data size at the offset still remains
> 32bit. If we just base our decision based on EI_CLASS, then we will try
> to read 64bit data from file and can run into various issues.
>
> We ran into following issue when we tried to run vmcore-dmesg on a 32bit
> PAE system vmcore which had 64bit elf headers.
>
> No program header covering vaddr 0xc0a6a688c0b89100found kexec bug?
>
> Basically we try to read value of log_buf variable from address
> log_buf_vaddr. We read in 64bit value and then pass that value again
> to vaddr_to_offset() in an attempt to get to actual log_buf start
> and get error message.
>
> So determine the machine pointer size based on ELF class and arch and read
> the bytes from file accordingly.
>
> v2: Fixed the code as per suggestion from Eric.
>
> Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
Ack
> ---
> vmcore-dmesg/vmcore-dmesg.c | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> Index: kexec-tools/vmcore-dmesg/vmcore-dmesg.c
> ===================================================================
> --- kexec-tools.orig/vmcore-dmesg/vmcore-dmesg.c 2012-08-01 13:27:09.304878654 -0400
> +++ kexec-tools/vmcore-dmesg/vmcore-dmesg.c 2012-11-13 11:32:33.184358230 -0500
> @@ -89,6 +89,24 @@ static uint64_t vaddr_to_offset(uint64_t
> exit(30);
> }
>
> +static unsigned machine_pointer_bits(void)
> +{
> + uint8_t bits = 0;
> +
> + /* Default to the size of the elf class */
> + switch(ehdr.e_ident[EI_CLASS]) {
> + case ELFCLASS32: bits = 32; break;
> + case ELFCLASS64: bits = 64; break;
> + }
> +
> + /* Report the architectures pointer size */
> + switch(ehdr.e_machine) {
> + case EM_386: bits = 32; break;
> + }
> +
> + return bits;
> +}
> +
> static void read_elf32(int fd)
> {
> Elf32_Ehdr ehdr32;
> @@ -389,7 +407,8 @@ static uint64_t read_file_pointer(int fd
> {
> uint64_t result;
> ssize_t ret;
> - if (ehdr.e_ident[EI_CLASS] == ELFCLASS64) {
> +
> + if (machine_pointer_bits() == 64) {
> uint64_t scratch;
> ret = pread(fd, &scratch, sizeof(scratch), addr);
> if (ret != sizeof(scratch)) {
>
> _______________________________________________
> kexec mailing list
> kexec at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
--
Thanks
Dave
