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Date: Tue, 3 Mar 2015 11:49:31 +0800
From: chenfeng <puck.chen@...ilicon.com>
To: "punit.agrawal" <punit.agrawal@....com>
CC: <"catalin.marinas"@arm.com>, <will.deacon@....com>,
<linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>,
"Peter Panshilin" <peter.panshilin@...ilicon.com>,
Suzhuangluan <suzhuangluan@...ilicon.com>,
Yiping Xu <xuyiping@...ilicon.com>,
Dan zhao <dan.zhao@...ilicon.com>,
qijiwen <qijiwen@...ilicon.com>,
Wangbintian <bintian.wang@...wei.com>
Subject: Alignment issue with ldmia
There is an alignment issue with ldmia in A32 user-space with A64
Kernel. Since the famous taobao apk use this instruction, so we want to
emulate this to make it work well.
I make a simple test case to reproduce this issue.
-----------------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
int main()
{
char src_addr[1024];
char dst_addr[1024];
printf("--------%lx %lx\n",src_addr,dst_addr);
unsigned long src_reg = (unsigned long)src_addr | 1;
unsigned long dst_reg = (unsigned long)dst_addr | 1;
printf("--------%lx %lx\n",src_reg,dst_reg);
asm volatile("mov r1, %0\n": : "r" (src_reg));
asm volatile("mov r2, %0\n": : "r" (dst_reg));
asm volatile("ldmia r1!,{r2}");
printf("--------------------------\n");
return 0;
}
------------------------------------------------------------------------
I use the test case on A32 kernel with A32 user-space. It works
well,becase of that is a do_alignment_ldmstm emulate in
arch/arm/mm/alignment.c
So, I want to porting the code to arch/arm64.
The first step is getting the machine code of the unalignment
instruction. However I have no idea how to do this.
There is a commit on google master L branch to emulate the undef
instruction. I use these code for getting the instruction of unalignment
case. But I found the code in arch/arm/alignment.c get the instruction
is 0xe8b10004 and the code in arch/arm64/kernel/traps.c is different.
Since I arm not professional for the code, I am writting for asking is
there a way to get the thumb instruction when traps in kernel mode.
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