Package: flex
Version: 2.5.34-3
Severity: normal
I started getting new warnings from the C compile phase of
lexers as of 2.5.34, which I verified showed up in the transition
from 2.5.33-12 to 2.5.34-1. The warnings are:
warning: comparison between signed and unsigned integer expressions
I tracked it down to a change in the definition of the YY_INPUT macro.
Any gcc-4.2 or gcc-4.3 compiler will detect the problem. To reproduce,
start with a very simple example.lex:
%option nounput
%{
extern int keyword(const char *str, unsigned len);
%}
%%
[a-zA-Z_][a-zA-Z0-9$_]* { return keyword(yytext, yyleng); }
%%
Then build:
flex -o example.cc example.lex
gcc -Wall example.cc -c
The warning that pops out when using lex-2.5.34 is
example.cc: In function 'int yy_get_next_buffer()':
example.cc:934: warning: comparison between signed and unsigned integer
expressions
It's easy to see the fault in example.cc. In both flex versions,
YY_INPUT is used as
YY_INPUT( (&YY_CURRENT_BUFFER_LVALUE->yy_ch_buf[number_to_move])
(yy_n_chars), (size_t) num_to_read );
Note that the third argument is of type (size_t). The old, lint-free
definition of YY_INPUT starts
#define YY_INPUT(buf,result,max_size) \
if ( YY_CURRENT_BUFFER_LVALUE->yy_is_interactive ) \
{ \
int c = '*'; \
size_t n; \
for ( n = 0; n < max_size && \
(c = getc( yyin )) != EOF && c != '\n'; ++n ) \
buf[n] = (char) c; \
but the new definition changes the declaration of n to
int n;
which not only generates a warning for the comparison n < max_size,
it's a real mistake.
It took me some effort to isolate and analyze to this point.
I started trying to find the origin of the problem in the
flex code base, but quickly found myself in over my head.
I hope you can take it from here.
-- System Information:
Debian Release: lenny/sid
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)
Kernel: Linux 2.6.24-1-amd64 (SMP w/1 CPU core)
Locale: LANG=en_US, LC_CTYPE=en_US (charmap=ISO-8859-1)
Shell: /bin/sh linked to /bin/bash
Versions of packages flex depends on:
ii debconf [debconf-2.0] 1.5.19 Debian configuration management sy
ii libc6 2.7-8 GNU C Library: Shared libraries
ii m4 1.4.10-1 a macro processing language
Versions of packages flex recommends:
ii gcc [c-compiler] 4:4.2.2-2 The GNU C compiler
ii gcc-4.0 [c-compiler] 4.0.3-7 The GNU C compiler
ii gcc-4.2 [c-compiler] 4.2.3-1 The GNU C compiler
ii gcc-4.3 [c-compiler] 4.3-20080202-1 The GNU C compiler
-- debconf information excluded
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