Retro68/GCC-PATCHES.md

GCC Patches for Retro68

This (AI-generated) document describes the changes applied to GCC 16.1.0 to produce the Retro68 cross-compiler targeting classic Mac OS (m68k and PowerPC). The patch is large, but the functional changes fall into a handful of clearly-scoped areas. Build-system boilerplate updates (automake 1.15→1.16, autoconf copyright bumps, aclocal.m4 churn, Makefile.in regeneration) are noted briefly but not detailed, because they need to be re-generated rather than re-applied by hand.

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1. New target: m68k-*-macos

What it does

Adds a complete new GCC target triple m68k-*-macos for compiling classic Macintosh 68k applications using the ELF-based toolchain that the rest of Retro68 provides.

Files changed / added

File	Change
gcc/gcc/config.gcc	Adds m68k-*-macos* stanza: sets default CPU to 68020, includes m68k-none.h, m68kelf.h, m68kemb.h, and the new m68k-macos.h; adds pragma object m68k-mac-pragmas.o.
gcc/gcc/config/m68k/m68k-macos.h	New file. Defines LIBGCC_SPEC, LINK_SPEC, LIB_SPEC, CPP_SPEC (-Wno-trigraphs), and TARGET_OS_CPP_BUILTINS (defines macintosh / Macintosh).
gcc/gcc/config/m68k/t-macos	New makefile fragment. Compiles m68k-mac-pragmas.c and restricts multilib to pre-68060/cpu32/fido CPUs.
gcc/gcc/config/m68k/t-m68k	Adds multilib CPU exclusions (same as above) and includes m68k-passes.def via PASSES_EXTRA.
gcc/libgcc/config.host	Adds m68k-*-macos host entry: sets extra_parts to crtbegin.o/crtend.o and includes the float-lib makefile fragment.

Re-applying to a newer GCC

Search config.gcc for the existing m68k-*-elf* block and add an analogous m68k-*-macos* block immediately before or after it. The new header file m68k-macos.h and makefile fragments (t-macos, changes to t-m68k) can be copied verbatim. The libgcc/config.host entry mirrors the m68k-*-elf* entry – copy and adapt it.

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2. New target: powerpc-apple-macos

What it does

Adds a GCC target for compiling PowerPC Mac OS (pre-X) applications using AIX/XCOFF object format.

Files changed / added

File	Change
gcc/gcc/config.gcc	Adds powerpc-apple-macos* stanza: includes rs6000/xcoff.h, rs6000/macos.h; uses collect2, AIX thread model, rs6000/t-macos makefile.
gcc/gcc/config/rs6000/macos.h	New file (~320 lines). Sets DEFAULT_ABI ABI_AIX, configures XCOFF, defines TARGET_OS_CPP_BUILTINS (defines macintosh, Macintosh, __ppc__, __POWERPC__, __NATURAL_ALIGNMENT__), sets LINK_SPEC, LIB_SPEC, LIBGCC_SPEC (with -carbon multilib variant), integer type sizes, DWARF section names, and EH data format.
gcc/gcc/config/rs6000/t-macos	New (mostly-comment) makefile fragment.
gcc/gcc/config/rs6000/rs6000.opt	Adds the -carbon driver option used in LIBGCC_SPEC.
gcc/gcc/config/rs6000/rs6000.cc	Adds the pascal function attribute to the RS/6000 attribute table. Also fixes a crash in rs6000_xcoff_declare_object_name by guarding symtab_node::get_create with a null check.
gcc/libgcc/config.host	Adds powerpc-*-macos entry using t-fdpbit and rs6000/t-ibm-ldouble.
gcc/libgcc/config/rs6000/cxa_finalize.c	Fixes a compilation error: changes return type of catomic_compare_and_exchange_bool_acq from boolean_t to int.

Re-applying to a newer GCC

• Add the powerpc-apple-macos* block to config.gcc modelled on the AIX block.
• Copy macos.h and t-macos into gcc/config/rs6000/.
• Add the -carbon option to rs6000.opt.
• In rs6000.cc, add the pascal entry to rs6000_attribute_table[] and apply the null-check fix in rs6000_xcoff_declare_object_name.
• Fix cxa_finalize.c (boolean_t → int).

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3. pascal calling convention support (m68k)

What it does

Implements the classic Mac OS Pascal calling convention for 68k targets:

• Arguments are pushed left-to-right (caller pushes first argument first).
• The callee cleans the stack on return (using rtd on 68020+, or a manual sequence on earlier chips).
• The return value of non-void Pascal functions is written into a slot that the caller pre-allocates on the stack before the arguments (the slot is placed before the first argument; the callee stores the result there before returning).
• Pascal function names are uppercased in the assembler output (standard Mac OS convention) via m68k_mangle_decl_assembler_name.
• Declared with __attribute__((pascal)) or via the pascal macro defined in TARGET_OS_CPP_BUILTINS as __attribute__((__pascal__)).

Files changed

File	Change
gcc/gcc/config/m68k/m68k.h	Adds IS_PASCAL_FUNC macro hooking into the generic call machinery. Extends CUMULATIVE_ARGS from a plain int to a struct (bytes, index, total_count, regparam, arg_regs[]). Changes INIT_CUMULATIVE_ARGS to call the new m68k_init_cumulative_args. Adds pascal to TARGET_OS_CPP_BUILTINS. Adds M68K_SYMBOLIC_CALL_BSRW_C enum value. Marks a6/a5 as fixed registers (index 13/14 in FIXED_REGISTERS and CALL_USED_REGISTERS). Changes d2 to call-used.
gcc/gcc/config/m68k/m68k.cc	Implements m68k_init_cumulative_args, m68k_is_pascal_func, m68k_return_pops_args (returns size for pascal functions), m68k_mangle_decl_assembler_name (uppercases names of pascal functions), m68k_function_arg_padding (always PAD_UPWARD). Disables TARGET_PROMOTE_PROTOTYPES (commented out).
gcc/gcc/calls.cc	initialize_argument_information: adds reverse_args parameter; when true, iterates arguments in forward order instead of reverse, so pascal functions have arguments pushed left-to-right. expand_call: calls IS_PASCAL_FUNC, pre-allocates return-value slot on stack, disables tail-call optimisation, reads return value back from stack after the call.
gcc/gcc/function.cc	assign_parms_augmented_arg_list: reverses fnargs array for pascal functions so that the first declared parameter is processed last (matching left-to-right push order). expand_function_end: writes the return value to the pre-allocated stack slot for pascal functions.
gcc/gcc/config/m68k/m68k.md	Adds call_pop / call_value_pop expanders and corresponding *call_pop / *symbolic_call_value_pop_jsr / *symbolic_call_value_pop_bsr insns that emit jsr/bsr with a combined stack-pointer adjustment (for callee-pops-args). Updates the return pattern to emit rtd #N (68020+) or a manual load/jump sequence (for older chips) when crtl->args.pops_args is set.

Re-applying to a newer GCC

• The changes to m68k.h (CUMULATIVE_ARGS struct, IS_PASCAL_FUNC, INIT_CUMULATIVE_ARGS, TARGET_OS_CPP_BUILTINS, register masks) must be re-applied; check for nearby context lines because other parts of m68k.h may have shifted.
• In m68k.cc, add the new functions (m68k_init_cumulative_args, m68k_is_pascal_func, m68k_mangle_decl_assembler_name, m68k_function_arg_padding) and the pascal/regparam/raw_inline entries in m68k_attribute_table.
• The calls.cc changes are architecture-independent; look for the initialize_argument_information signature and expand_call body. The reverse_args parameter must be threaded through the call.
• The function.cc argument reversal and return-value store are also architecture-independent; guard them with #ifdef IS_PASCAL_FUNC.
• The new insn patterns in m68k.md (call_pop, call_value_pop and their internal * variants) can be inserted after the existing call patterns.

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4. regparam calling convention (register-parameter passing)

What it does

Implements __attribute__((regparam("D0,A0,..."))) to pass function arguments in specified registers, matching the Mac OS #pragma parameter convention. This is required to call Toolbox traps that receive parameters in specific registers.

Files changed

File	Change
gcc/gcc/config/m68k/m68k.h	CUMULATIVE_ARGS struct carries regparam flag, arg_regs[], and index.
gcc/gcc/config/m68k/m68k.cc	m68k_init_cumulative_args parses the regparam attribute string or looks up a pragma_parameter_directives table. m68k_function_arg returns the register RTX when cum->regparam is set. m68k_function_value returns the register specified by arg_regs[0] when regparam is active.
gcc/gcc/config/m68k/m68k-mac-pragmas.c	New file. Implements #pragma parameter FuncName [returnreg] (arg1reg, arg2reg, …) parsing. Populates pragma_parameter_directives (a std::map<string, vector<int>>). Registers the pragma via REGISTER_TARGET_PRAGMAS.
gcc/gcc/config/m68k/m68k.h	REGISTER_TARGET_PRAGMAS() calls m68k_register_pragmas() (declared extern).

Re-applying to a newer GCC

The m68k-mac-pragmas.c file can be copied verbatim. The hooks into m68k.h/m68k.cc depend on the CUMULATIVE_ARGS struct already having been extended (patch 3 above). The c_target_objs/cxx_target_objs lines in config.gcc must include m68k-mac-pragmas.o for all m68k targets (or at least for the m68k-*-macos variant).

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5. raw_inline attribute (inline Toolbox trap opcodes)

What it does

Allows a function to be defined as a sequence of 16-bit machine-code words that are emitted literally when the function is called, rather than generating a real call instruction. This is how Mac OS Toolbox traps are declared: e.g. pascal void ExitToShell(void) = 0xA9F4;.

Files changed

File	Change
gcc/gcc/config/m68k/m68k.cc	output_call: checks for raw_inline attribute on the callee; if found, emits .short 0xNNNN, … words directly into the assembler output instead of a jsr/bsr. m68k_ok_for_sibcall_p: returns false for raw_inline functions (cannot tail-call). m68k_rawinline_p: predicate testing whether a SYMBOL_REF refers to a raw_inline function.
gcc/gcc/config/m68k/predicates.md	Adds rawinline_operand predicate; adds it to const_call_operand so that calls to raw_inline symbols are accepted as valid call operands.
gcc/gcc/c/c-parser.cc	c_parser_declaration_or_fndef: when a FUNCTION_DECL is assigned an initialiser, calls c_parser_inline_opcodes instead of the normal initialiser path. c_parser_inline_opcodes: parses a brace-or-comma list of integer constants and attaches them as a __raw_inline__ attribute.
gcc/gcc/cp/parser.cc	Same logic added to cp_parser_init_declarator (C++ parser).
gcc/gcc/c/c-decl.cc	Suppresses "function is initialized like a variable" error for this pattern.
gcc/gcc/calls.cc	prepare_call_address: skips the normal funexp preparation for calls to raw_inline functions (no force_reg, no mode conversion).

Re-applying to a newer GCC

The parser changes in c-parser.cc and cp/parser.cc are the trickiest to re-apply because the surrounding code evolves across GCC versions. The key insertion point in c-parser.cc is inside c_parser_declaration_or_fndef, where an initialiser is parsed for a function declarator – look for the start_init call. In cp/parser.cc look for cp_parser_pure_specifier. The output_call changes in m68k.cc are self-contained and easy to re-apply.

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6. Pascal string literals ("\p...")

What it does

Adds a "\p" string prefix that produces a Pascal-style length-prefixed string: the first byte contains the string length, followed by the characters. Both the C and C++ parsers are patched identically.

Files changed

File	Change
gcc/gcc/c-family/c-common.h	Adds CTI_UCHAR_ARRAY_TYPE enum value and uchar_array_type_node macro.
gcc/gcc/c-family/c-common.cc	Allocates uchar_array_type_node (array of unsigned char) in c_common_nodes_and_builtins; adds the corresponding TREE_TYPE case in fix_string_type.
gcc/gcc/c-family/c-lex.cc	In lex_string: detects "\p prefix, temporarily replaces \p with \n (a known-good escape) to let the normal string parser run, then overwrites byte 0 with the real string length. Sets TREE_TYPE to uchar_array_type_node for Pascal strings.
gcc/gcc/c/c-parser.cc	Same Pascal-string detection applied to c_parser_string_literal.
gcc/gcc/cp/parser.cc	Same Pascal-string detection applied to cp_parser_string_literal.

Re-applying to a newer GCC

The c-common.h/c-common.cc additions are straightforward – add the new array type adjacent to char_array_type_node. In c-lex.cc, c-parser.cc, and cp/parser.cc look for the string-literal parsing loop and the CPP_STRING TREE_TYPE assignment; insert the \p-detection block immediately before the call to cpp_interpret_string.

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7. MacsBug symbol output

What it does

After each function's final rts/rtd instruction, emits a MacsBug-format symbol record: a length byte (or two-byte length for names ≥ 32 chars) followed by the function name ASCII bytes and a word-aligned padding short. This allows the MacsBug debugger to display symbolic function names. When -ffunction-sections is active the symbol is placed in a per-function .macsbug section.

A global counter retro68_hack_asm_rts_counter tracks whether the last emitted instruction was an rts/rtd; if not, an extra rts is prepended.

The ASM_DECLARE_FUNCTION_SIZE macro in m68k.h hooks into the normal ELF function-size emission point and calls m68k_write_macsbug_name.

Files changed

File	Change
gcc/gcc/config/m68k/m68k.cc	Adds m68k_write_macsbug_name (writes the MacsBug record to the assembler file).
gcc/gcc/config/m68k/m68k.h	Defines ASM_DECLARE_FUNCTION_SIZE to call m68k_write_macsbug_name.
gcc/gcc/final.cc	Defines and decrements retro68_hack_asm_rts_counter in output_asm_insn. Sets the counter to 2 in the return pattern output.
gcc/gcc/config/m68k/m68k.md	Sets retro68_hack_asm_rts_counter = 2 before emitting the rts/rtd instruction.
gcc/gcc/config/m68k/m68k-protos.h	Declares m68k_write_macsbug_name.
gcc/bfd/elflink.c (binutils)	Keeps .macsbug sections from being GC'd (see BINUTILS-PATCHES.md).

Re-applying to a newer GCC

• In final.cc, declare retro68_hack_asm_rts_counter as a global int and decrement it inside output_asm_insn.
• In m68k.md, find the return define_insn and set the counter before the rts/rtd output.
• Copy m68k_write_macsbug_name to m68k.cc and its prototype to m68k-protos.h.
• Add ASM_DECLARE_FUNCTION_SIZE to m68k.h (or the target-specific header m68k-macos.h).

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8. Computed-goto section placement (m68k_unique_section)

What it does

Overrides TARGET_ASM_UNIQUE_SECTION to detect arrays of label pointers (computed-goto jump tables) and place them in a named .text.funcname.varname section, keeping them in the text segment where position-independent code can reach them.

Files changed

File	Change
gcc/gcc/config/m68k/m68k.cc	Adds m68k_unique_section function; hooks it via TARGET_ASM_UNIQUE_SECTION.

Re-applying to a newer GCC

Copy the function and #undef/#define hook verbatim into m68k.cc.

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9. PC-relative bsr.w call mode

What it does

Adds a fifth M68K_SYMBOLIC_CALL variant M68K_SYMBOLIC_CALL_BSRW_C that emits bsr.w %c0 (word-displacement branch-to-subroutine with a 16-bit offset). This is activated automatically when -msep-data is in effect (i.e. when TARGET_PCREL is set), replacing the default bsr.l.

Files changed

File	Change
gcc/gcc/config/m68k/m68k.h	Adds M68K_SYMBOLIC_CALL_BSRW_C to the enum.
gcc/gcc/config/m68k/m68k.cc	Sets m68k_symbolic_call_var to BSRW_C when TARGET_PCREL; adds the "bsr%.w %c0" string constant to the switch. Updates all `m68k_symbolic_call_var == BSR_C
gcc/gcc/config/m68k/m68k.md	Adds BSRW_C to the guards of the BSR call patterns.

Re-applying to a newer GCC

Add the enum value and string constant, update the three-way || guards in the condition and in m68k_option_override.

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10. Register-save fix for PIC register in sep-data mode

What it does

When -msep-data is active (TARGET_SEP_DATA), the PIC register is used for a different purpose than standard -fPIC; suppresses the unconditional save/restore of the PIC register that m68k_save_reg would otherwise force.

Files changed

File	Change
gcc/gcc/config/m68k/m68k.cc	In m68k_save_reg, conditions the PIC-register save on !TARGET_SEP_DATA.

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11. combine-stack-adj pass cloneable

What it does

Makes pass_stack_adjustments cloneable (adds a clone() method) so that it can be inserted multiple times in the pass pipeline. This is needed because the m68k-passes.def file inserts an additional CSA pass early (after pass_combine) to eliminate redundant stack moves when calling pascal functions.

Files changed

File	Change
gcc/gcc/combine-stack-adj.cc	Adds virtual opt_pass *clone() to pass_stack_adjustments.
gcc/gcc/config/m68k/m68k-passes.def	New file. Inserts pass_stack_adjustments after pass_combine (instance 1).
gcc/gcc/config/m68k/t-m68k	Adds PASSES_EXTRA += $(srcdir)/config/m68k/m68k-passes.def.

Re-applying to a newer GCC

Check whether pass_stack_adjustments still lacks a clone() method. If so, add it. Copy m68k-passes.def verbatim. Add PASSES_EXTRA to t-m68k.

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12. RTL analysis / reload fixes for PUSH_ROUNDING

What it does

Two fixes that work around m68k's unusual byte-push behaviour (the 68000 stack pointer always decrements by at least 2 bytes even for a byte push):

1. expr.cc (find_args_size_adjust): wraps GET_MODE_SIZE with PUSH_ROUNDING(...) for PRE_INC/POST_INC/PRE_DEC/POST_DEC addressing modes, and guards the whole block with #ifdef PUSH_ROUNDING. Without this, GCC miscomputes stack-frame sizes when byte values are pushed.

2. reload1.cc (elimination_effects): marks a frame-pointer elimination as impossible when the access uses POST_DEC/POST_INC addressing (prevents incorrect frame-pointer elimination through push/pop sequences).

3. rtlanal.cc (set_noop_p): extends the memory-to-memory noop detection to recognise (mem (post_inc r)) → (mem (pre_dec r)) as a noop (a push followed by a pop of the same register with PUSH_ROUNDING).

4. combine.cc: comments out a gcc_assert in distribute_notes that fires incorrectly when ACCUMULATE_OUTGOING_ARGS is false (which is the case for m68k).

Re-applying to a newer GCC

These are relatively surgical changes. In each file, search for the surrounding function name. The combine.cc assert may have been removed or moved upstream; verify before applying.

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13. m68k_function_value signature change

What it does

Changes m68k_function_value to accept an outgoing boolean parameter (matching the TARGET_FUNCTION_VALUE hook signature) and to look up regparam register assignments for functions with that attribute. Adds the TARGET_FUNCTION_VALUE target hook definition, replacing the old FUNCTION_VALUE macro. Always returns D0 for ordinary functions (the #if 0 block of pointer-in-A0 logic is disabled but preserved for reference).

Files changed

File	Change
gcc/gcc/config/m68k/m68k.cc	Extends m68k_function_value signature; updates m68k_ok_for_sibcall_p to call it directly.
gcc/gcc/config/m68k/m68k.h	Comments out the FUNCTION_VALUE macro; adds TARGET_FUNCTION_VALUE hook.
gcc/gcc/config/m68k/m68k-protos.h	Updates prototype.
gcc/gcc/config/m68k/m68kemb.h	Removes the FUNCTION_VALUE override (no longer needed since the hook supersedes the macro).

Re-applying to a newer GCC

Check whether the TARGET_FUNCTION_VALUE hook signature still matches; GCC may have changed it. Remove the FUNCTION_VALUE macro from both m68k.h and m68kemb.h.

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14. libcpp character constant warning suppression

What it does

Suppresses a "multi-character character constant" warning for 4-character constants (i.e. 'abcd'-style OSType/FourCC literals that are pervasive in Mac OS code).

Files changed

File	Change
gcc/libcpp/charset.cc	In narrow_str_to_charconst, adds && i != 4 to the warn_multichar condition.

Re-applying to a newer GCC

A one-line change; find the warn_multichar condition and add the i != 4 guard.

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15. libgcc compiled with -ffunction-sections

What it does

Adds -ffunction-sections to LIBGCC2_CFLAGS so that each libgcc helper function lands in its own ELF section. This allows the linker to dead-strip unused runtime helpers, which is important for small Mac applications.

Files changed

File	Change
gcc/libgcc/Makefile.in	Appends -ffunction-sections to LIBGCC2_CFLAGS.

Re-applying to a newer GCC

Locate LIBGCC2_CFLAGS in libgcc/Makefile.in and append -ffunction-sections.

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16. AArch64 Darwin host hooks

What it does

Adds a minimal host hook file for AArch64 macOS build hosts (Apple Silicon). This allows GCC to be built on Apple Silicon machines; the file simply includes the standard Darwin host hook header.

Files changed

File	Change
gcc/gcc/config/aarch64/host-aarch64-darwin.c	New file.
gcc/gcc/config.host	Adds aarch64-*-darwin* case pointing to the new file and aarch64/x-darwin.

Re-applying to a newer GCC

Check whether upstream GCC already added AArch64 Darwin host support; if not, copy the file and the config.host entry.

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17. Build system / tooling updates

These changes update generated or infrastructure files and must be re-generated rather than applied literally when porting to a new GCC base:

• gcc/compile, gcc/depcomp, gcc/missing: script version bumps (2012 → 2018 era) and MSYS support additions.
• gcc/libbacktrace/aclocal.m4, gcc/libcc1/aclocal.m4, gcc/libstdc++-v3/aclocal.m4, gcc/libstdc++-v3/Makefile.in: automake 1.15.1 → 1.16.3 regeneration.
• gcc/libcpp/configure, gcc/libcpp/configure.ac: adds setlocale to AC_CHECK_FUNCS; fixes a putc_unlocked declaration check typo.
• gcc/gcc/system.h: reorders C++ standard-library includes so that <string> comes before safe-ctype.h; moves the INCLUDE_STRING guard to the correct location. Fixes a Cygwin build issue with fputs_unlocked.
• gcc/libcc1/libcc1plugin.cc, gcc/libcc1/libcp1plugin.cc: use #define INCLUDE_VECTOR instead of #include <vector> directly.
• gcc/zlib/zutil.h: removes dead fdopen workaround for old Metrowerks toolchain under MACOS/TARGET_OS_MAC.
• gcc/newlib/libc/machine/powerpc/setjmp.S: (not shown in excerpts above, likely a minor fix for PowerPC setjmp).

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Summary of patches to re-apply when upgrading GCC

Priority	Area	Complexity
Essential	New target m68k-*-macos (config.gcc, m68k-macos.h, t-macos)	Low – mostly new files
Essential	New target powerpc-apple-macos (config.gcc, macos.h, rs6000.cc, rs6000.opt)	Medium
Essential	Pascal calling convention (m68k.h, m68k.cc, calls.cc, function.cc, m68k.md)	High
Essential	regparam attribute + #pragma parameter (m68k.cc, m68k-mac-pragmas.c)	Medium
Essential	raw_inline attribute (c-parser.cc, cp/parser.cc, c-decl.cc, m68k.cc, predicates.md)	Medium
Essential	Pascal string literals (c-common.*, c-lex.cc, c-parser.cc, cp/parser.cc)	Low
Important	MacsBug symbol output (m68k.cc, m68k.h, final.cc, m68k.md)	Medium
Important	PUSH_ROUNDING fixes (expr.cc, reload1.cc, rtlanal.cc, combine.cc)	Low
Important	-ffunction-sections for libgcc	Low
Quality	4-char constant warning (libcpp/charset.cc)	Trivial
Quality	PC-relative bsr.w mode	Low
Quality	CSA pass cloneable + extra pass	Low
Build only	AArch64 Darwin host hooks	Low
Build only	Build system regeneration	Re-generate, not re-apply