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).
See: arch/parisc/boot/compressed/head.S
How should that get bigger than 128KB ?
Then the code in .text decompresses the whole kernel image behind itself
(behind "data").
Then the ELF loader moves the parts from the high-memory to the final
destination (e.g. 1000000).
The steps are:
1. palo loads vmlinuz into memory.
2. vmlinuz' head starts, and decompress_kernel() in arch/parisc/boot/compressed/misc.c
decompresses the vmlinuz file to a vmlinux file and stores it to
vmlinux_addr (which is behind the bss section of the boot decompressor).
3. Then the original kernel entry is started (arch/parisc/kernel/entry.S)
which moves the code to where it belongs and starts the kernel.
Helge
What we could possibly do is be clever and align the .rodata.compressed
so its last text byte ends where the uncompressed kernel text would
end. We could be even more clever and split .rodata.compressed into a
load and a noload part so we would only load the part of the compressed
kernel we need. Then the lifimage creation scripts could discard the
noload part containing the debug symbols.
James
