Re: [Qemu-devel] [PATCH v2 1/1] s390x/ipl: Try to detect Linux vs non Linux for initial IPL PSW

[Thomas Huth]

On 11.06.2018 15:52, Christian Borntraeger wrote:
> Right now the IPL device always starts from address 0x10000 (the usual
> Linux entry point). To run other guests (e.g. test programs) it is
> useful to use the IPL PSW from address 0. We can use the Linux magic
> at 0x10008 to decide.
> 
> Signed-off-by: Christian Borntraeger <address@hidden>
> ---
> v1->v2:
>       - use LINUX_MAGIC_ADDR define
>       - use assert for valid iplpsw pointer
>       - add endianess conversion
>  hw/s390x/ipl.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/s390x/ipl.c b/hw/s390x/ipl.c
> index 04245b5258..3790153fa9 100644
> --- a/hw/s390x/ipl.c
> +++ b/hw/s390x/ipl.c
> @@ -29,6 +29,7 @@
>  #include "exec/exec-all.h"
>  
>  #define KERN_IMAGE_START                0x010000UL
> +#define LINUX_MAGIC_ADDR                0x010008UL
>  #define KERN_PARM_AREA                  0x010480UL
>  #define INITRD_START                    0x800000UL
>  #define INITRD_PARM_START               0x010408UL
> @@ -105,7 +106,9 @@ static uint64_t bios_translate_addr(void *opaque, 
> uint64_t srcaddr)
>  static void s390_ipl_realize(DeviceState *dev, Error **errp)
>  {
>      S390IPLState *ipl = S390_IPL(dev);
> -    uint64_t pentry = KERN_IMAGE_START;
> +    uint64_t *iplpsw;
> +    uint64_t pentry;
> +    char *magic;
>      int kernel_size;
>      Error *err = NULL;
>  
> @@ -157,6 +160,16 @@ static void s390_ipl_realize(DeviceState *dev, Error 
> **errp)
>                                 NULL, 1, EM_S390, 0, 0);
>          if (kernel_size < 0) {
>              kernel_size = load_image_targphys(ipl->kernel, 0, ram_size);
> +            /* if this is Linux use KERN_IMAGE_START */
> +            magic = rom_ptr(LINUX_MAGIC_ADDR);
> +            if (magic && !memcmp(magic, "S390EP", 6)) {
> +                pentry = KERN_IMAGE_START;
> +            } else {
> +                /* if not Linux use the IPL PSW */
> +                iplpsw = rom_ptr(0);
> +                assert(iplpsw);

Hmm, wait, what if load_image_targphys() failed and returned a
kernel_size < 0 ... won't we hit that assert() in that case? I think you
might want to check for kernel_size > 0 (or even > 8) here first.

> +                pentry = be64_to_cpu(*iplpsw) & 0x7fffffffUL;
> +            }
>          }
>          if (kernel_size < 0) {
>              error_setg(&err, "could not load kernel '%s'", ipl->kernel);
> 

 Thomas