Vivek Goyal <vgoyal at redhat.com> writes:
> 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 data size based on arch and read the bytes from
> file accordingly.
The basic code change is sound. However the naming is problematic.
Let me suggest:
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;
}
> Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
> ---
> vmcore-dmesg/vmcore-dmesg.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> Index: kexec-tools/vmcore-dmesg/vmcore-dmesg.c
> ===================================================================
> --- kexec-tools.orig/vmcore-dmesg/vmcore-dmesg.c 2012-08-03 15:46:54.000000000 -0400
> +++ kexec-tools/vmcore-dmesg/vmcore-dmesg.c 2012-11-08 05:30:17.918099858 -0500
> @@ -89,6 +89,23 @@ static uint64_t vaddr_to_offset(uint64_t
> exit(30);
> }
>
> +/*
> + * For PAE arch, one can prepare 64bit ELF headers to make offsets 64bit in
> + * file but data size still remains 32bit. Determine data size based on arch
> + * (e_machine).
> + *
> + * returns 1 if arch passed in is 64bit
> + */
> +static bool file_data_size_64bit(unsigned int e_machine)
> +{
> + switch(e_machine) {
> + /* TODO: keep on adding 32bit arch to get vmcore-dmesg right */
> + case EM_386:
> + return 0;
> + }
> + return 1;
> +}
> +
> static void read_elf32(int fd)
> {
> Elf32_Ehdr ehdr32;
> @@ -389,7 +406,8 @@ static uint64_t read_file_pointer(int fd
> {
> uint64_t result;
> ssize_t ret;
> - if (ehdr.e_ident[EI_CLASS] == ELFCLASS64) {
> + if (ehdr.e_ident[EI_CLASS] == ELFCLASS64 &&
> + file_data_size_64bit(ehdr.e_machine)) {
Then this test can become:
if (machine_pointer_bits() == 64) {
> uint64_t scratch;
> ret = pread(fd, &scratch, sizeof(scratch), addr);
> if (ret != sizeof(scratch)) {
