From: Shinya Kuribayashi shinya.kuribayashi@necel.com
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 ---
cpu/mips/start.S | 19 +++++++++++++------ 1 files changed, 13 insertions(+), 6 deletions(-)
diff --git a/cpu/mips/start.S b/cpu/mips/start.S index e91e213..074d01d 100644 --- a/cpu/mips/start.S +++ b/cpu/mips/start.S @@ -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)