shithub: rgbds

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Fix undefined behavior in yyunputstr
Refer to comment at lexer.c:100 for more info

--- a/src/asm/lexer.c

+++ b/src/asm/lexer.c

@@ -97,10 +97,16 @@

 	len = strlen(s);

-	pLexBuffer -= len;

-

-	if (pLexBuffer < pLexBufferRealStart)

+	/*

+	 * It would be undefined behavior to subtract `len` from pLexBuffer and

+	 * potentially have it point outside of pLexBufferRealStart's buffer,

+	 * this is why the check is done this way.

+	 * Refer to https://github.com/rednex/rgbds/pull/411#discussion_r319779797

+	 */

+	if (pLexBuffer - pLexBufferRealStart < len)

 		fatalerror("Buffer safety margin exceeded");

+

+	pLexBuffer -= len;

 	memcpy(pLexBuffer, s, len);

 }