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Re: Unix V6 : Sample C to 65c02 translation from 'sh'

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wssimms wrote:
> I've started working on translating the Unix V6 sh to 65c02 assembler.
> This shell is called the Thompson shell because it was written by Ken
> Thompson. It is less sophisticated than the Bourne Shell that was
> included in 7th Edition Unix, but it's actually more complicated than
> I thought because the last time I looked at shell source (about 9 months
> ago), I was looking at the 1st Edition Unix shell.
> 
> The 6th Edition shell is written in C and includes a recursive descent
> parser for the (very simple) command language it accepts. Here is one
> of the parse functions. There is an array of pointers to char called
> args[] that contains the tokens of the input line. The pointers p1 & p2
> being passed into syn1, are pointers to the first and last+1 elements
> of args[] that are to be parsed by this function (i.e, they delimit a
> subrange of the tokenized input line)
> 
> The purpose of this function is to find expression delimiters in the
> input line and build a list of parse subtrees of the expressions between
> the delimiters. The result is a pointer to a tree node consisting of
> four words: a type, flags, a pointer to a left subtree, and a pointer to
> a right subtree. The chain of right-subtree links represents the list
> of delimited expresssions.
> 
> The possible delimiters are ';', which results in sequential execution
> of the subexpressions, and '&', which results in background execution
> of the preceding subexpression. This should be pretty familiar to most
> people. Here's the C code from 6th Edition Unix
> (snip)
a) Should the code extract below
2:	inx
	inx                        // advance to next arg
	bra        9b
1:	cmp        #'&'
	beq        2f
	cmp        #';'
	beq        2f
	cmp        #'\n'
	bne        2b                // if not '&' ';' '\n' advance to next arg
2:	lda        parcnt                // if nesting depth is nonzero
	bne        2b                // advance to next arg
read
2:	inx
	inx                        // advance to next arg
	bra        9b
1:	cmp        #'&'
	beq        1f
	cmp        #';'
	beq        1f
	cmp        #'\n'
	bne        2b                // if not '&' ';' '\n' advance to next arg
1:
	lda        parcnt                // if nesting depth is nonzero
	bne        2b                // advance to next arg
instead? otherwise there might be an infinite loop within the current
process?

b) Your code seems to use self modifying tricks (bytes at addresse 9:+1 and
8:+1), beware  if an interrupt occured after those addressed are updated but
before they are accessed again within the code. But I might be wrong if your
code is considered private and stored into a dedicated (i.e. not shared)
segment to the current process.


-- 
Growing old is mandatory..
growing up is optional..
But the other way round is as true.

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Unix V6 : Sample C to 65c02 translation from 'sh' wssimms@gmail.com - 2016-03-28 21:32 -0700
  Re: Unix V6 : Sample C to 65c02 translation from 'sh' Benoit0123 <bgilon@free.fr> - 2016-03-29 12:56 +0000
    Re: Unix V6 : Sample C to 65c02 translation from 'sh' wssimms@gmail.com - 2016-03-29 06:56 -0700

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