.\" $OpenBSD: gcc-local.1,v 1.10 2003/06/04 17:59:01 espie Exp $
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.\" Copyright (c) 2002 Marc Espie
.\"
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.Dd December 1, 2002
.Dt GCC-LOCAL 1
.Os
.Sh NAME
.Nm gcc-local
.Nd local modifications to gcc
.Sh DESCRIPTION
The
.Nm gcc
software comes with specific modifications for
.Ox .
.Bl -dash
.It
.Nm gcc
does not search under 
.Pa /usr/local
for include files nor for libraries:
as a system compiler, it only searches the system paths by default.
.It
On
.Ox ,
the 
.Fl pthread
option should be used to link threaded code, isolating the program from
operating system details.
.It
On most architectures,
trampoline code marks the smallest possible area around the trampoline stub 
executable using 
.Xr mprotect 2 ,
since the stack area is by default non-executable.
.It
The 
.Fl O2
option does not include 
.Fl fstrict-aliasing ,
as this option causes issues on some legacy code.
.Fl fstrict-aliasing
is very unsafe with code that plays tricks with casts, bypassing the 
already weak type system of C.
.It
The option
.Fl fno-builtin-<function>
was backported from 
.Nm gcc
version 3,
yielding greater control over what functions
.Nm gcc
inlines.
.It
.Nm gcc
recognizes the extra format attribute syslog, to better match
the definition of 
.Xr syslog 3 ,
and silence erroneous warnings when used with
.Fl pedantic .
.It
.Nm gcc
recognizes the extra attribute nonnull, which can be used to mark
arguments that can't be 
.Dv NULL .
On the other hand, the printf format attribute does not imply nonnull
for the format.
This allows for correct format checking on the
.Xr err 3
function family.
.It
.Nm gcc
recognizes the extra attribute sentinel, which can be used to mark varargs
function that need a
.Dv NULL
pointer to mark argument termination, like
.Xr execl 3 .
This exposes latent bugs for 64 bit architectures,
where a terminating 0 will expand to a 32 bit int, and not a full-fledged
64 bits pointer.
.It
On some
.Ox
platforms, 
.Nm gcc
still uses 
.Xr setjmp 3 /
.Xr longjmp 3 -
style exceptions, and so needs extra fixes beyond the pure 2.95.3 release.
.It
On some
platforms (mostly a.out),
.Nm gcc
uses a linker wrapper to write stubs that call global constructors and
destructors.
On
.Ox
those calls can be traced using
.Fl Wl,-trace-ctors-dtors ,
using
.Xr syslog_r 3 .
.It
On i386, the optimizer features an extra peephole which reduces the function
prologues enough to allow for the ramdisk to fit on one floppy.
.It
On
.Ox ,
.Nm gcc
comes with the
.Dq propolice
stack protection extension, which is enabled by default.
This extension reorders local variable declarations and adds stack consistency
checks at run time, in order to detect stack overflows, and will attempt to
report the problem in the system logs, and abort the faulting process.
It can be turned off using the
.Fl fno-stack-protector
commandline option.
Note that the stack protector relies on some support code in libc.
Stand-alone programs not linked against libc must either provide their own
support bits, or use the
.Fl fno-stack-protector
option.
.El
.Sh SEE ALSO
.Xr gcc 1 
.Pp
.Pa http://www.trl.ibm.com/projects/security/ssp