From: Rich Felker <dalias@aerifal.cx>
Date: Mon, 25 Apr 2016 23:37:06 +0000 (-0400)
Subject: fix thread structure/dtv-pointer corruption on powerpc
X-Git-Tag: v1.1.15~67
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=be999f7a54e81656ea0409030205177327a7450c;p=musl

fix thread structure/dtv-pointer corruption on powerpc

per the powerpc psabi, offset 4 of the stack at call time belongs to
the callee and is used for spilling lr (return address). in addition,
offset 0 on the stack must contain a pointer to the previous stack
frame, or a null pointer for the initial stack frame of a thread.
__clone failed to setup any stack frame on the new thread's stack,
thereby allowing the start function it called to clobber offset 4 of
the new thread's struct __pthread, which contains the dtv pointer.

add code to setup a proper stack frame and align the stack pointer to
a multiple of 16 (also an abi requirement) if it was not already
aligned.
---

diff --git a/src/thread/powerpc/clone.s b/src/thread/powerpc/clone.s
index dc5c74c6..a57dbcce 100644
--- a/src/thread/powerpc/clone.s
+++ b/src/thread/powerpc/clone.s
@@ -22,6 +22,11 @@ stw 31, 4(1)
 mr 30, 3
 mr 31, 6
 
+# create initial stack frame for new thread
+clrrwi 4, 4, 4
+li 0, 0
+stwu 0, -16(4)
+
 #move c into first arg
 mr 3, 5
 #mr 4, 4