The recent introduction of the optional LSE128 and RCPC3 architectural extensions to AArch64 has further led to the increased flexibility of atomic support in the architecture, with many extensions providing support for distinct atomic operations, each with different potential applications in mind.
This has led to maintenance difficulties in Libatomic, in particular regarding the way the ifunc selector is generated via a series of macro expansions at compile-time. Until now, irrespective of the atomic operation in question, all atomic functions for a particular operand size were expected to have the same number of ifunc alternatives, meaning that a one-size-fits-all approach could reasonably be taken for the selector. This meant that if, hypothetically, for a particular architecture and operand size one particular atomic operation was to have 3 different implementations associated with different extensions, libatomic would likewise be required to present three ifunc alternatives for all other atomic functions. The consequence in the design choice was the unnecessary use of function aliasing and the unwieldy code which resulted from this. This patch series attempts to remediate this issue by making the preprocessor macros defining the number of ifunc alternatives and their respective selection functions dependent on the file importing the ifunc selector-generating framework. all files are given `LAT_<FILENAME>' macros, defined at the beginning and undef'd at the end of the file. It is these macros that are subsequently used to fine-tune the behaviors of `libatomic_i.h' and `host-config.h'. In particular, the definition of the `IFUNC_NCOND(N)' and `IFUNC_COND_<n>' macros in host-config.h can now be guarded behind these new file-specific macros, which ultimately control what the `GEN_SELECTOR(X)' macro in `libatomic_i.h' expands to. As both of these headers are imported once per file implementing some atomic operation, fine-tuned control is now possible. Regtested with both `--enable-gnu-indirect-function' and `--disable-gnu-indirect-function' configurations on armv9.4-a target with LRCPC3 and LSE128 support and without. Victor Do Nascimento (4): Libatomic: Define per-file identifier macros Libatomic: Make ifunc selector behavior contingent on importing file Libatomic: Clean up AArch64 ifunc aliasing Libatomic: Clean up AArch64 `atomic_16.S' implementation file libatomic/cas_n.c | 2 + libatomic/config/linux/aarch64/atomic_16.S | 623 +++++++++---------- libatomic/config/linux/aarch64/host-config.h | 35 +- libatomic/exch_n.c | 2 + libatomic/fadd_n.c | 2 + libatomic/fand_n.c | 2 + libatomic/fence.c | 2 + libatomic/fenv.c | 2 + libatomic/fior_n.c | 2 + libatomic/flag.c | 2 + libatomic/fnand_n.c | 2 + libatomic/fop_n.c | 2 + libatomic/fsub_n.c | 2 + libatomic/fxor_n.c | 2 + libatomic/gcas.c | 2 + libatomic/gexch.c | 2 + libatomic/glfree.c | 2 + libatomic/gload.c | 2 + libatomic/gstore.c | 2 + libatomic/load_n.c | 2 + libatomic/store_n.c | 2 + libatomic/tas_n.c | 2 + 22 files changed, 357 insertions(+), 341 deletions(-) -- 2.34.1
