Re: [PATCH 1/3] s390x: snippets: Add gitignore as well as linker script and start assembly

[Janosch Frank <frankja@linux.ibm.com>]

On 6/24/21 5:49 PM, Thomas Huth wrote:
> On 24/06/2021 14.01, Janosch Frank wrote:
>> Snippets are small guests That can be run under a unit test as the
>> hypervisor. They can be written in C or assembly. The C code needs a
>> linker script and a start assembly file that jumps to main to work
>> properly. So let's add that as well as a gitignore entry for the new
>> files.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>>   .gitignore                |  1 +
>>   s390x/snippets/c/cstart.S | 15 ++++++++++++
>>   s390x/snippets/c/flat.lds | 51 +++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 67 insertions(+)
>>   create mode 100644 s390x/snippets/c/cstart.S
>>   create mode 100644 s390x/snippets/c/flat.lds
>>
>> diff --git a/.gitignore b/.gitignore
>> index 8534fb7..b3cf2cb 100644
>> --- a/.gitignore
>> +++ b/.gitignore
>> @@ -23,3 +23,4 @@ cscope.*
>>   /api/dirty-log
>>   /api/dirty-log-perf
>>   /s390x/*.bin
>> +/s390x/snippets/*/*.gbin
>> diff --git a/s390x/snippets/c/cstart.S b/s390x/snippets/c/cstart.S
>> new file mode 100644
>> index 0000000..d7f6525
>> --- /dev/null
>> +++ b/s390x/snippets/c/cstart.S
>> @@ -0,0 +1,15 @@
>> +#include <asm/sigp.h>
>> +
>> +.section .init
>> +	.globl start
>> +start:
>> +	/* XOR all registers with themselves to clear them fully. */
>> +	.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
>> +	xgr \i,\i
>> +	.endr
>> +	/* 0x3000 is the stack page for now */
>> +	lghi	%r15, 0x4000 - 160
>> +	brasl	%r14, main
>> +	/* For now let's only use cpu 0 in snippets so this will always work. */
>> +	xgr	%r0, %r0
>> +	sigp    %r2, %r0, SIGP_STOP
>> diff --git a/s390x/snippets/c/flat.lds b/s390x/snippets/c/flat.lds
>> new file mode 100644
>> index 0000000..5e70732
>> --- /dev/null
>> +++ b/s390x/snippets/c/flat.lds
>> @@ -0,0 +1,51 @@
>> +SECTIONS
>> +{
>> +	.lowcore : {
>> +		/*
>> +		 * Initial short psw for disk boot, with 31 bit addressing for
>> +		 * non z/Arch environment compatibility and the instruction
>> +		 * address 0x10000 (cstart64.S .init).
> 
> I think this comment needs some adjustments (0x10000 => 0x4000 and do not 
> talk about cstart64.S)?

Right, will do

> 
> Also, what about switching to 64-bit mode in the snippets?

I thought about that for some time a while ago.
It's not really necessary since the host test can also decide which
guest PSW is used to start the snippet but it also doesn't hurt so I
just added a sam64.

> 
>   Thomas
> 
> 
>> +		 */
>> +		. = 0;
>> +		 LONG(0x00080000)
>> +		 LONG(0x80004000)
>> +		 /* Restart new PSW for booting via PSW restart. */
>> +		 . = 0x1a0;
>> +		 QUAD(0x0000000180000000)
>> +		 QUAD(0x0000000000004000)
>> +	}
>> +	. = 0x4000;
>> +	.text : {
>> +		*(.init)
>> +		*(.text)
>> +		*(.text.*)
>> +	}
>> +	. = ALIGN(64K);
>> +	etext = .;
>> +	.opd : { *(.opd) }
>> +	. = ALIGN(16);
>> +	.dynamic : {
>> +		dynamic_start = .;
>> +		*(.dynamic)
>> +	}
>> +	.dynsym : {
>> +		dynsym_start = .;
>> +		*(.dynsym)
>> +	}
>> +	.rela.dyn : { *(.rela*) }
>> +	. = ALIGN(16);
>> +	.data : {
>> +		*(.data)
>> +		*(.data.rel*)
>> +	}
>> +	. = ALIGN(16);
>> +	.rodata : { *(.rodata) *(.rodata.*) }
>> +	. = ALIGN(16);
>> +	__bss_start = .;
>> +	.bss : { *(.bss) }
>> +	__bss_end = .;
>> +	. = ALIGN(64K);
>> +	edata = .;
>> +	. += 64K;
>> +	. = ALIGN(64K);
>> +}
>>
>