glcpp: Don't use alternation in the lookahead for empty pragmas.

We've found that there's a buffer overrun bug in flex that's triggered by
using alternation in a lookahead pattern.

Fortunately, we don't need to match the exact {NEWLINE} expression to
detect an empty pragma. It suffices to verify that there are no non-space
characters before any newline character. So we can use a simple [\r\n] to
get the desired behavior while avoiding the flex bug.

Fixes the regression of piglit's 17000-consecutive-chars-identifier test,
(which has been crashing since commit
04e40fd337a244ee77ef9553985e9398ff0344af ).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=82472
Signed-off-by: Carl Worth <[email protected]>
Reviewed-by: Kenneth Graunke <[email protected]>

CC: <[email protected]>

1 files changed, 8 insertions, 2 deletions

diff --git a/src/glsl/glcpp/glcpp-lex.l b/src/glsl/glcpp/glcpp-lex.l
index 98d500ec0be..fa9aa506912 100644
--- a/src/glsl/glcpp/glcpp-lex.l
+++ b/src/glsl/glcpp/glcpp-lex.l
@@ -289,8 +289,14 @@ HEXADECIMAL_INTEGER	0[xX][0-9a-fA-F]+[uU]?
 }
 
 	/* Swallow empty #pragma directives, (to avoid confusing the
-	 * downstream compiler). */
-<HASH>pragma{HSPACE}*/{NEWLINE} {
+	 * downstream compiler).
+	 *
+	 * Note: We use a simple regular expression for the lookahead
+	 * here. Specifically, we cannot use the complete {NEWLINE} expression
+	 * since it uses alternation and we've found that there's a flex bug
+	 * where using alternation in the lookahead portion of a pattern
+	 * triggers a buffer overrun. */
+<HASH>pragma{HSPACE}*/[\r\n] {
 	BEGIN INITIAL;
 }