[PARISC] Document some register usages in assembly files
Document clobbers and args in entry.S and syscall.S.
entry.S: Add comment to indicate that cr27 may recycle and EDEADLOCK
detection is not 100% correct. Since this is only enabled when using
ENABLE_LWS_DEBUG, the user is warned by the comment.
Signed-off-by: Carlos O'Donell <carlos@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>
diff --git a/arch/parisc/kernel/entry.S b/arch/parisc/kernel/entry.S
index c7e66ee..9af4b22 100644
--- a/arch/parisc/kernel/entry.S
+++ b/arch/parisc/kernel/entry.S
@@ -1846,6 +1846,7 @@
ldo -16(%r30),%r29 /* Reference param save area */
#endif
+ /* WARNING - Clobbers r19 and r21, userspace must save these! */
STREG %r2,PT_GR19(%r1) /* save for child */
STREG %r30,PT_GR21(%r1)
BL sys_clone,%r2
diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index b29b76b4..d661634 100644
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -164,7 +164,7 @@
#endif
STREG %r2, TASK_PT_GR30(%r1) /* ... and save it */
- STREG %r20, TASK_PT_GR20(%r1)
+ STREG %r20, TASK_PT_GR20(%r1) /* Syscall number */
STREG %r21, TASK_PT_GR21(%r1)
STREG %r22, TASK_PT_GR22(%r1)
STREG %r23, TASK_PT_GR23(%r1) /* 4th argument */
@@ -527,6 +527,7 @@
We *must* giveup this call and fail.
*/
ldw 4(%sr2,%r20), %r28 /* Load thread register */
+ /* WARNING: If cr27 cycles to the same value we have problems */
mfctl %cr27, %r21 /* Get current thread register */
cmpb,<>,n %r21, %r28, cas_lock /* Called recursive? */
b lws_exit /* Return error! */