flex scanner push-back overflow about bpftrace

[Delta-in-hub]

The problem seems to be with the statement #include <linux/watch_queue.h>

[ajor]

Minimised repro:

#include <linux/watch_queue.h>

BEGIN
{
  IOC_WATCH_QUEUE_SET_FILTER;
}

I assume it's a problem with our dodgy macro parsing code:

bpftrace/src/lexer.l

Lines 251 to 287 in ce8f81a

	{ident} {
	static int unput_count = 0;
	if (driver.bpftrace_.macros_.count(yytext) != 0)
	{
	const char *s = driver.bpftrace_.macros_[yytext].c_str();
	int z;
	// NOTE(mmarchini) workaround for simple recursive
	// macros. More complex recursive macros (for
	// example, with operators) will go into an
	// infinite loop. Yes, we should fix that in the
	// future.
	if (strcmp(s, yytext) == 0)
	{
	unput_count = 0;
	return Parser::make_IDENT(yytext, loc);
	}
	else
	{
	int leng = YY_BUF_SIZE;
	std::string original_s(s);
	std::string original_yytext(yytext);
	for (z=strlen(s) - 1; z >= 0; z--){
	if (unput_count >= 1000 || leng <= 0) {
	driver.error(loc, std::string("Macro recursion limit reached: ")
	+ original_yytext + ", " + original_s);
	yyterminate();
	}
	unput(s[z]);
	unput_count++;
	leng--;
	}
	}
	} else {
	unput_count = 0;
	return Parser::make_IDENT(yytext, loc);
	}
	}