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List: linux-efi
Subject: [PATCH 8/8] Documentation/x86/boot: Correct segment requirements for 64-bit boot
From: Arvind Sankar <nivedita () alum ! mit ! edu>
Date: 2020-01-30 20:04:40
Message-ID: 20200130200440.1796058-9-nivedita () alum ! mit ! edu
[Download RAW message or body]
64-bit mode has no segment/GDT requirements as it does not really use
segment registers. The entry code loads null descriptors into the data
and stack segment registers.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
Documentation/x86/boot.rst | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)
diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst
index 3e13b7d57271..df2bf8abbbc1 100644
--- a/Documentation/x86/boot.rst
+++ b/Documentation/x86/boot.rst
@@ -1396,12 +1396,9 @@ In 64-bit boot protocol, the kernel is started by jumping to the
At entry, the CPU must be in 64-bit mode with paging enabled.
The range with setup_header.init_size from start address of loaded
kernel and zero page and command line buffer get ident mapping;
-a GDT must be loaded with the descriptors for selectors
-__BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat
-segment; __BOOT_CS must have execute/read permission, and __BOOT_DS
-must have read/write permission; CS must be __BOOT_CS and DS, ES, SS
-must be __BOOT_DS; interrupt must be disabled; %rsi must hold the base
-address of the struct boot_params.
+interrupt must be disabled; %rsi must hold the base address of the
+struct boot_params. As 64-bit mode does not really use segments, there
+are no special requirements on the segment registers or descriptors.
EFI Handover Protocol
=====================
--
2.24.1
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