work around mips detached thread exit breakage due to kernel regression

linux kernel commit 46e12c07b3b9603c60fc1d421ff18618241cb081 caused
the mips syscall mechanism to fail with EFAULT when the userspace
stack pointer is invalid, breaking __unmapself used for detached
thread exit. the workaround is to set $sp to a known-valid, readable
address, and the simplest one to obtain is the address of the current
function, which is available (per o32 calling convention) in $25.

diff --git a/src/thread/mips/__unmapself.s b/src/thread/mips/__unmapself.s
index 9aa03712bda91d3ff837742925bf9ad1f6d3fbf8..ba139dc8e7ba8d8672c1261c9391ca9da0f70524 100644 (file)
--- a/src/thread/mips/__unmapself.s
+++ b/src/thread/mips/__unmapself.s
@@ -2,6 +2,7 @@
 .global __unmapself
 .type   __unmapself,@function
 __unmapself:
+       move $sp, $25
        li $2, 4091
        syscall
        li $4, 0