[PATCH v3 1/4] efi: add EFI_SYSTEM_TABLE_POINTER for debug

[Paul Liu]

Hi Ilias,

On Mon, 26 May 2025 at 15:01, Ilias Apalodimas <ilias.apalodimas at linaro.org>
wrote:

> Hi Paul,
>
> [...]
>
>
> >         bool
> >
> > +config EFI_DEBUG_SUPPORT_TABLE
> > +       bool "EFI Debug Support Table"
> > +       help
> > +         Select this option if you want to setup the EFI Debug Support
> > +         Table which is used by the debug agent or an external debugger
> to
> > +         determine loaded image information in a quiescent manner.
> > +
> >  menu "UEFI services"
> >
> >  config EFI_GET_TIME
> > diff --git a/lib/efi_loader/efi_boottime.c
> b/lib/efi_loader/efi_boottime.c
> > index dbebb37dc04..5a4349f8679 100644
> > --- a/lib/efi_loader/efi_boottime.c
> > +++ b/lib/efi_loader/efi_boottime.c
> > @@ -4001,6 +4001,8 @@ struct efi_system_table __efi_runtime_data systab
> = {
> >         .tables = NULL,
> >  };
> >
> > +struct efi_system_table_pointer __efi_runtime_data * systab_pointer =
> NULL;
> > +
> >  /**
> >   * efi_initialize_system_table() - Initialize system table
> >   *
> > @@ -4035,3 +4037,47 @@ efi_status_t efi_initialize_system_table(void)
> >
> >         return ret;
> >  }
> > +
> > +/**
> > + * efi_initialize_system_table() - Initialize system table pointer
> > + *
> > + * Return:     status code
> > + */
> > +efi_status_t efi_initialize_system_table_pointer(void)
> > +{
> > +       efi_status_t ret;
> > +       const int size_4MB = 0x00400000;
> > +       int pages = efi_size_in_pages(sizeof(struct
> efi_system_table_pointer));
> > +       int alignment_mask = size_4MB - 1;
> > +       int real_pages = pages + efi_size_in_pages(size_4MB);
> > +       u64 addr;
> > +       u64 aligned_addr;
> > +       u32 crc32_value;
> > +
> > +       /* Allocate configuration table array */
> > +       ret = efi_allocate_pages(EFI_ALLOCATE_ANY_PAGES,
> > +                                EFI_RUNTIME_SERVICES_DATA,
> > +                                real_pages,
> > +                                &addr);
> > +
> > +       if (ret != EFI_SUCCESS) {
> > +               log_err("Installing EFI system table pointer failed\n");
> > +               return ret;
> > +       }
> > +
> > +       /* alignment to 4MB boundary */
> > +       aligned_addr = (addr + alignment_mask) & ~alignment_mask;
>
> efi_alloc_aligned_pages() does that for you.
> But I have similar questions to Heinrich here. Why do you need 4MB?


The alignment of this structure is 4MB. Is there a way not to allocate a
full page but still fulfill this?
The spec said. "A check-summed structure containing the physical address of
the EFI system table is created and located on a
4M aligned memory address. A hardware debugger can search memory for this
structure to determine the location of the EFI system table."

So that's why I need a page aligned with 4MB. This code is actually copied
from edk2. So I should replace it with efi_alloc_aligned_pages() right?


>

> > +
> > +       systab_pointer = (struct efi_system_table_pointer *)aligned_addr;
> > +       memset(systab_pointer, 0, sizeof(struct
> efi_system_table_pointer));
> > +
> > +       systab_pointer->signature = EFI_SYSTEM_TABLE_SIGNATURE;
> > +       systab_pointer->efi_system_table_base =
> (efi_physical_addr_t)&systab;
> > +       systab_pointer->crc32 = 0;
>
> You are assigning this at the end regardless, so I guess you can skip it
> here.
>
>
Will remove.


> > +       crc32_value = crc32(0,
> > +                           (const unsigned char *)systab_pointer,
> > +                           sizeof(struct efi_system_table_pointer));
> > +       systab_pointer->crc32 = crc32_value;
> > +
> > +       return ret;
> > +}
> > diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c
> > index 48f91da5df7..a6b37d994f6 100644
> > --- a/lib/efi_loader/efi_setup.c
> > +++ b/lib/efi_loader/efi_setup.c
> > @@ -278,6 +278,14 @@ efi_status_t efi_init_obj_list(void)
> >         if (ret != EFI_SUCCESS)
> >                 goto out;
> >
> > +       /* Initialize system table pointer */
> > +       if (IS_ENABLED(CONFIG_EFI_DEBUG_SUPPORT_TABLE)) {
> > +               ret = efi_initialize_system_table_pointer();
> > +               if (ret != EFI_SUCCESS) {
> > +                       goto out;
> > +               }
> > +       }
> > +
> >         if (IS_ENABLED(CONFIG_EFI_ECPT)) {
> >                 ret = efi_ecpt_register();
> >                 if (ret != EFI_SUCCESS)
> > --
> > 2.39.5
> >
>
> Thanks
> /Ilias
>