On 18.12.18 10:26, Janosch Frank wrote:
> When doing an IPL normal the memory will not be zeroed and hence the
> BSS section can have any value. We need to clear it by ourselves.
>
> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
> ---
> s390x/cstart64.S | 21 ++++++++++++++++++++-
> s390x/flat.lds | 2 ++
> 2 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/s390x/cstart64.S b/s390x/cstart64.S
> index 7886f35..aba11f4 100644
> --- a/s390x/cstart64.S
> +++ b/s390x/cstart64.S
> @@ -37,6 +37,22 @@ start:
> /* setup initial PSW mask + control registers*/
> larl %r1, initial_psw
> lpswe 0(%r1)
> +init_clear_bss:
clear_bss_start ?
(to get better names for the other labels)
> + larl %r2, __bss_start
> + larl %r3, __bss_end
> + slgr %r3, %r2 # Get sizeof bss
> + aghi %r3,-1
> + srlg %r4,%r3,8 # Calc number of 256 byte chunks
> + ltgr %r4,%r4
> + lgr %r1,%r2
> + jz remainder # If none, clear remaining bytes
> +loop:
clear_bss_loop ?
> + xc 0(256,%r1), 0(%r1) # Clear 256 byte chunks via xor
> + la %r1, 256(%r1)
> + brctg %r4, loop
> +remainder:
clear_bss_remainder ?
> + larl %r2, memsetxc
> + ex %r3, 0(%r2)
> init_psw_cont:
We don't need this label anymore
> /* setup pgm interrupt handler */
> larl %r1, pgm_int_psw
> @@ -69,6 +85,9 @@ init_psw_cont:
> /* call exit() */
> j exit
>
> +memsetxc:
> + xc 0(1,%r1),0(%r1)
> +
I trust you on the clearing logic ;)
> .macro SAVE_REGS
> /* save grs 0-15 */
> stmg %r0, %r15, GEN_LC_SW_INT_GRS
> @@ -157,7 +176,7 @@ svc_int:
>
> .align 8
> initial_psw:
> - .quad 0x0000000180000000, init_psw_cont
> + .quad 0x0000000180000000, init_clear_bss
> pgm_int_psw:
> .quad 0x0000000180000000, pgm_int
> ext_int_psw:
> diff --git a/s390x/flat.lds b/s390x/flat.lds
> index 977af7c..403d967 100644
> --- a/s390x/flat.lds
> +++ b/s390x/flat.lds
> @@ -40,7 +40,9 @@ SECTIONS
> . = ALIGN(16);
> .rodata : { *(.rodata) *(.rodata.*) }
> . = ALIGN(16);
> + __bss_start = .;
> .bss : { *(.bss) }
> + __bss_end = .;
> . = ALIGN(64K);
> edata = .;
> . += 64K;
>
--
Thanks,
David / dhildenb
