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Cross external-C-call ABI breadth (float/Int64 args, float returns, stack align)

Motivation

External C calls landed on all four hosted targets (i386 cdecl, aarch64 AAPCS, arm32 AAPCS32) with a deliberately narrow v1 ABI: 4/8-byte scalar/pointer arguments and an integer/pointer return only. Anything else is a hard Error('… not yet supported'). That covers the SQLite/header C-import surface (all int/pointer), but blocks any C API that passes or returns floating-point or 64-bit values — e.g. libm (sin/pow → double), sqlite3_bind_double, sqlite3_column_int64, time/size APIs returning 64-bit on 32-bit targets.

x86-64 already has the full ABI (SysV class assignment, xmm0..7, edx:eax/rax, float return bridged from xmm0); this ticket brings the three cross targets up to the same coverage and removes the v1 alignment shortcut.

Scope

Per target, for external (cdecl/AAPCS) calls only — the internal Pascal convention is unaffected:

  1. Float arguments + returns.

    • i386: floats on the stack (cdecl passes all args on the stack; a double is 8 bytes, a single 4); float return comes back in st0 → load to the value model. Today both error.
    • aarch64: AAPCS uses v0..v7 for FP args, v0 for the FP return; integer and FP arg registers are counted independently (mirror the x86-64 SysV two-class split already implemented).
    • arm32: base AAPCS (no VFP arg regs in the soft-float variant we emit) passes FP args in core registers / on the stack; a double is two words. Decide and document hard-float (VFP d0) vs soft-float once a real libm call is wired — the emitted ELF flags (EF_ARM) must match the chosen loader (armel /lib/ld-linux.so.3 vs armhf /lib/ld-linux-armhf.so.3).

  2. Int64 / UInt64 arguments + returns.

    • i386: pass as two stack words (lo then hi); return in edx:eax (the internal 64-bit model already uses this pair).
    • arm32: pass as a register/stack pair (AAPCS r0:r1 alignment rule — 64-bit args start on an even register); return in r0:r1.
    • aarch64: native 64-bit, already fine for the value but verify the external path doesn't reject it.

  3. i386 stack 16-alignment. v1 skips it (correct cdecl arg layout + caller cleanup, but esp is not 16-aligned at the call). Modern glibc/SSE callees may fault. Add the realign-around-call dance (save esp, and esp,-16, reserve the arg block, restore after) like the x86-64 external path. aarch64 (sp 16-aligned by construction) and arm32 (8-byte) need a check, not new code.

Validation

Extend test_extern_c (or a new test_extern_c_float/_int64) to call libc/libm functions exercising each case — e.g. strtod/atof (double return), pow/sin (double args+return, needs -lm → DT_NEEDED libm.so.6), atoll (Int64 return), llabs (Int64 arg+return). Run on all four targets; output must equal the x86-64 build (behavioural parity — this is a feature test, not a self-host byte gate). The aarch64/arm32 guest libm.so.6 is already in the cross sysroots provisioned by tools/install_cross_sysroot.sh.

Acceptance

External C calls accept float/single/double and Int64/UInt64 arguments and return values on i386/aarch64/arm32 with output identical to x86-64; the i386 external call site is 16-byte aligned; the v1 hard-errors are removed; make test + the three cross suites + make cross-bootstrap stay green.

Log