Re: [RFC PATCH v2 07/16] hvmloader: Grab the hvmlite info page and parse the cmdline

[Ian Campbell <ian.campbell@citrix.com>]

On Mon, 2015-10-26 at 16:03 +0000, Anthony PERARD wrote:
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> ---
>  tools/firmware/hvmloader/hvmloader.c | 69
> +++++++++++++++++++++++++++++++++++-
>  1 file changed, 68 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/firmware/hvmloader/hvmloader.c
> b/tools/firmware/hvmloader/hvmloader.c
> index 716d03c..9df12ac 100644
> --- a/tools/firmware/hvmloader/hvmloader.c
> +++ b/tools/firmware/hvmloader/hvmloader.c
> @@ -62,7 +62,7 @@ asm (
>      "    mov  %ax,%ss                \n"
>      /* Initialise all 32-bit GPRs to zero. */
>      "    xor  %eax,%eax              \n"
> -    "    xor  %ebx,%ebx              \n"
> +    /* Keep ebx, for HVMLite start info */

Isn't this now an ABI between the tools and HVM loader, which is embedded
in the more formal PVH/HVMLite startup protocol? In which case hopefully
there is somewhere it can be documented. Is a HVMlite/PVH guest allowed to
assume anything about %ebx, those sorts of questions need to be considered.

>      "    xor  %ecx,%ecx              \n"
>      "    xor  %edx,%edx              \n"
>      "    xor  %esp,%esp              \n"
> @@ -249,15 +249,82 @@ static void acpi_enable_sci(void)
>      BUG_ON(!(pm1a_cnt_val & ACPI_PM1C_SCI_EN));
>  }
>  
> +static const char *module_list_order = NULL;
> +void cmdline_parser(const char *the_cmdline)

I'll leave this until we've decided if this approach is the one we want.

>  int main(void)
>  {
>      const struct bios_config *bios;
>      int acpi_enabled;
> +    const struct hvm_start_info *hvmlite_start_info;
> +
> +    /* Load hvmlite start info pointer from ebx. */
> +    asm volatile ( "mov %%ebx,%0" : "=r" (hvmlite_start_info) );

The stub which calls main should perhaps arrange for this to be in a
register which ends up being a parameter to this struct. I think otherwise
nothing ensures that the function prolog hasn't clobbered %ebx already.

>  
>      /* Initialise hypercall stubs with RET, rendering them no-ops. */
>      memset((void *)HYPERCALL_PHYSICAL_ADDRESS, 0xc3 /* RET */,
> PAGE_SIZE);
>  
>      printf("HVM Loader\n");
> +    BUG_ON(hvmlite_start_info->magic != HVM_START_MAGIC_VALUE);
> +    printf("cmdline: %s\n", (char*)hvmlite_start_info->cmdline_paddr);
> +    cmdline_parser((char*)hvmlite_start_info->cmdline_paddr);
>  
>      init_hypercalls();
>  
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