lkml.org 
[lkml]   [2019]   [Jan]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH v15 3/6] x86/boot: Introduce efi_get_rsdp_addr() to find RSDP from EFI table
    On Fri, Jan 11, 2019 at 11:32:25AM +0100, Borislav Petkov wrote:
    >On Fri, Jan 11, 2019 at 09:23:53AM +0800, Chao Fan wrote:
    >> Yes, 'table64' looks superfluous here, but after these lines, there is:
    >> if (!IS_ENABLED(CONFIG_X86_64) && table64 >> 32) {
    >> so the 'table64' is useful here for i386. 'table' is unsigned long, it
    >> can't do the right shift. But the 'table64' who is u64 can do that right
    >> shift.
    >
    >Have you actually tried fixing what I suggested or you're just talking?

    Sure, I tried what I was talking.
    I ever used 'unsigned long table' directly. But that caused warning:
    CC arch/x86/boot/compressed/acpi.o
    arch/x86/boot/compressed/acpi.c: In function ‘efi_get_rsdp_addr’:
    arch/x86/boot/compressed/acpi.c:106:44: warning: right shift count >= width of type [-Wshift-count-overflow]
    if (!IS_ENABLED(CONFIG_X86_64) && table >> 32) {
    To avoid this warning, I add 'u64 table64' to do the right shift.

    Well, the acpi_physicall_address defined as:

    #if ACPI_MACHINE_WIDTH == 64
    typedef u64 acpi_physical_address;
    #elif ACPI_MACHINE_WIDTH == 32
    #ifdef ACPI_32BIT_PHYSICAL_ADDRESS
    typedef u32 acpi_physical_address;
    #else /* ACPI_32BIT_PHYSICAL_ADDRESS */

    /*
    * It is reported that, after some calculations, the physical addresses
    can
    * wrap over the 32-bit boundary on 32-bit PAE environment.
    * https://bugzilla.kernel.org/show_bug.cgi?id=87971
    */
    typedef u64 acpi_physical_address;
    #endif

    'acpi_physical_address' could be define as u64 or u32.
    In my guest machine, it's defined as u64, there is no problem as you
    suggested.
    I didn't find a machine where 'acpi_physical_address' defined as u32.
    I thought if 'acpi_physical_address' defined as u32, it will meet
    the same warning as using 'unsigned long'.
    I tried to define 'table' as u32, that will also cause the warning.
    So once acpi_physical_address is define as u32, that warning will
    happen. We should make sure u64 to do the right shift.

    Thanks,
    Chao Fan

    >
    >---
    >diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
    >index e9dd84f459ed..0537d46fb21f 100644
    >--- a/arch/x86/boot/compressed/acpi.c
    >+++ b/arch/x86/boot/compressed/acpi.c
    >@@ -77,21 +77,19 @@ static acpi_physical_address efi_get_rsdp_addr(void)
    > sizeof(efi_config_table_32_t);
    >
    > for (i = 0; i < systab->nr_tables; i++) {
    >+ acpi_physical_address table;
    > void *config_tables;
    >- unsigned long table;
    > efi_guid_t guid;
    >
    > config_tables = (void *)(systab->tables + size * i);
    > if (efi_64) {
    > efi_config_table_64_t *tmp_table;
    >- u64 table64;
    >
    > tmp_table = config_tables;
    > guid = tmp_table->guid;
    >- table64 = tmp_table->table;
    >- table = table64;
    >+ table = tmp_table->table;
    >
    >- if (!IS_ENABLED(CONFIG_X86_64) && table64 >> 32) {
    >+ if (!IS_ENABLED(CONFIG_X86_64) && table >> 32) {
    > debug_putstr("Error getting RSDP address: EFI config table located above 4GB.\n");
    > return 0;
    > }
    >
    >--
    >Regards/Gruss,
    > Boris.
    >
    >Good mailing practices for 400: avoid top-posting and trim the reply.
    >
    >


    \
     
     \ /
      Last update: 2019-01-13 10:49    [W:4.145 / U:0.836 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site