Re: [kvm-unit-tests PATCH 1/3] riscv: Add Image header to flat binaries

[Andrew Jones <andrew.jones@linux.dev>]

On Wed, Dec 18, 2024 at 05:06:09PM -0600, Samuel Holland wrote:
> Hi Drew,
> 
> On 2024-12-18 4:13 AM, Andrew Jones wrote:
> > On Mon, Dec 09, 2024 at 10:44:40PM -0600, Samuel Holland wrote:
> >> This allows flat binaries to be understood by U-Boot's booti command and
> >> its PXE boot flow.
> >>
> >> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> >> ---
> >>  riscv/cstart.S | 16 +++++++++++++++-
> >>  1 file changed, 15 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/riscv/cstart.S b/riscv/cstart.S
> >> index b7ee9b9c..106737a1 100644
> >> --- a/riscv/cstart.S
> >> +++ b/riscv/cstart.S
> >> @@ -39,15 +39,29 @@
> >>   * The hartid of the current core is in a0
> >>   * The address of the devicetree is in a1
> >>   *
> >> - * See Linux kernel doc Documentation/riscv/boot.rst
> >> + * See Linux kernel doc Documentation/arch/riscv/boot.rst and
> >> + * Documentation/arch/riscv/boot-image-header.rst
> >>   */
> >>  .global start
> >>  start:
> >> +	j	1f
> >> +	.balign	8
> >> +	.dword	0				// text offset
> > 
> > When I added a header like this for the bpi I needed the text offset to be
> > 0x200000, like Linux has it.  Did you do something to avoid that?
> 
> It turns out that U-Boot on my board is configured to ignore the first 0x200000
> bytes of DRAM entirely, so the binary ended up at the right address for the
> wrong reason. I can send a v2 with this field changed to 0x200000 (which also
> works on my board).

Sounds good.

Thanks,
drew

> 
> Regards,
> Samuel
> 
> >> +	.dword	stacktop - ImageBase		// image size
> >> +	.dword	0				// flags
> >> +	.word	(0 << 16 | 2 << 0)		// version
> >> +	.word	0				// res1
> >> +	.dword	0				// res2
> >> +	.ascii	"RISCV\0\0\0"			// magic
> >> +	.ascii	"RSC\x05"			// magic2
> >> +	.word	0				// res3
> >> +
> >>  	/*
> >>  	 * Stash the hartid in scratch and shift the dtb address into a0.
> >>  	 * thread_info_init() will later promote scratch to point at thread
> >>  	 * local storage.
> >>  	 */
> >> +1:
> >>  	csrw	CSR_SSCRATCH, a0
> >>  	mv	a0, a1
> >>  
> >> -- 
> >> 2.39.3 (Apple Git-146)
> >>
> > 
> > Thanks,
> > drew
>