On 11/10/2016 03:30 AM, Jan Kurik wrote:
= Proposed System Wide Change: Fedora 26 C/C++ Compilation Flags Updates =
https://fedoraproject.org/wiki/Changes/Fedora26CFlags
Change owner(s):
* Florian Weimer <fweimer AT redhat DOT com>
This change updates the default C/C++ compilation flags, as determined
by the redhat-rpm-config package.
== Detailed Description ==
This change covers the following modifications to the default C and
C++ compiler flags in the redhat-rpm-config package.
snip
* Add -Werror=implicit-function-declaration: Implicit function
declarations allows a programmer to call functions without declaring
them (or including the relevant header files). The official C language
specification has not supported implicit function declarations for
almost two decades now. GCC still supports them as a GNU extension.
Implicit function declarations introduce bugs because these functions
use a different calling convention and have a fixed return type of
int. Resulting issues are pointer truncation (on 64-bit
architectures), exposure of padding bits (particular for
bool-returning functions on x86_64), and unexpected lack of hardening.
Implicit function declarations are not part of C++ (with or without
GNU extensions), and adjusting C code accordingly simplifies reuse in
C++ projects.
* Add -Werror=implicit-int: Implicit ints were removed from the C
programming language at the same time as implicit function
definitions, and were also retained as a GNU extension. Implicit ints
are usually source code bugs, and the presence of such code may
interfere with future C language directions (for example, consider how
C++ reused the auto keyword and an omitted type specifier).
The main risk from these changes are incorrect autoconf feature
checks, which often rely on technically invalid C fragments. However,
a review of existing configure scripts did not find any places where
they relied on these two problematic GNU extensions.
I've run into a reasonable number of failures of (custom) configure
checks due to this. Mainly calling exit() without including stdlib.h.
So keep alert everyone. Unfortunately this can lead to unpredictable
and perhaps hard to detect changes.
--
Orion Poplawski
Technical Manager 303-415-9701 x222
NWRA/CoRA Division FAX: 303-415-9702
3380 Mitchell Lane or...@cora.nwra.com
Boulder, CO 80301 http://www.cora.nwra.com
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