Messages in this thread Patch in this message | | | Date | Sun, 13 Jan 2019 17:47:04 +0800 | From | Chao Fan <> | Subject | Re: [PATCH v15 3/6] x86/boot: Introduce efi_get_rsdp_addr() to find RSDP from EFI table |
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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. > >
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