Re: [Xen-devel] [PATCH] libxl: Fix building libxlu_cfg_y.y with bison 3.0

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Campbell writes ("Re: [Xen-devel] [PATCH] libxl: Fix building 
libxlu_cfg_y.y with bison 3.0"):
> There was a point in time where the prevailing version of bison (or
> maybe flex) in stable distro releases had a bug which meant these files
> could not be regenerated easily on common distros. I don't recall the
> details well enough to know if that time has now passed. Perhaps Ian J
> does.

We use (essential) features found only in non-ancient versions of
bison and flex.  The last time it was proposed to remove these
pregenerated files, there were complaints from people who were using
six-year-old bison and flex.

I think we should prioritise compatibility with new versions of bison
and flex, and retain the pregenerated versions of people with
incompatibly old version.

I think for 4.5 we should:

 * Regenerate the flex files with current wheezy's flex.  (I have
   reviewed the diff in the generated code.  It produces trivial
   changes which add declarations of xlu__cfg_yyget_column and
   xlu__cfg_yyset_column, but no code body changes - see below.)

 * Take the patch from Ed and regenerate the bison files too.


Konrad: can we have two freeze exceptions please ?

Risk analysis for Ed's patch:

Not taking the patch hurts systems with bison 2.7.1 or later:

  - Affected systems include Debian jessie, which will be
    released during the lifetime of 4.5.

  - Bison 2.7.1 was released in April 2013, a year and
    a half ago.  So any system which is less than 18 months out of
    date suffers pain from not updating.

Taking the patch hurts systems with old bison:

  - Bison 2.4.1 is known to work and was released in December 2008.
    So systems which suffer pain from updating are using at least
    4-year-old bison.

  - I have not investigated whether there are even older bison
    versions which are still OK with updating.

On the affected systems:

  - Attempts to build actually-from-source, or with modified
    bison input, will definitely fail.

  - Some proportion of other builds will fail anyway due to
    timestamp skew.


Risk analysis for regenerating with current wheezy's flex:

There doesn't seem to be any actual change in the generated code apart
from a few new function declarations and changes to #line directives.
So the risk of breakage is small.  Furthermore:

Not taking the patch now means that our flex file will be out of date
and may be regenerated and updated accidentally (or need to be
regenerated) at some point in the future.  That means that (a)
whatever risk of breakage we are taking might be discovered at an
inconvenient time (b) additional build system trouble might result
from an out of date file.


There isn't AFAICT a necessary connection between these two but we
normally regenerate both the bison and flex files together, if
necessary, before making any changes to the input files.

Thanks,
Ian.



diff --git a/tools/libxl/libxlu_cfg_l.c b/tools/libxl/libxlu_cfg_l.c
index df352aa..450863a 100644
--- a/tools/libxl/libxlu_cfg_l.c
+++ b/tools/libxl/libxlu_cfg_l.c
@@ -610,6 +610,10 @@ int xlu__cfg_yyget_lineno (yyscan_t yyscanner );
 
 void xlu__cfg_yyset_lineno (int line_number ,yyscan_t yyscanner );
 
+int xlu__cfg_yyget_column  (yyscan_t yyscanner );
+
+void xlu__cfg_yyset_column (int column_no ,yyscan_t yyscanner );
+
 YYSTYPE * xlu__cfg_yyget_lval (yyscan_t yyscanner );
 
 void xlu__cfg_yyset_lval (YYSTYPE * yylval_param ,yyscan_t yyscanner );
@@ -762,7 +766,7 @@ YY_DECL
 #line 53 "libxlu_cfg_l.l"
 
 
-#line 766 "libxlu_cfg_l.c"
+#line 770 "libxlu_cfg_l.c"
 
     yylval = yylval_param;
 
@@ -971,7 +975,7 @@ YY_RULE_SETUP
 #line 104 "libxlu_cfg_l.l"
 YY_FATAL_ERROR( "flex scanner jammed" );
        YY_BREAK
-#line 975 "libxlu_cfg_l.c"
+#line 979 "libxlu_cfg_l.c"
 case YY_STATE_EOF(INITIAL):
 case YY_STATE_EOF(lexerr):
        yyterminate();
diff --git a/tools/libxl/libxlu_cfg_l.h b/tools/libxl/libxlu_cfg_l.h
index 4078302..151064e 100644
--- a/tools/libxl/libxlu_cfg_l.h
+++ b/tools/libxl/libxlu_cfg_l.h
@@ -276,6 +276,10 @@ int xlu__cfg_yyget_lineno (yyscan_t yyscanner );
 
 void xlu__cfg_yyset_lineno (int line_number ,yyscan_t yyscanner );
 
+int xlu__cfg_yyget_column  (yyscan_t yyscanner );
+
+void xlu__cfg_yyset_column (int column_no ,yyscan_t yyscanner );
+
 YYSTYPE * xlu__cfg_yyget_lval (yyscan_t yyscanner );
 
 void xlu__cfg_yyset_lval (YYSTYPE * yylval_param ,yyscan_t yyscanner );
@@ -352,6 +356,6 @@ extern int xlu__cfg_yylex \
 
 #line 104 "libxlu_cfg_l.l"
 
-#line 356 "libxlu_cfg_l.h"
+#line 360 "libxlu_cfg_l.h"
 #undef xlu__cfg_yyIN_HEADER
 #endif /* xlu__cfg_yyHEADER_H */
diff --git a/tools/libxl/libxlu_disk_l.c b/tools/libxl/libxlu_disk_l.c
index 2c6e8e3..beea7f9 100644
--- a/tools/libxl/libxlu_disk_l.c
+++ b/tools/libxl/libxlu_disk_l.c
@@ -1011,6 +1011,10 @@ int xlu__disk_yyget_lineno (yyscan_t yyscanner );
 
 void xlu__disk_yyset_lineno (int line_number ,yyscan_t yyscanner );
 
+int xlu__disk_yyget_column  (yyscan_t yyscanner );
+
+void xlu__disk_yyset_column (int column_no ,yyscan_t yyscanner );
+
 /* Macros after this point can all be overridden by user definitions in
  * section 1.
  */
@@ -1155,7 +1159,7 @@ YY_DECL
 
  /*----- the scanner rules which do the parsing -----*/
 
-#line 1159 "libxlu_disk_l.c"
+#line 1163 "libxlu_disk_l.c"
 
        if ( !yyg->yy_init )
                {
@@ -1498,7 +1502,7 @@ YY_RULE_SETUP
 #line 259 "libxlu_disk_l.l"
 YY_FATAL_ERROR( "flex scanner jammed" );
        YY_BREAK
-#line 1502 "libxlu_disk_l.c"
+#line 1506 "libxlu_disk_l.c"
                        case YY_STATE_EOF(INITIAL):
                        case YY_STATE_EOF(LEXERR):
                                yyterminate();
diff --git a/tools/libxl/libxlu_disk_l.h b/tools/libxl/libxlu_disk_l.h
index 08f60e5..f615582 100644
--- a/tools/libxl/libxlu_disk_l.h
+++ b/tools/libxl/libxlu_disk_l.h
@@ -280,6 +280,10 @@ int xlu__disk_yyget_lineno (yyscan_t yyscanner );
 
 void xlu__disk_yyset_lineno (int line_number ,yyscan_t yyscanner );
 
+int xlu__disk_yyget_column  (yyscan_t yyscanner );
+
+void xlu__disk_yyset_column (int column_no ,yyscan_t yyscanner );
+
 /* Macros after this point can all be overridden by user definitions in
  * section 1.
  */
@@ -346,6 +350,6 @@ extern int xlu__disk_yylex (yyscan_t yyscanner);
 
 #line 259 "libxlu_disk_l.l"
 
-#line 350 "libxlu_disk_l.h"
+#line 354 "libxlu_disk_l.h"
 #undef xlu__disk_yyIN_HEADER
 #endif /* xlu__disk_yyHEADER_H */

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