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Subject: |
Gentoo gcc 4.8.3 build problem: -fstack-protector [also, Re: bug#17754] |
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Date: |
Tue, 17 Jun 2014 20:16:37 +0930 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 |
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.]
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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 <address@hidden>
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
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--- Begin Message ---
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Subject: |
Re: bug#17793: Gentoo gcc 4.8.3 build problem: -fstack-protector [also, Re: bug#17754] |
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Date: |
Tue, 17 Jun 2014 12:28:54 -0700 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 |
behoffski wrote:
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,
^
These warnings don't indicate any bugs in the code; they're merely about
incomplete run-time checking in the underlying implementation. I was
particularly amused by a refusal to compile a function on the grounds
that its code doesn't use the stack!
So let's just disable the warnings. I pushed the attached patch.
Valgrind and -fsanitize=address are incompatible
Thanks, I didn't know that. Too bad, but understandable. Neither tool
dominates the other, so I guess we'll have to use them separately.
0001-build-avoid-Wstack-protector.patch
Description: Text document
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