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lib/utils/printf: Fix printf on release builds

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When using newer glibc's the compiler automatically sets
_FORTIFY_SOURCE when building with -O1 and this causes
a special inlined version of printf to be declared which
then bypasses our version of printf.
This commit is contained in:
Dave Hylands 2016-01-26 09:46:40 -08:00 committed by Paul Sokolovsky
parent 7b05b1b225
commit 6a804cbaba
1 changed files with 25 additions and 0 deletions
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unix/Makefile
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@ -28,6 +28,31 @@ CFLAGS += -g
COPT = -O0
else
COPT = -Os #-DNDEBUG
# _FORTIFY_SOURCE is a feature in gcc/glibc which is intended to provide extra
# security for detecting buffer overflows. Some distros (Ubuntu at the very least)
# have it enabled by default.
#
# gcc already optimizes some printf calls to call puts and/or putchar. When
# _FORTIFY_SOURCE is enabled and compiling with -O1 or greater, then some
# printf calls will also be optimized to call __printf_chk (in glibc). Any
# printfs which get redirected to __printf_chk are then no longer synchronized
# with printfs that go through mp_printf.
#
# In MicroPython, we don't want to use the runtime library's printf but rather
# go through mp_printf, so that stdout is properly tied into streams, etc.
# This means that we either need to turn off _FORTIFY_SOURCE or provide our
# own implementation of __printf_chk. We've chosen to turn off _FORTIFY_SOURCE.
# It should also be noted that the use of printf in MicroPython is typically
# quite limited anyways (primarily for debug and some error reporting, etc
# in the unix version).
#
# Information about _FORTIFY_SOURCE seems to be rather scarce. The best I could
# find was this: https://securityblog.redhat.com/2014/03/26/fortify-and-you/
# Original patchset was introduced by
# https://gcc.gnu.org/ml/gcc-patches/2004-09/msg02055.html .
#
# Turning off _FORTIFY_SOURCE is only required when compiling with -O1 or greater
CFLAGS += -U _FORTIFY_SOURCE
endif
# On OSX, 'gcc' is a symlink to clang unless a real gcc is installed.