Start documenting Configure internals
This is a living document, everyone is encouraged to add to it. Implementation details as well as broader implementation philosophy has a place here. I'm starting with documentation of the how conditions in build.info files are treated. Reviewed-by: Rich Salz <rsalz@openssl.org>
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Richard Levitte
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Configurations/INTERNALS.Configure
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Configurations/INTERNALS.Configure
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Configure Internals
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===================
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[ note: this file uses markdown for formatting ]
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Intro
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-----
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This is a collection of notes that are hopefully of interest to those
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who decide to dive into Configure and what it does. This is a living
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document and anyone is encouraged to add to it and submit changes.
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There's no claim for this document to be complete at any time, but it
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will hopefully reach such a point in time.
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----------------------------------------------------------------------
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Parsing build.info files, processing conditions
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-----------------------------------------------
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Processing conditions in build.info files is done with the help of a
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condition stack that tell if a build.info should be processed or if it
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should just be skipped over. The possible states of the stack top are
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expressed in the following comment from Configure:
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# The top item of this stack has the following values
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# -2 positive already run and we found ELSE (following ELSIF should fail)
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# -1 positive already run (skip until ENDIF)
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# 0 negatives so far (if we're at a condition, check it)
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# 1 last was positive (don't skip lines until next ELSE, ELSIF or ENDIF)
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# 2 positive ELSE (following ELSIF should fail)
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Ground rule is that non-condition lines are skipped over if the
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stack top is > 0. Condition lines (IF, ELSIF, ELSE and ENDIF
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statements) need to be processed either way to keep track of the skip
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stack states, so they are a little more intricate.
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Instead of trying to describe in words, here are some example of what
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the skip stack should look like after each line is processed:
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Example 1:
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| IF[1] | 1 | |
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| ... whatever ... | | this line is processed |
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| IF[1] | 1 1 | |
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| ... whatever ... | | this line is processed |
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| ELSIF[1] | 1 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSE | 1 -2 | |
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| ... whatever ... | | this line is skipped over |
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| ENDIF | 1 | |
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| ... whatever ... | | this line is processed |
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| ELSIF[1] | -1 | |
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| ... whatever ... | | this line is skipped over |
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| IF[1] | -1 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSIF[1] | -1 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSE | -1 -2 | |
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| ... whatever ... | | this line is skipped over |
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| ENDIF | -1 | |
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| ... whatever ... | | this line is skipped over |
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| ENDIF | | |
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Example 2:
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| IF[0] | 0 | |
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| ... whatever ... | | this line is skipped over |
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| IF[1] | 0 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSIF[1] | 0 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSE | 0 -2 | |
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| ... whatever ... | | this line is skipped over |
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| ENDIF | 0 | |
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| ... whatever ... | | this line is skipped over |
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| ELSIF[1] | 1 | |
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| ... whatever ... | | this line is processed |
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| IF[1] | 1 1 | |
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| ... whatever ... | | this line is processed |
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| ELSIF[1] | 1 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSE | 1 -2 | |
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| ... whatever ... | | this line is skipped over |
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| ENDIF | 1 | |
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| ... whatever ... | | this line is processed |
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| ENDIF | | |
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Example 3:
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| IF[0] | 0 | |
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| ... whatever ... | | this line is skipped over |
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| IF[0] | 0 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSIF[1] | 0 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSE | 0 -2 | |
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| ... whatever ... | | this line is skipped over |
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| ENDIF | 0 | |
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| ... whatever ... | | this line is skipped over |
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| ELSIF[1] | 1 | |
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| ... whatever ... | | this line is processed |
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| IF[0] | 1 0 | |
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| ... whatever ... | | this line is skipped over |
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| ELSIF[1] | 1 1 | |
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| ... whatever ... | | this line is processed |
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| ELSE | 1 -2 | |
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| ... whatever ... | | this line is skipped over |
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| ENDIF | 1 | |
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| ... whatever ... | | this line is processed |
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| ENDIF | | |
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Example 4:
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| IF[0] | 0 | |
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| ... whatever ... | | this line is skipped over |
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| IF[0] | 0 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSIF[0] | 0 -1 | |
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| ... whatever ... | | this line is skipped over |
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| ELSE | 0 -2 | |
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| ... whatever ... | | this line is skipped over |
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| ENDIF | 0 | |
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| ... whatever ... | | this line is skipped over |
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| ELSIF[1] | 1 | |
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| ... whatever ... | | this line is processed |
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| IF[0] | 1 0 | |
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| ... whatever ... | | this line is skipped over |
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| ELSIF[0] | 1 0 | |
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| ... whatever ... | | this line is skipped over |
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| ELSE | 1 2 | |
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| ... whatever ... | | this line is processed |
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| ENDIF | 1 | |
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| ... whatever ... | | this line is processed |
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| ENDIF | | |
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