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

[Ian Campbell]

On Mon, 2015-10-26 at 16:03 +, Anthony PERARD wrote:
> Signed-off-by: Anthony PERARD 
> ---
>  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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[Xen-devel] [RFC PATCH v2 07/16] hvmloader: Grab the hvmlite info page and parse the cmdline

[Anthony PERARD]

Signed-off-by: Anthony PERARD 
---
 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 */
 "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)
+{
+char cmdline[MAX_GUEST_CMDLINE];
+char *p, *q;
+char *optval;
+
+strncpy(cmdline, the_cmdline, sizeof (cmdline));
+cmdline[MAX_GUEST_CMDLINE-1] = '\0';
+
+for ( p = cmdline; p < (cmdline + MAX_GUEST_CMDLINE) && *p; p++ )
+{
+if ( *p == ' ' )
+continue;
+
+/* search for the end of the parameter name */
+for ( q = p; *q && *q != '=' && *q != ' '; q++ )
+;
+
+/* search for the end of the optional paremeter value */
+if ( *q == '=' )
+{
+optval = q+1;
+if (*optval == '\0' || *optval == ' ') {
+optval = NULL;
+}
+} else
+optval = NULL;
+*q = '\0';
+
+if ( optval )
+{
+for ( q = optval; *q && *q != ' '; q++ )
+;
+*q = '\0';
+}
+
+/* compare known parameters */
+if ( !strcmp(p, "modules") )
+{
+printf("  cmdline: found '%s', with val '%s'\n", p, optval);
+if ( optval )
+{
+unsigned size = strlen(optval) + 1;
+char *tmp = scratch_alloc(size, 0);
+strncpy(tmp, optval, size);
+module_list_order = tmp;
+}
+} else {
+printf("  Unknown cmdline option '%s'", p);
+if ( optval )
+printf(" with val '%s'\n", optval);
+else
+printf("\n");
+}
+
+p = q;
+}
+}
+
 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) );
 
 /* 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();
 
-- 
Anthony PERARD


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