purego: Support 32 arguments on 64bit

[tmc]

What issue is this addressing?

Closes #425

What type of issue is this addressing?

feature

What this PR does | solves

This increases the # of supported arguments to 32.

[Copilot]

Pull request overview

This PR expands PureGo’s supported argument count for 64-bit targets to 32 (aligning with existing 32-bit limits) by widening the syscall argument container, updating per-arch syscall assembly to spill additional stack arguments, and adding ABI tests to exercise higher-arity calls.

Changes:

• Increase SyscallN max supported arguments to 32 on supported 64-bit Unix-like targets (Windows remains capped at 15).
• Extend per-architecture syscall assembly stubs to pass a16–a32 (and adjust stack frame sizing accordingly).
• Add new ABI test functions/tests for 20/32 uintptr args and a 32-arg mixed int/float case.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
syscall.go	Raises maxArgs to 32 for selected 64-bit targets and routes non-Windows calls through runtime_cgocall using a pooled args struct.
syscall_32bit.go	Changes 32-bit SyscallN to use pooled args + runtime_cgocall.
syscall_64bit_fallback.go	Adds a fallback implementation (still maxArgs=15) for 64-bit Unix-like targets outside the explicitly supported arch list.
syscall_sysv.go	Adjusts callback argument decoding to account for ppc64le stack slot progression with float register args.
sys_amd64.s	Expands stack spill area and spills a16–a32 for amd64 SysV.
sys_arm64.s	Expands stack spill area and spills a16–a32 for arm64.
sys_loong64.s	Expands stack spill area and spills a16–a32 for loong64.
sys_riscv64.s	Expands stack spill area and spills a16–a32 for riscv64.
sys_s390x.s	Expands stack spill area and spills a16–a32 for s390x.
sys_ppc64le.s	Expands stack spill area and now loads additional float regs + spills a16–a32 for ppc64le.
func.go	Updates RegisterFunc marshaling/validation to use cached float-reg counts and adds a ppc64le-specific stack index adjustment.
testdata/abitest/abi_test.c	Adds C helpers to validate 20/32-argument passing and a 32-arg mixed int/float case.
func_test.go	Adds/updates ABI tests for 20/32 argument cases and improves panic assertions.

Comments suppressed due to low confidence (1)

sys_amd64.s:45

• In syscall15X on amd64 the args pointer is stored and later loaded via PTR_ADDRESS(BP), but the stack frame is created by subtracting STACK_SIZE from SP while leaving BP pointing above the allocated frame. This causes the pointer to be written outside the allocated STACK_SIZE region into the caller’s stack frame, corrupting the caller’s stack and potentially enabling crashes or code execution if an attacker can trigger calls through this path. Ensure the args pointer is saved within the allocated frame (e.g., based off SP or a negative offset from BP) so all accesses stay inside the STACK_SIZE region.

#define STACK_SIZE 224
#define PTR_ADDRESS (STACK_SIZE - 8)

// syscall15X calls a function in libc on behalf of the syscall package.
// syscall15X takes a pointer to a struct like:
// struct {
//	fn    uintptr
//	a1    uintptr
//	a2    uintptr
//	a3    uintptr
//	a4    uintptr
//	a5    uintptr
//	a6    uintptr
//	a7    uintptr
//	a8    uintptr
//	a9    uintptr
//	a10    uintptr
//	a11    uintptr
//	a12    uintptr
//	a13    uintptr
//	a14    uintptr
//	a15    uintptr
//	r1    uintptr
//	r2    uintptr
//	err   uintptr
// }
// syscall15X must be called on the g0 stack with the
// C calling convention (use libcCall).
GLOBL ·syscall15XABI0(SB), NOPTR|RODATA, $8
DATA ·syscall15XABI0(SB)/8, $syscall15X(SB)
TEXT syscall15X(SB), NOSPLIT|NOFRAME, $0
	PUSHQ BP
	MOVQ  SP, BP
	SUBQ  $STACK_SIZE, SP
	MOVQ  DI, PTR_ADDRESS(BP) // save the pointer

---

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[tmc]

Addressing copilot's comment.

[hajimehoshi]

This PR requires rebasing

[tmc]

This PR requires rebasing

rebased.

[hajimehoshi]

IIUC, this file is for an OS and an architecture PureGo does not support. Is this correct?

[hajimehoshi]

This is not answered yet

[hajimehoshi]

I'm not sure why you have not answered this...

[hajimehoshi]

I know this file no longer exists and instead you put syscall_64bit.go, but could you explain the purposes of the files?

[tmc]

sorry missed this comment -- it was originally basically unused but compilable code. since then the syscalln was put into -> syscall_64bit.go and syscall_32bit.go but i'm guessing you want to keep the 64bit code in syscall.go, which i'll do now.

[hajimehoshi]

The test is failing now

[hajimehoshi]

I'm waiting for an answer at #431 (comment)

[tmc]

IIUC, this file is for an OS and an architecture PureGo does not support. Is this correct?

Missed that, addressing now and will resolve that conflict.

[tmc]

Moved syscall_64bit.go to (back to) syscall.go and rebase to main.

[hajimehoshi]

#431 (comment)

[tmc]

#431 (comment)

responded above

[tmc]

opened #444

[hajimehoshi]

You might need to rebase or merge the main branch.

[tmc]

rebased to upstream/main

[TotallyGamerJet]

LGTM! @hajimehoshi