3df579626d
bin/lto-dump which may be helpful if you employ link-time optimization (LTO).
Forward port r499061 | gerald | 2019-04-15 from lang/gcc8 and gcc8-devel [1]:
GCC has two runtime libraries: The static library libgcc.a (-lgcc) and
the shared library libgcc_s.so (-lgcc_s). Both implement many of the
same functions but they also each have their unique functions. When
GCC links programs and libraries there are three possibilities:
1. gcc -static-libgcc or gcc -static: -lgcc
=> Just use libgcc.a.
2. gcc -shared-libgcc: -lgcc_s -lgcc
=> Link with libgcc_s first, so libgcc.a is only used for its unique
functions.
3. gcc: -lgcc -Wl,--as-needed -lgcc_s -Wl,--no-as-needed
=> Link with libgcc.a first so libgcc_s is only used for its unique
functions (_Unwind_* functions).
Approach 3 is the default for gcc and it's also what clang and clang++ use;
approach 2 is the default for gfortran, g++ and probably other front ends.
This patch makes 3 the default for gfortran. It significantly reduces
the use of libgcc_s. The _Unwind_* functions are also available in the
old base system libgcc_s which means this reduces the need for
-rpath /usr/local/lib/gccN in ports that depend on libraries built with
gfortran. Consider a dependency tree like this:
prog -> libA -> libgcc_s (old base system libgcc_s is fine)
-> libB -> libgcc_s (libB built with gfortran, needs new libgcc_s)
Here prog needs to be linked with -rpath /usr/local/lib/gccN even if it's
a normal C program compiled with clang. Without -rpath it will fail to
start because it loads old libgcc_s first as a dependency of libA and then
it fails to load libB. With this patch libB works with old base system
libgcc_s or may not need libgcc_s at all, so prog does not need to be
linked with -rpath.
PR: 208120 [1]
Submitted by: tijl [1]
70 lines
2.8 KiB
Text
70 lines
2.8 KiB
Text
GCC has two runtime libraries: The static library libgcc.a (-lgcc) and
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the shared library libgcc_s.so (-lgcc_s). Both implement many of the
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same functions but they also each have their unique functions. When
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gcc links programs and libraries there are three possibilities:
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1. gcc -static-libgcc or gcc -static: -lgcc
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=> Just use libgcc.a.
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2. gcc -shared-libgcc: -lgcc_s -lgcc
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=> Link with libgcc_s first, so libgcc.a is only used for its unique
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functions.
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3. gcc: -lgcc -Wl,--as-needed -lgcc_s -Wl,--no-as-needed
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=> Link with libgcc.a first so libgcc_s is only used for its unique
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functions (_Unwind_* functions).
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Approach 3 is the default for gcc and it's also what clang and clang++ use;
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approach 2 is the default for gfortran, g++ and probably other front ends.
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This patch makes 3 the default for gfortran. It significantly reduces
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the use of libgcc_s. The _Unwind_* functions are also available in the
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old base system libgcc_s which means this reduces the need for
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-rpath /usr/local/lib/gccN in ports that depend on libraries built with
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gfortran. Consider a dependency tree like this:
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prog -> libA -> libgcc_s (old base system libgcc_s is fine)
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-> libB -> libgcc_s (libB built with gfortran, needs new libgcc_s)
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Here prog needs to be linked with -rpath /usr/local/lib/gccN even if it's
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a normal C program compiled with clang. Without -rpath it will fail to
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start because it loads old libgcc_s first as a dependency of libA and then
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it fails to load libB. With this patch libB works with old base system
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libgcc_s or may not need libgcc_s at all, so prog does not need to be
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linked with -rpath.
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Upstream is unlikely accept a patch like this because libgfortran calls
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some _Unwind_* functions and so always needs libgcc_s. Also because
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every Fortran program and library links to libgfortran it makes sense
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that option 2 above is the default. On FreeBSD where clang and GCC
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compiled code can be mixed and where multiple libgcc_s may be installed,
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option 3 is just a lot easier to deal with.
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The bug that sparked this is PR 208120 (but note there's a lot of
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misleading information in that bug. CMake is not actually doing
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anything wrong.)
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--- UTC
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--- gcc/fortran/gfortranspec.c.orig 2015-06-26 17:47:23 UTC
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+++ gcc/fortran/gfortranspec.c
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@@ -404,7 +404,7 @@ For more information about these matters
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}
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}
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-#ifdef ENABLE_SHARED_LIBGCC
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+#if 0
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if (library)
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{
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unsigned int i;
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--- libgfortran/Makefile.in.orig 2019-02-22 14:22:13.000000000 +0000
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+++ libgfortran/Makefile.in 2019-02-27 16:27:08.856408000 +0000
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@@ -625,7 +625,7 @@
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$(LTLDFLAGS) $(LIBQUADLIB) ../libbacktrace/libbacktrace.la \
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$(HWCAP_LDFLAGS) \
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-lm $(extra_ldflags_libgfortran) \
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- $(version_arg) -Wc,-shared-libgcc
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+ $(version_arg)
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libgfortran_la_DEPENDENCIES = $(version_dep) libgfortran.spec $(LIBQUADLIB_DEP)
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cafexeclib_LTLIBRARIES = libcaf_single.la
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