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Re: [Tinycc-devel] Bug: array references with long long ints on i386

From: Thomas Preud'homme
Subject: Re: [Tinycc-devel] Bug: array references with long long ints on i386
Date: Wed, 11 Jul 2012 23:44:47 +0200
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Grishka and Daniel, please see below.

Here is the patch (see attached file).

So the thing is during gv() on a long long on i386 at some point the vstack 
contains at the top 2 values like this:

  register r contains the address of the value to load
  register r2 can contain anything (can be a valid register)
  register r contains the most significant bits of the value
  register r2 can contain anything (same value as in vtop)

get_reg tries first to free r before r2 so if r2 is a valid register, get_reg 
will try to free a register and the first one it will find to free is the 
register r of vtop-1 which leads to the bug. It's possible in gv to ignore how 
get_reg works but that requires a for loop to retry until get_reg returns 2 
differents registers. The other solution is to ensure that get_reg tries r2 
first, which is what the patch does.

Grishka and Daniel, do you know any place in the code which could rely on the 
previous behavior of get_reg()? If yes please revert the commit 

Best regards,

Thomas Preud'homme

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