Hi Chen, On Thu, 12 Nov 2020 12:34:36 +0800 Chen Yu <yu.chen.s...@gmail.com> wrote:
> Hi Masami, > > On Wed, Nov 11, 2020 at 5:37 PM Masami Hiramatsu <mhira...@kernel.org> wrote: > > > > Hi Chen, > > > > On Tue, 10 Nov 2020 23:39:53 +0800 > > Chen Yu <yu.chen.s...@gmail.com> wrote: > > > > > Hi Masami, > > > Thanks for writing bootconfig and it is useful for boot up trace event > > > debugging. > > > > Thanks for testing! > > > > > However it was found that on 5.10-rc2 the bootconfig does not work and it > > > shows > > > "'bootconfig' found on command line, but no bootconfig found" > > > And the reason for this is the kernel found the magic number to be > > > incorrect. > > > I've added some hack in kernel to dump the first 12 bytes, it shows: > > > "OTCONFIG". So printed more content ahead we can find > > > "#BOOTCONFIG" ahead. So it looks that there is some alignment during > > > initrd load, and get_boot_config_from_initrd() might also deal with it. > > > That is > > > to say: > > > data = (char *)initrd_end - BOOTCONFIG_MAGIC_LEN; > > > might do some alignment? > > > > Hrm, interesting. So initrd_end might be aligned. Could you print out the > > actuall address of initrd_end? > I've done some investigation, it looks like this issue is not related > to alignment, but related to > the bootloader that has provided an inaccurate ramdisk size via > boot_params.hdr.ramdisk_size. Yeah, it seems to happen. bootloader can pass wrong (bigger) size to kernel. BTW, what bootloader would you use? > The actual size of initrd is: > ls /boot/initrd.img-5.10.0-rc3-e1000e-hw+ -l > -rw-r--r-- 1 root root 48689230 11月 12 00:08 > /boot/initrd.img-5.10.0-rc3-e1000e-hw+ > while the ramdisk size provided by bootloader via > boot_params.hdr.ramdisk_size is > 48689232, which is 2 bytes bigger than the actual size, and this is > why the initrd_end > is bigger than expected and causing the missmatch of magic number. OK. It seems that the bootloader might cut it up to 16 bytes aligned. (But I think that's wrong behavior, there is no reason to do it) > Since there is no guarantee that bootloader provides the accurate > ramdisk size, an compromised > proposal might be that to search for the magic number a little ahead. If the bootloader does such wrong behavior, there is no guarantee that the size is "a little" bigger. IOW, it can be aligned to the page size (4KB-) > For example, the > following patch works for me: > diff --git a/init/main.c b/init/main.c > index 130376ec10ba..60fb125d44f4 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -273,7 +273,10 @@ static void * __init > get_boot_config_from_initrd(u32 *_size, u32 *_csum) > if (!initrd_end) > return NULL; > > - data = (char *)initrd_end - BOOTCONFIG_MAGIC_LEN; > + data = memchr((char *)initrd_end - 2 * BOOTCONFIG_MAGIC_LEN, > + '#', BOOTCONFIG_MAGIC_LEN); > + if (!data) > + return NULL; So this also does not guarantee that we can find "#" in BOOTCONFIG_MAGIC_LEN. We need to find actual code in the bootloader, what it does. > if (memcmp(data, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN)) > return NULL; > > > > And could you tell me which platform are you tested? > > > It is HP ZHAN 99 Mobile Workstation G1 with i5-8300H, Ubuntu 20.04. Hmm, this means x86 Grub2 does this change. Let me check it. Thank you, -- Masami Hiramatsu <mhira...@kernel.org>
