| Message ID | 20180831144817.31207-1-m.niestroj@grinn-global.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | Mike Snitzer |
| Headers | show |
| Series | [RESEND,v2] configure: Introduce --enable-symvers option | expand |
Dne 31.8.2018 v 16:48 Marcin Niestroj napsal(a): > Only few libc (e.g. glibc) libraries support full symbol version > resolution in runtime. There are lot of standard libraries that do not > support that, such as dietlibc, musl and uclibc. Hence there is no > reason to generate symbol versions when compiling against them. Hi Before going into depth of patch itself - I'd like to get clear first what is wrong with existing solution. #if defined(__GNUC__) was supposed to be protecting against problematic usage - but it's more towards 'gcc' compiler usage - where the version is tied to compiler infrastructure. So now you say that other libraries do not support symbol versioning at all (so I'm quite wondering how they are able to handle backward compatibility???) One would have to always introduce completely NEW symbols?? > Additionally libdevmapper.so was broken when compiled against > uclibc. Runtime linker loader caused calling dm_task_get_info_base() > function recursively, leading to segmentation fault. > > Introduce --enable-symvers[=STYLE] option, which allows to choose > between gnu and disabled symbol versioning. By default gnu symbol > versioning is used to provide backward compatibility. > __GNUC__ check is replaced now with GNU_SYMVER, which is generated by > configure script. Additionally ld version script is included only in > case of gnu option, which slightly reduces output size. Yep - the idea was to support always 'last symbol' for compilers which do not support symbol versioning. But your case seems to be you use 'gcc' compiler, but surrouding libraries are not 'versioning-aware' ? So what's you plan how to solve backward compatibility - is i.e. 'uclibc' always user in a way 'recompile everything from scratch' ?? Why is the system compiled with 'gcc' not supporting versioning? What is the plan how to resolve binary backward compatibility here? (as you clearly cannot run 'old compiled binary' with new build libdm if you provide only latest symbols in some cases) - is the 'I don't care' policy applied regularly on such system ? Zdenek -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
Hi Zdenek, Zdenek Kabelac <zkabelac@redhat.com> writes: > Dne 31.8.2018 v 16:48 Marcin Niestroj napsal(a): >> Only few libc (e.g. glibc) libraries support full symbol version >> resolution in runtime. There are lot of standard libraries that do not >> support that, such as dietlibc, musl and uclibc. Hence there is no >> reason to generate symbol versions when compiling against them. > > Hi > > Before going into depth of patch itself - I'd like to get clear first > what is wrong with existing solution. > > #if defined(__GNUC__) > > was supposed to be protecting against problematic usage - but it's > more towards 'gcc' compiler usage - where the version is tied to > compiler infrastructure. > > So now you say that other libraries do not support symbol versioning > at all (so I'm quite wondering how they are able to handle backward > compatibility???) [1] presents a general comparison of musl, uclibc, dietlibc and glibc. Please take a look at "ABI and versioning comparison" section. Some libcs do not support backward compatibility at all, which means that upgrade of libc requires upgrade of all executables. These libraries are often used in tiny embedded devices (where binary size matters), so only full system upgrade is often implemented. Regarding symbol versioning... uclibc implementation of dynamic linker ignores symbol version at all. It just searches for first occurance of a symbol, which is often the oldest symbol version. musl on the other hand is aware of symbol versioning, but I am not sure what is the logic there. For the system I compiled libdevmapper.so it turns out that the newest symbols were used by musl. [1] http://www.etalabs.net/compare_libcs.html > > One would have to always introduce completely NEW symbols?? > > >> Additionally libdevmapper.so was broken when compiled against >> uclibc. Runtime linker loader caused calling dm_task_get_info_base() >> function recursively, leading to segmentation fault. >> >> Introduce --enable-symvers[=STYLE] option, which allows to choose >> between gnu and disabled symbol versioning. By default gnu symbol >> versioning is used to provide backward compatibility. >> __GNUC__ check is replaced now with GNU_SYMVER, which is generated by >> configure script. Additionally ld version script is included only in >> case of gnu option, which slightly reduces output size. > > Yep - the idea was to support always 'last symbol' for compilers which > do not support symbol versioning. > > But your case seems to be you use 'gcc' compiler, > but surrouding libraries are not 'versioning-aware' ? My specific case, which I want to solve, is building GNU/Linux system from scratch using Buildroot [2] build system. Full image is build always from scratch, Buildroot does not support building just parts (packages/libraries) of an image. Hence my idea was to add build-time option, which Buildroot would always use (--disable-symvers) to build libdevmapper with musl and uclibc libraries. [2] https://buildroot.org/ > > So what's you plan how to solve backward compatibility - is i.e. > 'uclibc' always user in a way 'recompile everything from scratch' ?? Yes, always recompile everything (at least new library users). > > Why is the system compiled with 'gcc' not supporting versioning? That is because symbol versioning support relies on both gcc (or even binutils) and libc (runtime linker). Simple runtime linker (non aware of GNU symbol versions) just picks first symbol with exact name. This is how uclibc does that. musl on the other hand parses GNU version sections in shared libraries and chooses non `hidden` (hidden are non-default) symbols. glibc does proper symbol versioning, i.e. it checks if referenced version matches defined version. I have also checked, that bionic (Android libc) is aware of symbol versioning from around 2015. > > What is the plan how to resolve binary backward compatibility here? > (as you clearly cannot run 'old compiled binary' with new build > libdm if you provide only latest symbols in some cases) - is the 'I > don't care' policy applied regularly on such system ? Such systems should atomically replace libraries with all their users. These systems developers should explicitly request non versioned libraries, which can be achieved with introduced `--disable-symvers` option. This option is implemented similar as gcc libraries. > > > Zdenek
diff --git a/WHATS_NEW b/WHATS_NEW index 6003f0a1b..f49c1d298 100644 --- a/WHATS_NEW +++ b/WHATS_NEW @@ -1,5 +1,6 @@ Version 3.0.0 ============= + Introduce --enable-symvers[=STYLE] switch. Add 'lvm2-activation-generator:' prefix for kmsg messages logged by generator. Add After=rbdmap.service to {lvm2-activation-net,blk-availability}.service. Reduce max concurrent aios to avoid EMFILE with many devices. diff --git a/configure b/configure index d6ddbc2fa..f0ac95d13 100755 --- a/configure +++ b/configure @@ -955,6 +955,7 @@ enable_fsadm enable_blkdeactivate enable_dmeventd enable_selinux +enable_symvers enable_nls with_localedir with_confdir @@ -1670,6 +1671,9 @@ Optional Features: --disable-blkdeactivate disable blkdeactivate --enable-dmeventd enable the device-mapper event daemon --disable-selinux disable selinux support + --enable-symvers[=STYLE] + enables symbol versioning of the shared library + [default=gnu] --enable-nls enable Native Language Support Optional Packages: @@ -3067,13 +3071,11 @@ if test -z "$CFLAGS"; then : fi case "$host_os" in linux*) - CLDFLAGS="$CLDFLAGS -Wl,--version-script,.export.sym" # equivalent to -rdynamic ELDFLAGS="-Wl,--export-dynamic" # FIXME Generate list and use --dynamic-list=.dlopen.sym CLDWHOLEARCHIVE="-Wl,-whole-archive" CLDNOWHOLEARCHIVE="-Wl,-no-whole-archive" - LDDEPS="$LDDEPS .export.sym" LIB_SUFFIX=so DEVMAPPER=yes BUILD_LVMPOLLD=no @@ -3087,7 +3089,6 @@ case "$host_os" in ;; darwin*) CFLAGS="$CFLAGS -no-cpp-precomp -fno-common" - CLDFLAGS="$CLDFLAGS" ELDFLAGS= CLDWHOLEARCHIVE="-all_load" CLDNOWHOLEARCHIVE= @@ -12820,6 +12821,35 @@ done LIBS=$lvm_saved_libs fi +################################################################################ +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether to enable symbol versioning" >&5 +$as_echo_n "checking whether to enable symbol versioning... " >&6; } +# Check whether --enable-symvers was given. +if test "${enable_symvers+set}" = set; then : + enableval=$enable_symvers; + case "$enableval" in + gnu|no) ;; + *) as_fn_error $? "Unknown argument to enable/disable symvers" "$LINENO" 5 ;; + esac +else + enable_symvers=gnu +fi + +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $enable_symvers" >&5 +$as_echo "$enable_symvers" >&6; } + +if test x$GCC = xyes && test x$enable_symvers = xgnu ; then + +$as_echo "#define GNU_SYMVER 1" >>confdefs.h + + case "$host_os" in + linux*) + CLDFLAGS="$CLDFLAGS -Wl,--version-script,.export.sym" + LDDEPS="$LDDEPS .export.sym" + ;; + esac +fi + ################################################################################ { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether to enable internationalisation" >&5 $as_echo_n "checking whether to enable internationalisation... " >&6; } diff --git a/configure.ac b/configure.ac index 6d9308fec..0131664e2 100644 --- a/configure.ac +++ b/configure.ac @@ -30,13 +30,11 @@ AC_CANONICAL_TARGET([]) AS_IF([test -z "$CFLAGS"], [COPTIMISE_FLAG="-O2"]) case "$host_os" in linux*) - CLDFLAGS="$CLDFLAGS -Wl,--version-script,.export.sym" # equivalent to -rdynamic ELDFLAGS="-Wl,--export-dynamic" # FIXME Generate list and use --dynamic-list=.dlopen.sym CLDWHOLEARCHIVE="-Wl,-whole-archive" CLDNOWHOLEARCHIVE="-Wl,-no-whole-archive" - LDDEPS="$LDDEPS .export.sym" LIB_SUFFIX=so DEVMAPPER=yes BUILD_LVMPOLLD=no @@ -50,7 +48,6 @@ case "$host_os" in ;; darwin*) CFLAGS="$CFLAGS -no-cpp-precomp -fno-common" - CLDFLAGS="$CLDFLAGS" ELDFLAGS= CLDWHOLEARCHIVE="-all_load" CLDNOWHOLEARCHIVE= @@ -1359,6 +1356,31 @@ package as well (which may be called readline-devel or something similar).]) LIBS=$lvm_saved_libs fi +################################################################################ +dnl -- Symbol versioning +AC_MSG_CHECKING(whether to enable symbol versioning) +AC_ARG_ENABLE(symvers, + AC_HELP_STRING([--enable-symvers[[[=STYLE]]]], + [enables symbol versioning of the shared library [default=gnu]]), + [ + case "$enableval" in + gnu|no) ;; + *) AC_MSG_ERROR(Unknown argument to enable/disable symvers) ;; + esac], + enable_symvers=gnu) +AC_MSG_RESULT($enable_symvers) + +if test x$GCC = xyes && test x$enable_symvers = xgnu ; then + AC_DEFINE(GNU_SYMVER, 1, + [Define to use GNU versioning in the shared library.]) + case "$host_os" in + linux*) + CLDFLAGS="$CLDFLAGS -Wl,--version-script,.export.sym" + LDDEPS="$LDDEPS .export.sym" + ;; + esac +fi + ################################################################################ dnl -- Internationalisation stuff AC_MSG_CHECKING(whether to enable internationalisation) diff --git a/include/configure.h.in b/include/configure.h.in index f68b09238..15491a17b 100644 --- a/include/configure.h.in +++ b/include/configure.h.in @@ -135,6 +135,9 @@ /* Path to fsadm binary. */ #undef FSADM_PATH +/* Define to use GNU versioning in the shared library. */ +#undef GNU_SYMVER + /* Define to 1 if you have the `alarm' function. */ #undef HAVE_ALARM diff --git a/lib/misc/lib.h b/lib/misc/lib.h index f7baf9dba..0b4dfe911 100644 --- a/lib/misc/lib.h +++ b/lib/misc/lib.h @@ -41,16 +41,16 @@ * macro DM_EXPORT_SYMBOL to export the function and bind it to the * specified version string. * - * Since versioning is only available when compiling with GCC the entire - * compatibility version should be enclosed in '#if defined(__GNUC__)', - * for example: + * Since versioning is only available when compiling with GCC + * and GLIBC the entire compatibility version should be enclosed + * in '#if defined(GNU_SYMVER)', for example: * * int dm_foo(int bar) * { * return bar; * } * - * #if defined(__GNUC__) + * #if defined(GNU_SYMVER) * // Backward compatible dm_foo() version 1.02.104 * int dm_foo_v1_02_104(void); * int dm_foo_v1_02_104(void) @@ -67,7 +67,7 @@ * versions of library symbols prior to the introduction of symbol * versioning: it must never be used for new symbols. */ -#if defined(__GNUC__) +#if defined(GNU_SYMVER) #define DM_EXPORT_SYMBOL(func, ver) \ __asm__(".symver " #func "_v" #ver ", " #func "@DM_" #ver ) #define DM_EXPORT_SYMBOL_BASE(func) \ diff --git a/libdm/datastruct/bitset.c b/libdm/datastruct/bitset.c index 06bd31a9d..65ab5f184 100644 --- a/libdm/datastruct/bitset.c +++ b/libdm/datastruct/bitset.c @@ -242,7 +242,7 @@ bad: return NULL; } -#if defined(__GNUC__) +#if defined(GNU_SYMVER) /* * Maintain backward compatibility with older versions that did not * accept a 'min_num_bits' argument to dm_bitset_parse_list(). @@ -253,7 +253,4 @@ dm_bitset_t dm_bitset_parse_list_v1_02_129(const char *str, struct dm_pool *mem) return dm_bitset_parse_list(str, mem, 0); } DM_EXPORT_SYMBOL(dm_bitset_parse_list, 1_02_129); - -#else /* if defined(__GNUC__) */ - #endif diff --git a/libdm/ioctl/libdm-iface.c b/libdm/ioctl/libdm-iface.c index e775da7d9..e224cf586 100644 --- a/libdm/ioctl/libdm-iface.c +++ b/libdm/ioctl/libdm-iface.c @@ -2145,7 +2145,7 @@ void dm_lib_exit(void) _version_checked = 0; } -#if defined(__GNUC__) +#if defined(GNU_SYMVER) /* * Maintain binary backward compatibility. * Version script mechanism works with 'gcc' compatible compilers only. diff --git a/libdm/libdm-deptree.c b/libdm/libdm-deptree.c index 3e602e28b..9313af181 100644 --- a/libdm/libdm-deptree.c +++ b/libdm/libdm-deptree.c @@ -3797,7 +3797,7 @@ void dm_tree_node_set_callback(struct dm_tree_node *dnode, dnode->callback_data = data; } -#if defined(__GNUC__) +#if defined(GNU_SYMVER) /* * Backward compatible implementations. * diff --git a/libdm/libdm-stats.c b/libdm/libdm-stats.c index e9bfa9de9..691938f2c 100644 --- a/libdm/libdm-stats.c +++ b/libdm/libdm-stats.c @@ -5065,7 +5065,7 @@ int dm_stats_start_filemapd(int fd, uint64_t group_id, const char *path, * current dm_stats_create_region() version. */ -#if defined(__GNUC__) +#if defined(GNU_SYMVER) int dm_stats_create_region_v1_02_106(struct dm_stats *dms, uint64_t *region_id, uint64_t start, uint64_t len, int64_t step, int precise, const char *program_id,
Only few libc (e.g. glibc) libraries support full symbol version resolution in runtime. There are lot of standard libraries that do not support that, such as dietlibc, musl and uclibc. Hence there is no reason to generate symbol versions when compiling against them. Additionally libdevmapper.so was broken when compiled against uclibc. Runtime linker loader caused calling dm_task_get_info_base() function recursively, leading to segmentation fault. Introduce --enable-symvers[=STYLE] option, which allows to choose between gnu and disabled symbol versioning. By default gnu symbol versioning is used to provide backward compatibility. __GNUC__ check is replaced now with GNU_SYMVER, which is generated by configure script. Additionally ld version script is included only in case of gnu option, which slightly reduces output size. Providing --disable-symvers to configure script when building against uclibc library fixes segmentation fault error described above, due to lack of several versions of the same symbol in libdevmapper.so library. Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com> --- Hi, I am resending rebased (on master) patch. Changes v1 -> v2: * Set LDDEPS only when --enable-symvers=gnu WHATS_NEW | 1 + configure | 36 +++++++++++++++++++++++++++++++++--- configure.ac | 28 +++++++++++++++++++++++++--- include/configure.h.in | 3 +++ lib/misc/lib.h | 10 +++++----- libdm/datastruct/bitset.c | 5 +---- libdm/ioctl/libdm-iface.c | 2 +- libdm/libdm-deptree.c | 2 +- libdm/libdm-stats.c | 2 +- 9 files changed, 71 insertions(+), 18 deletions(-)