Support for multiple versions in versioned_symbol, compat_symbol

System Internals / glibc - Florian Weimer [] - 25 March 2021 11:33 UTC

This essentially folds compat_symbol_unique functionality into compat_symbol.

This change eliminates the need for intermediate aliases for defining multiple symbol versions, for both compat_symbol and versioned_symbol. Some binutils versions do not suport multiple versions per symbol on some targets, so aliases are automatically introduced, similar to what compat_symbol_unique did. To reduce symbol table sizes, a configure check is added to avoid these aliases if they are not needed.

The new mechanism works with data symbols as well as function symbols, due to the way an assembler-level redirect is used. It is not compatible with weak symbols for old binutils versions, which is why the definition of __malloc_initialize_hook had to be changed. This is not a loss of functionality because weak symbols do not matter to dynamic linking.

The placeholder symbol needs repeating in nptl/libpthread-compat.c now that compat_symbol is used, but that seems more obvious than introducing yet another macro.

A subtle difference was that compat_symbol_unique made the symbol global automatically. compat_symbol does not do this, so static had to be removed from the definition of __libpthread_version_placeholder.

0923f74ada Support for multiple versions in versioned_symbol, compat_symbol | 4 +++
configure | 28 +++++++++++++++ | 23 ++++++++++++
include/libc-symbols.h | 5 +--
include/shlib-compat.h | 82 ++++++++++++++++++++-----------------------
malloc/malloc.c | 2 +-
nptl/libpthread-compat.c | 16 ++++-----
sysdeps/generic/libc-symver.h | 56 +++++++++++++++++++++++++++--
sysdeps/ia64/libc-symver.h | 33 +++++++++++++++++
time/clock_getcpuclockid.c | 3 +-
time/clock_getres.c | 3 +-
time/clock_gettime.c | 3 +-
time/clock_nanosleep.c | 3 +-
time/clock_settime.c | 3 +-
14 files changed, 197 insertions(+), 67 deletions(-)


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