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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-10-26 at 16:03 +0000, Anthony PERARD wrote:
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> ---
> Âtools/firmware/hvmloader/hvmloader.c | 69
> +++++++++++++++++++++++++++++++++++-
> Â1 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 (
> ÂÂÂÂÂ"ÂÂÂÂmovÂÂ%ax,%ssÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\n"
> ÂÂÂÂÂ/* Initialise all 32-bit GPRs to zero. */
> ÂÂÂÂÂ"ÂÂÂÂxorÂÂ%eax,%eaxÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\n"
> -ÂÂÂÂ"ÂÂÂÂxorÂÂ%ebx,%ebxÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\n"
> +ÂÂÂÂ/* 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.

> ÂÂÂÂÂ"ÂÂÂÂxorÂÂ%ecx,%ecxÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\n"
> ÂÂÂÂÂ"ÂÂÂÂxorÂÂ%edx,%edxÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\n"
> ÂÂÂÂÂ"ÂÂÂÂxorÂÂ%esp,%espÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\n"
> @@ -249,15 +249,82 @@ static void acpi_enable_sci(void)
> ÂÂÂÂÂBUG_ON(!(pm1a_cnt_val & ACPI_PM1C_SCI_EN));
> Â}
> Â
> +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.

> Âint main(void)
> Â{
> ÂÂÂÂÂconst struct bios_config *bios;
> ÂÂÂÂÂint acpi_enabled;
> +ÂÂÂÂconst struct hvm_start_info *hvmlite_start_info;
> +
> +ÂÂÂÂ/* Load hvmlite start info pointer from ebx. */
> +ÂÂÂÂasm 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.

> Â
> ÂÂÂÂÂ/* Initialise hypercall stubs with RET, rendering them no-ops. */
> ÂÂÂÂÂmemset((void *)HYPERCALL_PHYSICAL_ADDRESS, 0xc3 /* RET */,
> PAGE_SIZE);
> Â
> ÂÂÂÂÂprintf("HVM Loader\n");
> +ÂÂÂÂBUG_ON(hvmlite_start_info->magic != HVM_START_MAGIC_VALUE);
> +ÂÂÂÂprintf("cmdline: %s\n", (char*)hvmlite_start_info->cmdline_paddr);
> +ÂÂÂÂcmdline_parser((char*)hvmlite_start_info->cmdline_paddr);
> Â
> ÂÂÂÂÂinit_hypercalls();
> Â
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