x86: Use fs for global data
Use the base address of the 'F' segment as a pointer to the global data
structure. By adding the linear address (i.e. the 'D' segment address) as
the first word of the global data structure, the address of the global data
relative to the 'D' segment can be found simply, for example, by:
fs movl 0, %eax
This makes the gd 'pointer' writable prior to relocation (by reloading the
Global Desctriptor Table) which brings x86 into line with all other arches
NOTE: Writing to the gd 'pointer' is expensive (but we only do it
twice) but using it to access global data members (read and write) is
still fairly cheap
--
Changes for v2:
- Rebased against changes made to patch #3
- Removed extra indent
- Tweaked commit message
diff --git a/arch/x86/include/asm/global_data.h b/arch/x86/include/asm/global_data.h
index 05a2139..908a02c 100644
--- a/arch/x86/include/asm/global_data.h
+++ b/arch/x86/include/asm/global_data.h
@@ -36,6 +36,8 @@
#ifndef __ASSEMBLY__
typedef struct global_data {
+ /* NOTE: gd_addr MUST be first member of struct global_data! */
+ unsigned long gd_addr; /* Location of Global Data */
bd_t *bd;
unsigned long flags;
unsigned long baudrate;
@@ -51,13 +53,24 @@
unsigned long bus_clk;
unsigned long relocaddr; /* Start address of U-Boot in RAM */
unsigned long start_addr_sp; /* start_addr_stackpointer */
+ unsigned long gdt_addr; /* Location of GDT */
+ unsigned long new_gd_addr; /* New location of Global Data */
phys_size_t ram_size; /* RAM size */
unsigned long reset_status; /* reset status register at boot */
void **jt; /* jump table */
char env_buf[32]; /* buffer for getenv() before reloc. */
} gd_t;
-extern gd_t *gd;
+static inline gd_t *get_fs_gd_ptr(void)
+{
+ gd_t *gd_ptr;
+
+ asm volatile("fs movl 0, %0\n" : "=r" (gd_ptr));
+
+ return gd_ptr;
+}
+
+#define gd get_fs_gd_ptr()
#endif
@@ -73,12 +86,6 @@
#define GD_FLG_DISABLE_CONSOLE 0x00040 /* Disable console (in & out) */
#define GD_FLG_ENV_READY 0x00080 /* Environment imported into hash table */
-#if 0
#define DECLARE_GLOBAL_DATA_PTR
-#else
-#define XTRN_DECLARE_GLOBAL_DATA_PTR extern
-#define DECLARE_GLOBAL_DATA_PTR XTRN_DECLARE_GLOBAL_DATA_PTR \
-gd_t *gd
-#endif
#endif /* __ASM_GBL_DATA_H */