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Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB
From: |
Robbie Harwood |
Subject: |
Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB |
Date: |
Tue, 16 Nov 2021 10:17:20 -0500 |
Daniel Axtens <dja@axtens.net> writes:
> RHEL9.0 builds were failing to boot with bizzare errors about module
> licensing.
>
> This was first reported under PFW but reproduces under SLOF.
>
> What is going wrong?
> --------------------
>
> Much debugging later, it turned out that this was because their image was
> greater than 2MB - 16KB in size:
>
> - The core.elf was 2126152 = 0x207148 bytes in size with the following
> program headers (per readelf):
>
> Entry point 0x200000
> There are 4 program headers, starting at offset 52
>
> Program Headers:
> Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
> LOAD 0x000160 0x00200000 0x00200000 0x21f98 0x2971c RWE 0x8
> GNU_STACK 0x0220f8 0x00000000 0x00000000 0x00000 0x00000 RWE 0x4
> LOAD 0x0220f8 0x00232000 0x00232000 0x1e4e50 0x1e4e50 RWE 0x4
> NOTE 0x206f48 0x00000000 0x00000000 0x00200 0x00000 R 0x4
>
> - SLOF places the ELF file at 0x4000 (after the reserved space for
> interrupt handlers etc.) upwards. The image was 2126152 = 0x207148
> bytes in size, so it runs from 0x4000 - 0x20b148. We'll call 0x4000 the
> load address.
>
> 0x0 0x4000 0x20b148
> |----------|--------------|
> | reserved | ELF contents |
>
> - SLOF then copies the first LOAD program header (for .text). That runs
> for 0x21f98 bytes. It runs from
> (load addr + 0x160) to (load addr + 0x160 + 0x21f98)
> = 0x4160 to 0x260f8
> and we copy it to 0x200000 to 0x221f98. This overwrites the end of the
> image:
>
> 0x0 0x4000 0x200000 0x221f98
> |----------|------------|---------------|
> | reserved | ELF cont.. | .text section |
>
> - SLOF zeros the bss up to PhysAddr + MemSize = 0x22971c
>
> 0x0 0x4000 0x200000 0x221f98 0x22971c
> |----------|------------|---------------|--------|
> | reserved | ELF cont.. | .text section | bss 0s |
>
> - SLOF then goes to fulfil the next LOAD header (for mods), which is
> for 0x1e4e50 bytes. We copy from
> (load addr + 0x220f8) to (load addr + 0x220f8 + 0x1e4e50)
> = 0x260f8 to 0x20af48
> and we copy it to 0x232000 to 0x416e50:
>
> 0x0 0x4000 0x200000 0x221f98 0x22971c
> |----------|------------|---------------|--------|
> | reserved | ELF cont.. | .text section | bss 0s |
> |-------------|
> | copied area |
> 0x260f8 0x20af48
>
> This goes poorly:
>
> 0x0 0x4000 0x200000 0x221f98 0x22971c 0x232000 0x40bf08
> 0x416e50
>
> |----------|------------|---------------|--------|-----|-----------|-------------|
> | reserved | ELF cont.. | .text section | bss 0s | pad | some mods | .text
> start |
>
> This matches the observations on the running system - 0x40bf08 was where
> the contents of memory no longer matched the contents of the ELF file.
>
> This was reported as a license verification failure on SLOF as the
> last module's .module_license section fell past where the corruption
> began.
>
> load-base
> ---------
>
> From LoPAR:
>
> B.10.1 Load Address
>
> The client’s load address is specified by the value of the load-base
> Configuration Variable. The value of load-base defines the default
> load address for client programs when using the load
> method. Load-base shall be a real address in real mode or a virtual
> address in virtual mode. Note that this address represents the area,
> within the first LMB, into which the client program file will be
> read by load; it does not correspond to the addresses at which the
> program will be executed. All of physical memory from load-base to
> either the start of OF physical memory or the end of physical
> memory, whichever comes first, shall be available for loading the
> client program.
>
> Note: The load-base address represents the area into which the
> client program will be read by load and does not correspond
> to the address at which the program will be executed.
>
> We can specify load-base via setting a configuration variable, via
> CAS, or via an 1275 PowerPC Note.
>
> We can indeed override load-base and successfully load such a binary
> in SLOF. Drop to the OF shell and run:
>
> 0 > a000000 to load-base-override
> 0 > boot
>
> Sadly, asking people to drop to OF is not a super practical
> solution. SLOF ignores the 1275 PowerPC Note, which is the only thing
> we can (sanely) set in grub rather than in OF.
>
> PFW's load-base also defaults to 0x4000 but will honour the note. (The
> PFW team has been asking me to get grub to include the note and set
> appropriate values. See the next patch.)
>
> Fixing this
> -----------
>
> Unless I'm mistaken, if we want backwards compat with SLOF, we will
> need to change grub so that we ask the linker instruct the loader to
> load the program data somewhere else, giving us more headroom for the
> ELF image.
>
> This is fairly straight-forward to do. I've picked 8MB as that's a
> fairly common size for the PReP partition. We could potentially pick
> 4MB, I think I've seen some partitions that size too.
>
> The tests with powerpc32 using the OpenBIOS OF implementation seem to
> still work. I have no 32-bit Apple hardware to test on.
>
> Signed-off-by: Daniel Axtens <dja@axtens.net>
Shipping this one already.
Reviewed-by: Robbie Harwood <rharwood@redhat.com>
Be well,
--Robbie
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- [PATCH 0/2] powerpc-ieee1275: support larger core.elf images, Daniel Axtens, 2021/11/15
- [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB, Daniel Axtens, 2021/11/15
- Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB,
Robbie Harwood <=
- Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB, Vladimir 'phcoder' Serbinenko, 2021/11/16
- Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB, Robbie Harwood, 2021/11/16
- Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB, John Paul Adrian Glaubitz, 2021/11/16
- Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB, John Paul Adrian Glaubitz, 2021/11/16
- Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB, Robbie Harwood, 2021/11/16
- Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB, Vladimir 'phcoder' Serbinenko, 2021/11/16
- Re: [PATCH 1/2] powerpc-ieee1275: load grub at 8MB, not 2MB, John Paul Adrian Glaubitz, 2021/11/22
[PATCH 2/2] ieee1275: set real-base in the PowerPC IEEE1275 Note to 32MB, Daniel Axtens, 2021/11/15
Re: [PATCH 0/2] powerpc-ieee1275: support larger core.elf images, John Paul Adrian Glaubitz, 2021/11/23