Hello folks,
this recent Fedora change:
https://fedoraproject.org/wiki/Changes/Add_FORTIFY_SOURCE%3D3_to_distribution_build_flags
Made me think:
Which compiler flags we need to store in Python and which can we omit?
In order to make Python extension modules binary compatible with Python, Python
saves the compiler flags at compile-time and reuses them when building
extension modules.
Historically, we had troubles with this approach because some of the flags are
unusable without redhat-rpm-config, annobin etc.
As a result, there are now 2 compiler flags macros available for RPM:
%{build_cflags} and %{extension_cflags} (same for ldflags etc.).
While Python itself is built with %{build_cflags}, it saves %{extension_cflags}
in sysconfig.
The flags differ like this:
$ diff -u <(rpm --eval '%build_cflags' | tr ' ' '\n') <(rpm --eval
'%extension_cflags' | tr ' ' '\n') | grep ^-
--flto=auto
--ffat-lto-objects
--specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
--specs=/usr/lib/rpm/redhat/redhat-annobin-cc1
$ diff -u <(rpm --eval '%build_ldflags' | tr ' ' '\n') <(rpm --eval
'%extension_ldflags' | tr ' ' '\n') | grep ^-
--specs=/usr/lib/rpm/redhat/redhat-hardened-ld
--specs=/usr/lib/rpm/redhat/redhat-annobin-cc1
(There are also some other differences wrt
https://fedoraproject.org/wiki/Changes/Package_information_on_ELF_objects but
those are apparently harder to get from outside of a real build.)
The current set of flags from Python can be obtained by:
>>> sysconfig.get_config_var('CFLAGS')
'-Wsign-compare -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DNDEBUG -O2 -fexceptions -g
-grecord-gcc-switches -pipe -Wall -Werror=format-security -U_FORTIFY_SOURCE
-Wp,-U_FORTIFY_SOURCE -Wp,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS
-fstack-protector-strong -m64 -mtune=generic -fasynchronous-unwind-tables
-fstack-clash-protection -fcf-protection -D_GNU_SOURCE -fPIC -fwrapv -O2
-fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security
-U_FORTIFY_SOURCE -Wp,-U_FORTIFY_SOURCE -Wp,-D_FORTIFY_SOURCE=3
-Wp,-D_GLIBCXX_ASSERTIONS -fstack-protector-strong -m64 -mtune=generic
-fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection
-D_GNU_SOURCE -fPIC -fwrapv -O2 -fexceptions -g -grecord-gcc-switches -pipe
-Wall -Werror=format-security -U_FORTIFY_SOURCE -Wp,-U_FORTIFY_SOURCE
-Wp,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -fstack-protector-strong
-m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection
-fcf-protection -D_GNU_SOURCE -fPIC -fwrapv'
>>> sysconfig.get_config_var('LDFLAGS')
'-Wl,-z,relro -Wl,--as-needed -Wl,-z,now -Wl,--build-id=sha1 -g
-Wl,-z,relro -Wl,--as-needed -Wl,-z,now -Wl,--build-id=sha1 -g'
I wonder if other flags should be removed as well.
Isn't Python built e.g. with -Werror=format-security or -Wsign-compare binary
compatible with extension modules built without it?
What about FORTIFY_SOURCE and others?
Is there a compiler flags expert here who could help me determine what flags
could (or even should) be removed from %{extension_*flags}?
Thanks,
--
Miro Hrončok
--
Phone: +420777974800
IRC: mhroncok
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