Subject: Gentoo gcc 4.8.3 build problem: -fstack-protector [also, Re: bug#17754]

From: behoffski <[email-masked]>
Date: Tue, 17 Jun 2014 20:16:37 +0930

G'day,

[Re: bug#17754: There is a bugfix in 4.8.3 regarding code flow analysis
that covers the reported case.  Now that Gentoo has added gcc 4.8.3 to
its package database, I've rebuilt, and the compiler now correctly
detects that the variable will always be initialised before it is used.
The unwanted behaviour in gcc 4.8.2 was part of the new "-Og" feature.]

----

New potential portability problem:  When Gentoo released their
repackaged gcc 4.8.3 (in the last 48 hours or so), they also released a
warning NEWS item regarding gcc 4.8.3 defaulting to -fstack-protector,
and gcc 4.9 onwards defaulting to -fstack-protector-strong:

         2014-06-15-gcc48_ssp
           Title                     GCC 4.8.3 defaults to -fstack-protector
           Author                    Ryan Hill <[email-masked]>
           Posted                    2014-06-15
           Revision                  1

         Beginning with GCC 4.8.3, Stack Smashing Protection (SSP) will be
         enabled by default.  The 4.8 series will enable -fstack-protector
         while 4.9 and later enable -fstack-protector-strong. [...]

         [...] these features [...] can be disabled with -fno-stack-protector.

I've just installed gcc 4.8.3, and have found that the -fstack-protector
feature results in a compilation error in lib/mbsstr.c:

         In file included from mbsstr.c:32:0:
         str-kmp.h: In function 'knuth_morris_pratt':
         str-kmp.h:35:1: error: stack protector not protecting local variables: variable length buffer [-Werror=stack-protector]
          knuth_morris_pratt (const UNIT *haystack,
          ^
         mbsstr.c: In function 'knuth_morris_pratt_multibyte':
         mbsstr.c:40:1: error: stack protector not protecting local variables: variable length buffer [-Werror=stack-protector]
          knuth_morris_pratt_multibyte (const char *haystack, const char *needle,
          ^
         cc1: all warnings being treated as errors

Re-running './configure CFLAGS="-Og -fsanitize=address -fno-stack-protector"
results in a clean build, and "make check" passes.

On a slightly-related note, Valgrind and -fsanitize=address are incompatible
(overlapping memory space usage).  Configuring with
"CFLAGS=-Og -fno-stack-protector" (no "-fsanitize=address") lets "make check"
run successfully  with Jim's Valgrind scripts referencing built images in
grep/src/.vg-tmp/.

cheers,

behoffski (Brenton Hoff)
Programmer, Grouse Software