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[MIPS] Fix $gp usage

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Now we load $gp with _GLOBAL_OFFSET_TABLE_, but this is incorrect use.
As a general principle, we should use _gp for $gp.

Thanks to linker script's help we fortunately have _gp which equals to
_GLOBAL_OFFSET_TABLE_. But once _gp gets out of alignment, we will not
be able to access to GOT entires, global variables and procedure entry
points. The right thing to do is to use _gp.

This patch also introduce a new symbol `.gpword _GLOBAL_OFFSET_TABLE_'
which holds the offset from _gp. When updating GOT entries, we use this
offset and _gp to calculate the final _GLOBAL_OFFSET_TABLE_.

This patch is originally submitted by Vlad Lungu <vlad@comsys.ro>, then
I made some change to leave over num_got_entries.

Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi@necel.com>
Cc: Vlad Lungu <vlad@comsys.ro>
This commit is contained in:
Shinya Kuribayashi 2007-10-21 10:55:36 +09:00 committed by Shinya Kuribayashi
parent cbf2323b5b
commit 22069215eb
1 changed files with 13 additions and 6 deletions
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19
cpu/mips/start.S
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@ -234,11 +234,11 @@ reset:
li t0, CONF_CM_UNCACHED
mtc0 t0, CP0_CONFIG
/* Initialize GOT pointer.
/* Initialize $gp.
*/
bal 1f
nop
.word _GLOBAL_OFFSET_TABLE_
.word _gp
1:
move gp, ra
lw t1, 0(ra)
@ -306,9 +306,9 @@ relocate_code:
move t1, a2
/*
* Fix GOT pointer:
* Fix $gp:
*
* New GOT-PTR = (old GOT-PTR - CFG_MONITOR_BASE) + Destination Address
* New $gp = (Old $gp - CFG_MONITOR_BASE) + Destination Address
*/
move t6, gp
sub gp, CFG_MONITOR_BASE
@ -341,15 +341,22 @@ relocate_code:
j t0
nop
.gpword _GLOBAL_OFFSET_TABLE_ /* _GLOBAL_OFFSET_TABLE_ - _gp */
.word uboot_end_data
.word uboot_end
.word num_got_entries
in_ram:
/* Now we want to update GOT.
/*
* Now we want to update GOT.
*
* GOT[0] is reserved. GOT[1] is also reserved for the dynamic object
* generated by GNU ld. Skip these reserved entries from relocation.
*/
lw t3, -4(t0) /* t3 <-- num_got_entries */
addi t4, gp, 8 /* Skipping first two entries. */
lw t4, -16(t0) /* t4 <-- (_GLOBAL_OFFSET_TABLE_ - _gp) */
add t4, t4, gp /* t4 now holds _GLOBAL_OFFSET_TABLE_ */
addi t4, t4, 8 /* Skipping first two entries. */
li t2, 2
1:
lw t1, 0(t4)