337 lines
15 KiB
Diff
337 lines
15 KiB
Diff
From 10cd5db8821e4d313ae5245b33061e02ba8d3ff5 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Jan=20Pokorn=C3=BD?= <jpokorny@redhat.com>
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Date: Thu, 3 Aug 2017 17:40:09 +0200
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Subject: [PATCH] WIP 5: Experimental fix for libqb logging not working with
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ld.bfd 2.29
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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What's missing:
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* cross-testing programs vs. libqb prior/after this fix with ld.bfd 2.29
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* program vs. library sanity attestation for good measure
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- code header-included in the program could/shall run-time one-off
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self-test the library code actually logs anything via custom callback
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log handler
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- library could/shall attest in qb_log_init that QB_ATTR_SECTION_START
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+ STOP symbols belong to other address space than its own (dladdr?)
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* related to that, we should really enable attribute((__section__)) for
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powerpc platforms, it seems to work well there -- and related to that,
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we need to figure out how static and dynamic call sites can live
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together -- say what will happen to logging programs compiled with
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libqb w/o attribute sections when the underlying libqb is flipped
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to the one with them...
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Version 2:
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Simplify the compilation against libqb for its users that now no
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longer need to worry to use a new flag for compilation with the
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affected ld version, as semantically the same is already contained
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in libqb.so itself (it's now a linker script instead of a common
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symlink to the end versioned so file, which something known as an
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implicit linker script:
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https://sourceware.org/binutils/docs/ld/Implicit-Linker-Scripts.html).
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Version 3:
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Ditto for direct libqb.la users (incl. native examples and tests for
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which the original Makefile.am form could have been restored thanks
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to this -- not a subject of one-time configure check anymore),
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to capture the case someone is using that libtool indirection directly
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through a private checkout underneath the actual library user's repo.
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The solutions is to slightly abuse libtool's library archive handling
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and it's implicit dependency propagation within "dependency_libs"
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variable, where we inject a reference to our own artificial library
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archive that in turn eventually resolves to the discussed linker script.
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Version 4:
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Overcomes some unintended RPATH occurrences in qb-blackbox binary
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or possibly libqb.so.*. That's definitely not desired:
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https://fedoraproject.org/wiki/Packaging:Guidelines#Beware_of_Rpath
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Version 5:
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Overcomes issues when HAVE_GCC_ATTRIBUTE_SECTION is not defined, hence
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qblog_script.ld script used to carry unresolved symbolic references as
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a consequence: https://bugzilla.redhat.com/show_bug.cgi?id=1487787
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Now the script is not used at all in that case, and if accidentally was,
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there is an extra guard conditionalizing the content referring to those
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values to only the case they are expected to be defined.
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Plus some more, missing in retrospect, conditionalizing is added.
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Deficiencies of version 5 (some carried over, apparently):
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- see What's missing above
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- possibly needs and overhaul regarding documentation of the arrangement
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(now scattered throughout the files)
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Deficiencies that are not solvable as long as we use the linker script
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to participate in restoring boundary section symbols being global again:
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- /usr/bin/ld: warning: ../lib/qblog_script.ld contains output sections; did you forget -T?
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References:
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http://oss.clusterlabs.org/pipermail/developers/2017-July/000503.html
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https://bugzilla.redhat.com/show_bug.cgi?id=1477354#c8
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Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
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---
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configure.ac | 62 +++++++++++++++++++++++++++++++++++++---------
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lib/Makefile.am | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++
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lib/log.c | 7 ++++++
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lib/qblog_script.la.in | 15 +++++++++++
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lib/qblog_script.ld.in | 17 +++++++++++++
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6 files changed, 156 insertions(+), 12 deletions(-)
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create mode 100644 lib/qblog_script.la.in
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create mode 100644 lib/qblog_script.ld.in
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diff --git a/configure.ac b/configure.ac
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index fd37466..f94af71 100644
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--- a/configure.ac
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+++ b/configure.ac
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@@ -618,31 +618,68 @@ AC_SUBST(HAVE_SLOW_TESTS)
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# --- callsite sections ---
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if test "x${GCC}" = xyes; then
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+ LDFLAGS_save="${LDFLAGS}"
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AC_MSG_CHECKING([whether GCC supports __attribute__((section()) + ld supports orphan sections])
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if test "x${ac_cv_link_attribute_section}" = x ; then
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+ LDFLAGS="${LDFLAGS_save} -shared -fPIC"
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+ AC_LINK_IFELSE(
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+ [AC_LANG_SOURCE(
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+ [[#include <assert.h>
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+ extern int __start___verbose[], __stop___verbose[];
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+ int test(void) {
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+ static int my_var __attribute__((section("__verbose"))) = 3;
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+ if (__start___verbose == __stop___verbose) assert(0);
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+ return *((int *) __start___verbose);
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+ }]])],
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+ [gcc_has_attribute_section=yes; cp "conftest${EXEEXT}" "lib_conftest.so"],
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+ [gcc_has_attribute_section=no]
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+ )
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+ LDFLAGS="${LDFLAGS_save}"
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+ else
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+ gcc_has_attribute_section=${ac_cv_link_attribute_section}
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+ fi
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+ AC_MSG_RESULT($gcc_has_attribute_section)
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+
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+ # in the failing case (e.g. with ld from binutils 2.29), it's probable
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+ # linking will fail readily (hidden symbol `__stop___verbose' in
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+ # conftest is referenced by DSO), but keep the sensible test (in-binary
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+ # symbol is expected to be propagated into the library, and draw the
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+ # full circle back to binary through standard return value passing
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+ # (-rpath passed because LD_LIBRARY_PATH exporting is unwieldy here)
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+ if test "x${gcc_has_attribute_section}" = xyes; then
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+ AC_MSG_CHECKING([whether linker emits global symbols for orphan sections])
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+ LDFLAGS="${LDFLAGS_save} -L. -l_conftest -Wl,-rpath=$(pwd)"
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AC_TRY_RUN(
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AC_LANG_PROGRAM(
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[[#include <assert.h>
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- extern void * __start___verbose, * __stop___verbose;]],
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+ extern int __start___verbose[], __stop___verbose[];
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+ int test(void);]],
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[[static int my_var __attribute__((section("__verbose"))) = 5;
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if (__start___verbose == __stop___verbose) assert(0);
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- if (my_var == 5) return 0;
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- else return -1;
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+ return !(my_var == test() /*5?*/);
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]]),
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- [gcc_has_attribute_section=yes],
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- [gcc_has_attribute_section=no]
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+ [gcc_has_attribute_section_visible=yes],
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+ [gcc_has_attribute_section_visible=no]
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)
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- else
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- gcc_has_attribute_section=${ac_cv_link_attribute_section}
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- fi
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+ LDFLAGS="${LDFLAGS_save}"
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+ AC_MSG_RESULT($gcc_has_attribute_section_visible)
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+ rm -f "lib_conftest.so"
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- AC_MSG_RESULT($gcc_has_attribute_section)
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- if test $gcc_has_attribute_section = yes; then
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AC_DEFINE([QB_HAVE_ATTRIBUTE_SECTION], 1,
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[Enabling code using __attribute__((section))])
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- PACKAGE_FEATURES="$PACKAGE_FEATURES attribute-section"
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+ if test "x${gcc_has_attribute_section_visible}" = xyes; then
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+ PACKAGE_FEATURES="$PACKAGE_FEATURES attribute-section"
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+ else
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+ AC_DEFINE([QB_NEED_ATTRIBUTE_SECTION_WORKAROUND], 1,
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+ [Enabling code using __attribute__((section))])
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+ PACKAGE_FEATURES="$PACKAGE_FEATURES attribute-section-workaround"
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+ fi
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fi
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fi
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+AM_CONDITIONAL(HAVE_GCC_ATTRIBUTE_SECTION, [test "x${gcc_has_attribute_section}" = xyes])
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+AM_CONDITIONAL(NEED_GCC_ATTRIBUTE_SECTION_WORKAROUND,
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+ [test "x${gcc_has_attribute_section}" = xyes \
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+ && test "x${gcc_has_attribute_section_visible}" != xyes])
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# --- ansi ---
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if test "x${enable_ansi}" = xyes && \
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@@ -721,7 +758,8 @@ AC_CONFIG_FILES([Makefile
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docs/Makefile
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docs/common.dox
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docs/html.dox
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- docs/man.dox])
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+ docs/man.dox
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+ lib/qblog_script.la:lib/qblog_script.la.in])
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AC_OUTPUT
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diff --git a/lib/Makefile.am b/lib/Makefile.am
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index 0bebeb5..85dd434 100644
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--- a/lib/Makefile.am
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+++ b/lib/Makefile.am
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@@ -19,6 +19,7 @@
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# along with libqb. If not, see <http://www.gnu.org/licenses/>.
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+CLEANFILES = qblog_script.ld
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MAINTAINERCLEANFILES = Makefile.in
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noinst_HEADERS = ipc_int.h util_int.h ringbuffer_int.h loop_int.h \
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@@ -39,9 +40,48 @@ source_to_lint = util.c hdb.c ringbuffer.c ringbuffer_helper.c \
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log_syslog.c log_dcs.c log_format.c \
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map.c skiplist.c hashtable.c trie.c
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+# Following two files related to linkage using classic ld from binutils 2.29+
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+# with which we cannot afford to lose public access to section boundary symbols
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+# (as the mentioned version started to scope them privately by default, see
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+# the comment within the first of the files, ultimately leading to broken
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+# logging functionality of libqb) deserve a bit of explanation:
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+# * qblog_script.ld
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+# - linker script that instructs the output section that those symbols should
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+# be visible, i.e. supports the same behaviour regardless of ld version
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+# - serves two purposes:
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+# . local: libqb itself and its "private" (cf. examples) users need those
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+# symbols visible, which is achieved with a help of the other file
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+# . system-wide: whenever the non-private library users link against libqb
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+# (it's development files), this linker script with
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+# prepended INPUT command so as to refer to the actual
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+# libqb library (it's numbered alias that is eventually
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+# resolved to proper shared library) is masked as libqb.so,
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+# this arrangement achieves the libqb's user will have
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+# the discussed symbols visible alike
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+# * qblog_script.la
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+# - as mentioned earlier, this indirectly hooks into libtool machinery, with
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+# the only true intention of injecting "-Wl,<path to qblog_script.ld>"
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+# into "inherited_linker_flags" libtool archive variable, from where it's
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+# subsequently spread into the build process of all the internal library
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+# users, assuming they have their dep arranged as "user_LIBADD=libqb.la"
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+# (this also alleviates the burden on getting things right if, e.g., any
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+# libqb user consumes it directly like this from its own sub-checkout tree)
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+# - it indirectly, once libtool prechew the original link command
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+# originally referring to this file, it turns such reference into the
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+# "real" library reference (here combining libdir and old_library
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+# variables within the file), also ensures libqb itself will visibly
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+# expose the discussed symbols, because such references point again to
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+# the (not enriched) linker script file that will get interpreted just
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+# like that during the last build step of the library
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+EXTRA_libqb_la_DEPENDENCIES = qblog_script.ld qblog_script.la
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+EXTRA_DIST = qblog_script.ld.in qblog_script.la.in
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+
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libqb_la_SOURCES = $(source_to_lint) unix.c
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libqb_la_CFLAGS = $(PTHREAD_CFLAGS)
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libqb_la_LIBADD = $(LTLIBOBJS) $(dlopen_LIBS) $(PTHREAD_LIBS) $(socket_LIBS)
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+if NEED_GCC_ATTRIBUTE_SECTION_WORKAROUND
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+libqb_la_LIBADD += qblog_script.la
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+endif
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AM_LDFLAGS = $(LDFLAGS_COPY:-Bsymbolic-functions=)
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@@ -60,6 +100,33 @@ else
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endif
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endif
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+qblog_script.ld: %.ld: %.ld.in
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+ $(AM_V_GEN)$(CPP) -xc -I$(top_srcdir)/include -C -P $< \
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+ | sed -n "/$$(sed -n '/^[^#]/{s/[*\/]/\\\0/g;p;q}' $<)/{:r;p;n;br}" \
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+ > $@
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+
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+# find the libqb.so symlink's target, if so, try to find out, iteratively,
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+# its gradually shorter forms that likewise symlinks the same target as the
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+# original libqb.so path, point to that file from the linker script using
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+# qblog_script.ld as a template, storing result in place of original libqb.so
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+# (e.g., libqb.so := "INPUT(libqb.so.0) " [...] "SECTIONS { " [...] "}")
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+# NOTE: readlink nor realpath are POSIX; not chained links ready
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+# NOTE: conservative check, i.e., not per NEED_GCC_ATTRIBUTE_SECTION_WORKAROUND
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+if HAVE_GCC_ATTRIBUTE_SECTION
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+install-exec-hook: qblog_script.ld
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+ target=$$(ls -l "$(DESTDIR)$(libdir)/libqb.so" || :); \
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+ target=$${target#* -> }; t1_bn=$$(basename "$${target}" || :); \
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+ while test -n "$${t1_bn}"; do t2_bn=$${t1_bn%.*[0-9]*}; \
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+ test "$${t2_bn}" != libqb.so || break; \
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+ test -L "$${t2_bn}" || { t1_bn=$${t2_bn}; continue; }; \
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+ t2_target=$$(ls -l "$${t2_bn}" || break); t2_target=$${t2_target#* -> }; \
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+ test "$${t2_target}" = "$${target}" || break; \
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+ t1_bn=$${t2_bn}; done; test -n "$${t1_bn}" || \
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+ { echo "only applicable to SO symlink scheme"; exit 1; }; \
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+ echo "INPUT($${t1_bn})" > "$(DESTDIR)$(libdir)/libqb.so-t"
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+ cat $< >> "$(DESTDIR)$(libdir)/libqb.so-t"
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+ mv -f "$(DESTDIR)$(libdir)/libqb.so-t" "$(DESTDIR)$(libdir)/libqb.so"
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+endif
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pkgconfigdir = $(libdir)/pkgconfig
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pkgconfig_DATA = libqb.pc
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diff --git a/lib/log.c b/lib/log.c
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index bfd218f..4ed432f 100644
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--- a/lib/log.c
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+++ b/lib/log.c
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@@ -40,6 +40,13 @@
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#include "util_int.h"
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#include <regex.h>
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+#if defined(QB_NEED_ATTRIBUTE_SECTION_WORKAROUND) && !defined(S_SPLINT_S)
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+/* following only needed to force these symbols be global
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+ with ld 2.29: https://bugzilla.redhat.com/1477354 */
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+struct qb_log_callsite __attribute__((weak)) QB_ATTR_SECTION_START[] = { 0 };
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+struct qb_log_callsite __attribute__((weak)) QB_ATTR_SECTION_STOP[] = { 0 };
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+#endif
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+
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static struct qb_log_target conf[QB_LOG_TARGET_MAX];
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static uint32_t conf_active_max = 0;
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static int32_t in_logger = QB_FALSE;
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diff --git a/lib/qblog_script.la.in b/lib/qblog_script.la.in
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new file mode 100644
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index 0000000..b475835
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--- /dev/null
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+++ b/lib/qblog_script.la.in
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@@ -0,0 +1,15 @@
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+# Generated by libtool
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+# NOTE: above line is just to pass func_ltwrapper_script_p sanity check of
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+# libtool script, as we are basically sort of abusing it so as to inject
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+# our custom linker script to "private" (cf. examples) users of libqb.la
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+
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+# shall rather carry a location of old_library (possibly libdir or something
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+# else, but installed=no needed to suppress 'library moved' warning then) as
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+# it's together (with libtool implied prefix otherwise) used for linking libqb
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+libdir=@abs_builddir@
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+
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+# avoids issues with library_names (spurious rpath emitting, relink-on-install)
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+old_library=qblog_script.ld
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+
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+# subject of our injection into libqb.la impacting build time for private users
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+inherited_linker_flags=-Wl,@abs_builddir@/qblog_script.ld
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diff --git a/lib/qblog_script.ld.in b/lib/qblog_script.ld.in
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new file mode 100644
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index 0000000..1f37976
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--- /dev/null
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+++ b/lib/qblog_script.ld.in
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@@ -0,0 +1,17 @@
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+#include <qb/qblog.h>
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+/* GNU ld script
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+ This atypical arrangement enforces global visibility of boundary symbols
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+ (QB_ATTR_SECTION_START, QB_ATTR_SECTION_STOP) for the custom section
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+ QB_ATTR_SECTION used for compile-time offloading of the logging call sites
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+ tracking. While libqb relies on these being global, default linker from
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+ binutils change the visibility as of version 2.29, making the logging
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+ unusable without artificial stimulus: https://bugzilla.redhat.com/1477354 */
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+SECTIONS {
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+#ifdef QB_HAVE_ATTRIBUTE_SECTION
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+ QB_ATTR_SECTION : {
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+ QB_ATTR_SECTION_START = .;
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+ *(QB_ATTR_SECTION);
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+ QB_ATTR_SECTION_STOP = .;
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+ }
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+#endif
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+}
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--
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2.14.1
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