Re: Compressed kernels currently won't boot

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2019-07-31 at 22:19 +0200, Helge Deller wrote:
> On 31.07.19 21:56, James Bottomley wrote:
> > On Wed, 2019-07-31 at 21:46 +0200, Helge Deller wrote:
> > > On 31.07.19 21:44, Sven Schnelle wrote:
> > > > Hi James,
> > > > 
> > > > On Wed, Jul 31, 2019 at 12:40:12PM -0700, James Bottomley
> > > > wrote:
> > > > 
> > > > > What about causing the compressed make to build both a
> > > > > stripped and a non-stripped bzImage (say sbzImage and
> > > > > bzImage).  That way you always have the stripped one
> > > > > available for small size things like boot from tape or
> > > > > DVD?  but in the usual case we use the bzImage with full
> > > > > contents.
> > > > 
> > > > In that case we would also need to build two lifimages - how
> > > > about adding a config option option? Something like "Strip
> > > > debug information from compressed kernel images"?
> > > 
> > > I agree, two lifimages don't make sense. Only one vmlinuz gets
> > > installed. Instead of the config option, I tink my latest patch
> > > is better.
> > 
> > It doesn't solve the problem that if a stripped compressed image is
> > >
> > 128kb then it overwrites the decompress area starting at 0x00100000
> > so we can't decompress the end because we've already overwritten it
> > before the decompressor gets to it.
> 
> I don't get this point.
>   hppa64-linux-gnu-objdump -h vmlinuz
> shows:
> Sections:
> Idx Name          Size      VMA               LMA               File
> off  Algn
>    0
> .head.text    00000084  00000000000e0000  00000000000e0000  00001000 
>  2**2
>                    CONTENTS, ALLOC, LOAD, READONLY, CODE
>    1
> .opd          00000340  00000000000e0090  00000000000e0090  00001090 
>  2**3
>                    CONTENTS, ALLOC, LOAD, DATA
>    2
> .dlt          00000160  00000000000e03d0  00000000000e03d0  000013d0 
>  2**3
>                    CONTENTS, ALLOC, LOAD, DATA
>    3 .rodata.compressed
> 01f3c2b0  00000000000e0530  00000000000e0530  00001530  2**0
>                    CONTENTS, ALLOC, LOAD, DATA
>    4
> .text         00005cc0  000000000201d000  000000000201d000  01f3e000 
>  2**7
>                    CONTENTS, ALLOC, LOAD, READONLY, CODE
>    5
> .data         00000060  0000000002022cc0  0000000002022cc0  01f43cc0 
>  2**3
>                    CONTENTS, ALLOC, LOAD, DATA
> 
> Only .head.text gets loaded at e0000, and it is basically just a few
> bytes which sets-up registers and jump to .text segment (at 0201d000
> in this case).

Actually, you're looking at the wrong thing, you want to look at the
program header (the segments) not the section header.  It's the program
header we load.  If I extract this from the current debian kernel we
get 

jejb@ion:~/git/linux-build/arch/parisc/boot/compressed> readelf -l /boot/vmlinuz-4.19.0-5-parisc64-smp 

Elf file type is EXEC (Executable file)
Entry point 0xe0000
There are 4 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0x0000000000001040 0x0000000000000000
                 0x00000000000000e0 0x00000000000000e0  R E    0x8
  LOAD           0x0000000000001000 0x00000000000e0000 0x00000000000e0000
                 0x00000000000004d8 0x00000000000004d8  RWE    0x1000
  LOAD           0x0000000000002000 0x0000000001400000 0x0000000001400000
                 0x00000000003dd46c 0x00000000003e1000  RWE    0x1000
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RWE    0x10

 Section to Segment mapping:
  Segment Sections...
   00     
   01     .head.text .opd .dlt 
   02     .text .data .rodata .eh_frame .bss 
   03     

The two LOAD sections corresponding to what PALO actually loads. The
problem happens if the length of the first load section is bigger than
0x20000. Now if you look what happens after your change:

jejb@ion:~/git/linux-build/build/parisc64/arch/parisc/boot> readelf -l bzImage 

Elf file type is EXEC (Executable file)
Entry point 0xe0000
There are 4 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0x0000000000001040 0x0000000000000000
                 0x00000000000000e0 0x00000000000000e0  R E    0x8
  LOAD           0x0000000000001000 0x00000000000e0000 0x00000000000e0000
                 0x00000000004ae760 0x00000000004ae760  RWE    0x1000
  LOAD           0x00000000004b0000 0x000000000118a000 0x000000000118a000
                 0x0000000000006044 0x000000000000a000  RWE    0x1000
  GNU_STACK  0    0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RWE    0x10

 Section to Segment mapping:
  Segment Sections...
   00     
   01     .head.text .opd .dlt .rodata.compressed 
   02     .text .data .rodata .eh_frame .bss 
   03     

So the first section tries to load between 0x000e0000-0x0058e760 and
that's overwritten at 0x00100000 when the decompression starts because
0x00100000 is our KERNEL_BINARY_TEXT_START.  The result for me is that
I get the Decompressing linux ... message followed by a HPMC.

James