On Thu, Jun 30, 2016 at 12:08 AM, Eric Botcazou <ebotca...@adacore.com> wrote: > Hi, > > this patch implements generic support for the elimination of stack trampolines > and, consequently, of the need to make the stack executable when pointers to > nested functions are used. That's done on a per-language and per-target basis > (i.e. there is 1 language hook and 1 target hook to parameterize it) and there > are no changes whatsoever in code generation if both are not turned on (and > the patch implements a -ftrampolines option to let the user override them). > > The idea is based on the fact that, for targets using function descriptors as > per their ABI like IA-64, AIX or VMS platforms, stack trampolines "degenerate" > into descriptors built at run time on the stack and thus made up of data only, > which in turn means that the stack doesn't need to be made executable.
As you are not able to handle all trampolines that way I always wondered if we can allocate space for the trampolines statically for those cases we can compute do not happen in a recursive path (or avoid them if we do not need a static chain anyway, not sure if we optimize for this case currently). Richard. > This descriptor-based scheme is implemented generically for nested functions, > i.e. the nested function lowering pass builds generic descriptors instead of > trampolines on the stack when encountering pointers to nested functions, which > means that there are 2 kinds of pointers to functions and therefore a run-time > identification mechanism is needed for indirect calls to distinguish them. > > Because of that, enabling the support breaks binary compatibility (for code > manipulating pointers to nested functions). That's OK for Ada and nested > functions are first-class citizens in the language anyway so we really need > this, but not for C so for example Ada doesn't use it at the interface with C > (when objects have "convention C" in Ada parlance). > > This was bootstrapped/regtested on x86_64-suse-linux but AdaCore has been > using it on native platforms (Linux, Windows, Solaris, etc) for years. > > OK for the mainline? > > > 2016-06-29 Eric Botcazou <ebotca...@adacore.com> > > PR ada/37139 > PR ada/67205 > * common.opt (-ftrampolines): New option. > * doc/invoke.texi (Code Gen Options): Document it. > * doc/tm.texi.in (Trampolines): Add TARGET_CUSTOM_FUNCTION_DESCRIPTORS > * doc/tm.texi: Regenerate. > * builtins.def: Add init_descriptor and adjust_descriptor. > * builtins.c (expand_builtin_init_trampoline): Do not issue a warning > on platforms with descriptors. > (expand_builtin_init_descriptor): New function. > (expand_builtin_adjust_descriptor): Likewise. > (expand_builtin) <BUILT_IN_INIT_DESCRIPTOR>: New case. > <BUILT_IN_ADJUST_DESCRIPTOR>: Likewise. > * calls.c (prepare_call_address): Remove SIBCALLP parameter and add > FLAGS parameter. Deal with indirect calls by descriptor and adjust. > Set STATIC_CHAIN_REG_P on the static chain register, if any. > (call_expr_flags): Set ECF_BY_DESCRIPTOR for calls by descriptor. > (expand_call): Likewise. Move around call to prepare_call_address > and pass all flags to it. > * cfgexpand.c (expand_call_stmt): Reinstate CALL_EXPR_BY_DESCRIPTOR. > * gimple.h (enum gf_mask): New GF_CALL_BY_DESCRIPTOR value. > (gimple_call_set_by_descriptor): New setter. > (gimple_call_by_descriptor_p): New getter. > * gimple.c (gimple_build_call_from_tree): Set CALL_EXPR_BY_DESCRIPTOR. > (gimple_call_flags): Deal with GF_CALL_BY_DESCRIPTOR. > * langhooks.h (struct lang_hooks): Add custom_function_descriptors. > * langhooks-def.h (LANG_HOOKS_CUSTOM_FUNCTION_DESCRIPTORS): Define. > (LANG_HOOKS_INITIALIZER): Add LANG_HOOKS_CUSTOM_FUNCTION_DESCRIPTORS. > * rtl.h (STATIC_CHAIN_REG_P): New macro. > * rtlanal.c (find_first_parameter_load): Skip static chain registers. > * target.def (custom_function_descriptors): New POD hook. > * tree.h (FUNC_ADDR_BY_DESCRIPTOR): New flag on ADDR_EXPR. > (CALL_EXPR_BY_DESCRIPTOR): New flag on CALL_EXPR. > * tree-core.h (ECF_BY_DESCRIPTOR): New mask. > Document FUNC_ADDR_BY_DESCRIPTOR and CALL_EXPR_BY_DESCRIPTOR. > * tree.c (make_node_stat) <tcc_declaration>: Set function alignment to > DEFAULT_FUNCTION_ALIGNMENT instead of FUNCTION_BOUNDARY. > (build_common_builtin_nodes): Initialize init_descriptor and > adjust_descriptor. > * tree-nested.c: Include target.h. > (struct nesting_info): Add 'any_descr_created' field. > (get_descriptor_type): New function. > (lookup_element_for_decl): New function extracted from... > (create_field_for_decl): Likewise. > (lookup_tramp_for_decl): ...here. Adjust. > (lookup_descr_for_decl): New function. > (convert_tramp_reference_op): Deal with descriptors. > (build_init_call_stmt): New function extracted from... > (finalize_nesting_tree_1): ...here. Adjust and deal with descriptors. > * defaults.h (DEFAULT_FUNCTION_ALIGNMENT): Define. > (TRAMPOLINE_ALIGNMENT): Set to above instead of FUNCTION_BOUNDARY. > * config/aarch64/aarch64.h (TARGET_CUSTOM_FUNCTION_DESCRIPTORS):Define > * config/alpha/alpha.h (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Likewise. > * config/arm/arm.h (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Likewise. > * config/arm/arm.c (arm_function_ok_for_sibcall): Return false for an > indirect call by descriptor if all the argument registers are used. > * config/i386/i386.h (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Define. > * config/ia64/ia64.h (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Likewise. > * config/mips/mips.h (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Likewise. > * config/pa/pa.h (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Likewise. > * config/rs6000/rs6000.h (TARGET_CUSTOM_FUNCTION_DESCRIPTORS):Likewise > * config/sparc/sparc.h (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Likewise. > ada/ > * gcc-interface/misc.c (LANG_HOOKS_CUSTOM_FUNCTION_DESCRIPTORS):Define > * gcc-interface/trans.c (Attribute_to_gnu) <Attr_Access>: Deal with > a zero TARGET_CUSTOM_FUNCTION_DESCRIPTORSspecially for 'Code_Address. > Otherwise, if TARGET_CUSTOM_FUNCTION_DESCRIPTORS is positive, set > FUNC_ADDR_BY_DESCRIPTOR for 'Access/'Unrestricted_Access of nested > subprograms if the type can use an internal representation. > (call_to_gnu): Likewise, but set CALL_EXPR_BY_DESCRIPTOR on indirect > calls if the type can use an internal representation. > > > 2016-06-29 Eric Botcazou <ebotca...@adacore.com> > > * gnat.dg/trampoline3.adb: New test. > * gnat.dg/trampoline4.adb: Likewise. > > -- > Eric Botcazou
