Re: -fsanitize=memory

["Mike" <tankf33der@...>]

November 22, 2019 3:59 PM, "Roberto Ierusalimschy" <roberto@inf.puc-rio.br> wrote:

>> MemorySanitizer: use-of-uninitialized-value /home/mpech/lua-5.3.5/src/liolib.c:490:58 in read_line
>> 
>> Here is the line in question:
>> 
>> while (i < LUAL_BUFFERSIZE && (c = l_getc(f)) != EOF && c != '\n')
>> 
>> The tool seems to think that c is uninitialized, which is clearly
>> wrong given this line just before the loop:
>> 
>> int c = '\0';
>> 
>> What am I missing?
> 
> Might it be some problem inside macro 'l_getc' (which can be either
> getc or getc_unlocked)?
> 

0. My linux distro to play - void and arch, latest glibc 2.30, clang-llvm 9.0
(my distros and platforms park is big, I even have owl linux installed)

1.
create data file mike.txt (two lines):
abc mike
xzy

2.
create test code mike.lua (two lines):
io.input("mike.txt")
print(io.read(1, "l") -- problem here

3.
recompile lua under memory sanitizer, my CC line in Makefile:
CC= clang -g -fsanitize=memory -std=gnu99

4.
any combinations of io.read() below is OK and dont trigger fatal warning of sanitizer:
(1, 1)
(1, 128)
("l", "l") -- L and l are the same meaning here
("l", 1)
("l", "a")
(1, "a")
("a", "a")

5. so problem in io.read(1, "l") combination

6. ok

7. after read_chars() read_line() gets correct FILE stream and cursor position inside g_read()

8. sanitizer quits *immediately* in first touch of l_getc(), no while() loop occurs:
while (i < LUAL_BUFFERSIZE && (c = l_getc(f)) != EOF && c != '\n') { 

9. if i replace l_getc (getc_unlocked) to simple getc *NO* error

10. looks like false alarm caused by combination of LLVM and glibc.

(mike)