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authorOliver O'Halloran <oohall@gmail.com>2016-03-01 11:56:28 +1100
committerStewart Smith <stewart@linux.vnet.ibm.com>2016-03-07 13:48:49 +1100
commit1141ca0f74d9cf8dc8456f5ea9248e82b468d36b (patch)
tree4987648f4696a9e22cef2a1b724cd206179754a0
parent1325599645ff46b0c767ef23ee8a36c0c7a4d13f (diff)
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asm/head.S: fix hang in multi-threaded mambo
In very early boot, skiboot places secondary threads in holding loop until the primary thread has finished relocating skiboot. The secondary threads wait until a flag at INITAL_OFFSET + offsetof(boot_flag) is set to one before continuing. After relocating the skiboot image and applying ELF relocations the sets this flag and continues booting. To avoid having to copy skiboot at runtime within the simulation e605691e introduced a change to have the skiboot.tcl mambo script load skiboot at it's preferred location of 0x30000000 rather than 0x00000000. Unfortunately, the relocation code path is also responsible for saving the inital offset pointer (into r15). When not taken this results in the main thread writing to r15 + offsetof(boot_flag) instead, which leaves the secondary threads stuck waiting for boot_flag and the main thread stuck when trying to call-in the secondary threads during CPU initialisation. This patch fixes the bug by saving the inital offset before checking if relocation is necessary and adds a few comments to better document the relocation process. Signed-off-by: Oliver O'Halloran <oohall@gmail.com> Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
-rw-r--r--asm/head.S10
1 files changed, 9 insertions, 1 deletions
diff --git a/asm/head.S b/asm/head.S
index 6963188..192de55 100644
--- a/asm/head.S
+++ b/asm/head.S
@@ -308,6 +308,12 @@ boot_entry:
/* Initialize thread SPRs */
bl init_replicated_sprs
+ /* Save the initial offset. The secondary threads will spin on boot_flag
+ * before relocation so we need to keep track of its location to wake
+ * them up.
+ */
+ mr %r15,%r30
+
/* Check if we need to copy ourselves up and update %r30 to
* be our new offset
*/
@@ -317,17 +323,19 @@ boot_entry:
srdi %r3,%r3,3
mtctr %r3
mr %r4,%r30
- mr %r15,%r30
mr %r30,%r29
+ /* copy the skiboot image to the new offset */
1: ld %r0,0(%r4)
std %r0,0(%r29)
addi %r29,%r29,8
addi %r4,%r4,8
bdnz 1b
+ /* flush caches, etc */
sync
icbi 0,%r29
sync
isync
+ /* branch to the new image location and continue */
LOAD_IMM32(%r3, 2f - __head)
add %r3,%r3,%r30
mtctr %r3