From: alad@hss.hns.com
To: linux-kernel@vger.kernel.org
Message-ID: <65256A26.0027EA80.00@sandesh.hss.hns.com>
Date: Fri, 6 Apr 2001 12:53:10 +0530
Subject: __switch_to macro
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Sender: linux-kernel-owner@vger.kernel.org


Hi,
     The note above __switch_to macro in i386/kernel/process.c says that we no
more use hardware context switching as some problems in recovering from
saved state that is no longer valid. (I am peeking into 2.2 kernel). Now I have
following questions

1) What exactly is meant by ' stale segment register values' in the note.
2) In the above macro, I think we recover gracefully from error condition while
recovering fs and gs segment registers . The loadsegment(fs,next->tss.fs) and
loadsegment(gs,next->tss.gs) does it. I am not able to understand loadsegment
macro. The macro is as under

/** Load a segment. Fall back on loading a zero segment if something goes wrong
**/
#define loadsegment(seg,value)           \
     asm volatile("\n"             \
          "1:\t"                   \
          "movl %0,%%" #seg "\n"   \
          "2:\n"                   \
          "3:\t"                   \
          "pushl $0\n\t"           \
          "jmp 2b\n"               \
          ".previous\n"            \
          ".section __ex_table,\"a\"\n\t  \
          "/align 4\n\t"           \
          ".long 1b,3b\n"          \
          ".previous"              \
          : :"m" (*(unsigned int *)&(value)))

I also want to know what is 'something' in the comment above the macro

Thanks in advance
Amol


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