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Date: Tue, 13 Feb 2018 15:49:55 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] Possible patch for __syscall_cp
* Nicholas Wilson <nicholas.wilson@...lvnc.com> [2018-02-13 14:28:32 +0000]:
>
> In __syscall_cp.c, there's a call to __syscall which deliberately *disables* macro expansion, forcing the call to go via the __syscall function. On Wasm, I don't currently provide this function, instead I'm using the macros for __syscall to redirect via the __syscall<N> functions.
>
> This call in __syscall_cp looks to be practically the only place in the whole of Musl where macro expansion is prevented for __syscall (other than in src/internal/syscall.h itself, and arch/mips/syscall_arch.h). So on those grounds it's a bit suspicious, given that every other caller of __syscall uses the macros from internal/syscall.h.
>
> If there is a rationale, I could just define __syscall() in arch/wasm/syscall_arch.h - but I'd rather not if it's not meant to be called. Would it be possible instead to apply the patch below, and allow macro expansion?
>
> I can't see a risk, although I don't understand the cancellation-point implementation very well. There's no recursion possible, since plain __syscall() never redirects to any of the __syscall_cp machinery, so expansion oughtn't to cause problems on any archs?
>
i think your patch is ok (__syscall6 should behave the same
way as __syscall other than the inlining), but you can fix
it for your target only by adding
static inline long __syscall(long n, long a, long b, long c, long d, long e, long f)
{
return __syscall6(n,a,b,c,d,e,f);
}
to syscall_arch.h
> diff --git a/src/thread/__syscall_cp.c b/src/thread/__syscall_cp.c
> index 09a2be84..7b870faa 100644
> --- a/src/thread/__syscall_cp.c
> +++ b/src/thread/__syscall_cp.c
> @@ -8,7 +8,7 @@ static long sccp(syscall_arg_t nr,
> syscall_arg_t u, syscall_arg_t v, syscall_arg_t w,
> syscall_arg_t x, syscall_arg_t y, syscall_arg_t z)
> {
> - return (__syscall)(nr, u, v, w, x, y, z);
> + return __syscall(nr, u, v, w, x, y, z);
> }
>
> weak_alias(sccp, __syscall_cp_c);
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