[DTrace-devel] [PATCH v2 03/23] lexer: work around bug in flex <= 2.6.0

[Nick Alcock]

Flex commit f863c949, released in 2.6.1, is a one-line fix to the
generated flex skeleton that fixes an old bug that breaks yywrap();
if it returns nonzero, input() is meant to return 0 to its caller
on EOF. This bug makes it return EOF instead, which no lexer expects
(and certainly the DTrace lexer does not).

Alas we cannot get around this bug just by defining %option noyywrap,
since that still emits the same buggy piece of the skeleton but just
introduces its own yywrap() which returns 1. And there's no way to
fix the skeleton from flex itself, and we can't require flex >= 2.6.1
since OL7 has 2.5.37.

So, for now, resort to a one-line patch to the generated lexer, silently
applied and skipped if it doesn't apply.  (Any generated lexer it doesn't
apply on will have this bug fixed.)

We can remove this when we can require flex 2.6.1.

One tiny output change triggered by this: the conceptual line number on
which EOF-related errors happen is now one higher, because there's an
extra call to input() triggered by the previous fix which bumps the line
number by one (in effect, 'off EOF' is considered an extra line after
the last line in the file).  This is technically a behaviour change but
I very much doubt anyone will mind.

Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
---
 .gitignore                   |  2 ++
 dtrace.spec                  |  2 +-
 libdtrace/Build              |  3 ++-
 libdtrace/dt_lex.yywrap.diff | 11 +++++++++++
 4 files changed, 16 insertions(+), 2 deletions(-)
 create mode 100644 libdtrace/dt_lex.yywrap.diff

diff --git a/.gitignore b/.gitignore
index 18f2ecb85c6c..892c156f8910 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,8 @@
 *.[oa]
 build/
 *~
+*.rej
+*.orig
 .git-version
 
 #
diff --git a/dtrace.spec b/dtrace.spec
index 777dd28ded84..6d81222088fb 100644
--- a/dtrace.spec
+++ b/dtrace.spec
@@ -51,7 +51,7 @@
 %define glibc32 %{nil}
 %endif
 
-BuildRequires: rpm
+BuildRequires: rpm patch
 Name:         dtrace
 License:      Universal Permissive License (UPL), Version 1.0
 Group:        Development/Tools
diff --git a/libdtrace/Build b/libdtrace/Build
index 76fd32e44a2f..310a01bd453a 100644
--- a/libdtrace/Build
+++ b/libdtrace/Build
@@ -124,6 +124,7 @@ $(libdtrace-build_DIR)%.h $(libdtrace-build_DIR)%.c: $(libdtrace-build_DIR)%.y
 $(libdtrace-build_DIR)dt_lex.c: $(libdtrace-build_DIR)dt_grammar.h $(libdtrace-build_DIR)dt_lex.l
 	$(call describe-target,LEX,$(libdtrace-build_DIR)dt_lex.c)
 	flex -o$(libdtrace-build_DIR)dt_lex.c $(libdtrace-build_DIR)dt_lex.l
+	(cd $(libdtrace-build_DIR) && patch -r - -sNp0 < dt_lex.yywrap.diff >/dev/null || true)
 
 M4_DLIBS += \
 	procfs.d \
@@ -259,7 +260,7 @@ clean::
 	$(call describe-target,CLEAN,libdtrace)
 	rm -f $(libdtrace-build_DIR)dt_errtags.c
 	rm -f $(libdtrace-build_DIR)dt_grammar.h $(libdtrace-build_DIR)dt_grammar.c
-	rm -f $(libdtrace-build_DIR)dt_lex.c
+	rm -f $(libdtrace-build_DIR)dt_lex.c*
 	rm -f $(addprefix $(libdtrace-build_DIR),$(BUILD_DLIBS))
 
 install::
diff --git a/libdtrace/dt_lex.yywrap.diff b/libdtrace/dt_lex.yywrap.diff
new file mode 100644
index 000000000000..78d15a118121
--- /dev/null
+++ b/libdtrace/dt_lex.yywrap.diff
@@ -0,0 +1,11 @@
+--- dt_lex.c.orig	2023-06-13 14:00:35.440457181 +0100
++++ dt_lex.c	2023-06-13 14:00:49.910469682 +0100
+@@ -2796,7 +2796,7 @@
+ 				case EOB_ACT_END_OF_FILE:
+ 					{
+ 					if ( yywrap( ) )
+-						return EOF;
++						return 0;
+ 
+ 					if ( ! (yy_did_buffer_switch_on_eof) )
+ 						YY_NEW_FILE;
-- 
2.42.0.271.g85384428f1