Initramfs specified by INITRD= not found by Linux

[synackd]

When testing with the QEMU board, Linux seems to be unable to find the initramfs passed via INITRD=in the make command, only seeming to work when the initramfs is compiled into the kernel via CONFIG_INITRAMFS_SOURCE.

For instance, when building the QEMU board with Linux 4.14.62 and the following make command:

make BOARD=qemu KERNEL=bzImage INITRD=initramfs.cpio.xz

...the following is the trimmed output of Linux:

[...]
[    1.126287] VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
[    1.131970] Please append a correct "root=" boot option; here are the available partitions:
[    1.137506] 0100           65536 ram0 
[    1.137542]  (driver?)
[    1.148742] 0101           65536 ram1 
[    1.148757]  (driver?)
[    1.157381] 0102           65536 ram2 
[    1.157392]  (driver?)
[    1.166110] 0103           65536 ram3 
[    1.166121]  (driver?)
[    1.174361] 0104           65536 ram4 
[    1.174371]  (driver?)
[    1.183369] 0105           65536 ram5 
[    1.183379]  (driver?)
[    1.191239] 0106           65536 ram6 
[    1.191248]  (driver?)
[    1.199519] 0107           65536 ram7 
[    1.199532]  (driver?)
[    1.206887] 0108           65536 ram8 
[    1.206897]  (driver?)
[    1.215189] 0109           65536 ram9 
[    1.215201]  (driver?)
[    1.222033] 010a           65536 ram10 
[    1.222042]  (driver?)
[    1.230619] 010b           65536 ram11 
[    1.230639]  (driver?)
[    1.238051] 010c           65536 ram12 
[    1.238061]  (driver?)
[    1.246527] 010d           65536 ram13 
[    1.246538]  (driver?)
[    1.252880] 010e           65536 ram14 
[    1.252890]  (driver?)
[    1.259175] 010f           65536 ram15 
[    1.259203]  (driver?)
[    1.266338] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[    1.269803] Kernel Offset: disabled
[    1.273164] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

The kernel cannot find the initramfs.cpio.xz, even though it is included in the linuxboot.rom.

EDIT: Clarified that INITRD= is a build parameter, not a kernel parameter.

[synackd]

I suspected it might have something to do with telling the kernel where the initramfs is loaded here in dxe/linuxboot.c:

               uintptr_t hdr = (uintptr_t) loaded_image->ImageBase;
               *(uint32_t*)(hdr + 0x218) = (uint32_t)(uintptr_t) initrd_buffer;
               *(uint32_t*)(hdr + 0x21c) = (uint32_t)(uintptr_t) initrd_length;

I tried replacing this block with struct names as specified in https://www.kernel.org/doc/Documentation/x86/boot.txt:

               struct boot_params * base = (struct boot_params*) loaded_image->ImageBase;
               base->hdr.ramdisk_image = (uint32_t)(uintptr_t) initrd_buffer;
               base->hdr.ramdisk_size  = (uint32_t)(uintptr_t) initrd_length;

but that had no effect.

[tlaurion]

@rminnich?

[rminnich]

if you need to point to where the kernel is in memory, use the initrdmem option. No need to hack code.

[synackd]

What about kernels before 5.8 (I'm using 4.14.62)? The Linuxboot DXE is already loading the initramfs and pointing the kernel header to it (the code block I referenced) like a bootloader (e.g. GRUB) would. I assume this worked before?

Perhaps the other obligatory fields mentioned in Documentation/x86/boot.txt need to be set as well.

[synackd]

@rminnich Sorry, I realize that my initial comment was ambiguous and I have reworded it. I'm specifying INITRD= as an argument to make, not as a kernel parameter.

[synackd]

Looks like the kernel still needs the EFI_BDS patch so that boot_params->hdr.ramdisk_image doesn't get overwritten to NULL.

For 4.14.62:

diff -u --recursive ../../clean/linux-4.14.62/arch/x86/boot/compressed/eboot.c linux-4.14.62/arch/x86/boot/compressed/eboot.c
--- ../../clean/linux-4.14.62/arch/x86/boot/compressed/eboot.c  2018-08-09 06:16:40.000000000 -0400
+++ linux-4.14.62/arch/x86/boot/compressed/eboot.c      2018-08-09 10:13:11.801000000 -0400
@@ -630,8 +630,8 @@
        u16 *s2;
        u8 *s1;
        int i;
-       unsigned long ramdisk_addr;
-       unsigned long ramdisk_size;
+       unsigned long ramdisk_addr = 0;
+       unsigned long ramdisk_size = 0;
 
        efi_early = c;
        sys_table = (efi_system_table_t *)(unsigned long)efi_early->table;
@@ -686,9 +686,6 @@
        /* Fill in upper bits of command line address, NOP on 32 bit  */
        boot_params->ext_cmd_line_ptr = (u64)(unsigned long)cmdline_ptr >> 32;
 
-       hdr->ramdisk_image = 0;
-       hdr->ramdisk_size = 0;
-
        /* Clear APM BIOS info */        memset(bi, 0, sizeof(*bi));
 
@@ -712,10 +709,16 @@
 
        if (status != EFI_SUCCESS)
                goto fail2;
-       hdr->ramdisk_image = ramdisk_addr & 0xffffffff;
-       hdr->ramdisk_size  = ramdisk_size & 0xffffffff;-       boot_params->ext_ramdisk_image = (u64)ramdisk_addr >> 32;
-       boot_params->ext_ramdisk_size  = (u64)ramdisk_size >> 32;
++       // don't overwrite the bzImage or loader provided ramdisk pointer
+       // unless the kernel command line specified a different one.+       if (ramdisk_addr != 0)
+       {
+               hdr->ramdisk_image = ramdisk_addr & 0xffffffff;
+               hdr->ramdisk_size  = ramdisk_size & 0xffffffff;
+               boot_params->ext_ramdisk_image = (u64)ramdisk_addr >> 32;
+               boot_params->ext_ramdisk_size  = (u64)ramdisk_size >> 32;
+       }
 
        return boot_params;
 fail2

For a more contemporary kernel like 5.16-rc3:

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index f14c4ff..d1127dc 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -411,9 +411,6 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
        efi_set_u64_split((unsigned long)cmdline_ptr,
                          &hdr->cmd_line_ptr, &boot_params->ext_cmd_line_ptr);
 
-       hdr->ramdisk_image = 0;
-       hdr->ramdisk_size = 0;
-
        efi_stub_entry(handle, sys_table_arg, boot_params);
        /* not reached */

[synackd]

Perhaps Linuxboot could support the newer EFI stub v1.0 which finds and load the initrd which is exposed via the LoadFile2 protocol?