[musl] [PATCH] use new socket syscalls, fallback to socketcall

[Rich Felker <dalias@libc.org>]

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On Tue, Aug 04, 2020 at 03:15:06PM -0400, Rich Felker wrote:
> On Tue, Aug 04, 2020 at 08:56:42PM +0200, Markus Wichmann wrote:
> > On Tue, Aug 04, 2020 at 02:18:45PM -0400, Rich Felker wrote:
> > > Of these, only ppc, ppc64, sh, and possibly s390 (we only support
> > > 64-bit "s390x" and I'm not sure if it ever lacked the broken-down
> > > syscalls) are relevant. The rest are either unsupported by musl
> > > (including pre-EABI arm) or already using SYS_socketcall.
> > 
> > According to musl source, all currently supported architectures have
> > __NR_socket (I didn't check the other calls; I just assumed that
> > __NR_socket was a stand-in for all the other ones).
> > 
> > Therefore the required change can be performed by changing the
> > __socketcall macro (and __socketcall_cp of course). Something like this,
> > maybe? (If using GCC statement expressions is alright):
> > 
> > #ifdef __NR_socketcall
> > #define __socketcall(nm, a, b, c, d, e, f) \
> >     ({int r = __syscall(__NR_ ## nm, a, b, c, d, e, f); \
> >     if (r == -ENOSYS) \
> >         r = __syscall(__NR_socketcall, __SC_ ## nm, \
> >             (long[6]){(long)a, (long) b, (long)c, (long)d, (long)e, (long) f});
> >     r;})
> > #else
> > #define __socketcall(nm, a, b, c, d, e, f) __syscall(__NR_ ## nm, a, b, c, d, e, f)
> > #endif
> 
> This would work, but we don't use statement-expressions in musl. I
> think an alternative with an inline function would be trivial, though:
> 
> static inline long __socketcall(int sys, int sock, long a, long b, long c, long d, long e, long f)
> {
> 	long r = __syscall(sys, a, b, c, d, e, f);
> 	if (r != -ENOSYS) return r;
> 	return __syscall(SYS_socketcall, sock, ((long[6]){a, b, c, d, e, f}));
> }
> #define __socketcall(nm, a, b, c, d, e, f) __socketcall(SYS_##nm, __SC_##nm, \
> 	(long)(a), (long)(b), (long)(c), (long)(d), (long)(e), (long)(f))
> 
> However it may (will?) end up including SYS_socketcall fallback code
> even on archs that never need it if SYS_socketcall is defined.
> Probably arch/*/syscall_arch.h should #undef SYS_socketcall if it's
> never needed. I'm not sure if there are any such archs.
> 
> I kinda just thought of getting rid of the __socketcall abstraction,
> but indeed it looks like a lot of ugly boilerplate to duplicate across
> ~15 functions, so I think keeping it in src/internal/syscall.h makes
> the most sense.

OK, that roughly works. Special care is needed for SYS_accept since it
doesn't exist on i386, m68k, or s390x and needs to be emulated with
SYS_accept4. microblaze and mips (plain o32) seem to be the only archs
that define SYS_socketcall but don't ever need to use it.

Attached is a patch that seems to work implementing the above idea
with fixups. It's not heavily tested yet.

Rich

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diff --git a/arch/i386/syscall_arch.h b/arch/i386/syscall_arch.h
index 69642e57..f92b7aa9 100644
--- a/arch/i386/syscall_arch.h
+++ b/arch/i386/syscall_arch.h
@@ -87,5 +87,3 @@ static inline long __syscall6(long n, long a1, long a2, long a3, long a4, long a
 #define VDSO_CGT32_VER "LINUX_2.6"
 #define VDSO_CGT_SYM "__vdso_clock_gettime64"
 #define VDSO_CGT_VER "LINUX_2.6"
-
-#define SYSCALL_USE_SOCKETCALL
diff --git a/arch/m68k/syscall_arch.h b/arch/m68k/syscall_arch.h
index af79c306..6a9d0ae8 100644
--- a/arch/m68k/syscall_arch.h
+++ b/arch/m68k/syscall_arch.h
@@ -87,5 +87,4 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
 	return d0;
 }
 
-#define SYSCALL_USE_SOCKETCALL
 #define SYSCALL_IPC_BROKEN_MODE
diff --git a/arch/microblaze/syscall_arch.h b/arch/microblaze/syscall_arch.h
index 169013f8..61d8248e 100644
--- a/arch/microblaze/syscall_arch.h
+++ b/arch/microblaze/syscall_arch.h
@@ -95,3 +95,5 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
 }
 
 #define SYSCALL_IPC_BROKEN_MODE
+
+#undef SYS_socketcall
diff --git a/arch/mips/syscall_arch.h b/arch/mips/syscall_arch.h
index 380a94b3..5b7c38de 100644
--- a/arch/mips/syscall_arch.h
+++ b/arch/mips/syscall_arch.h
@@ -149,3 +149,5 @@ static inline long __syscall7(long n, long a, long b, long c, long d, long e, lo
 
 #define SO_SNDTIMEO_OLD 0x1005
 #define SO_RCVTIMEO_OLD 0x1006
+
+#undef SYS_socketcall
diff --git a/arch/s390x/syscall_arch.h b/arch/s390x/syscall_arch.h
index afb99852..83cc9a27 100644
--- a/arch/s390x/syscall_arch.h
+++ b/arch/s390x/syscall_arch.h
@@ -72,5 +72,3 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
 	register long r7 __asm__("r7") = f;
 	__asm_syscall("+r"(r2), "r"(r1), "r"(r3), "r"(r4), "r"(r5), "r"(r6), "r"(r7));
 }
-
-#define SYSCALL_USE_SOCKETCALL
diff --git a/src/internal/syscall.h b/src/internal/syscall.h
index 975a0031..bd073c1a 100644
--- a/src/internal/syscall.h
+++ b/src/internal/syscall.h
@@ -2,6 +2,7 @@
 #define _INTERNAL_SYSCALL_H
 
 #include <features.h>
+#include <errno.h>
 #include <sys/syscall.h>
 #include "syscall_arch.h"
 
@@ -57,15 +58,23 @@ hidden long __syscall_ret(unsigned long),
 #define __syscall_cp(...) __SYSCALL_DISP(__syscall_cp,__VA_ARGS__)
 #define syscall_cp(...) __syscall_ret(__syscall_cp(__VA_ARGS__))
 
-#ifndef SYSCALL_USE_SOCKETCALL
-#define __socketcall(nm,a,b,c,d,e,f) __syscall(SYS_##nm, a, b, c, d, e, f)
-#define __socketcall_cp(nm,a,b,c,d,e,f) __syscall_cp(SYS_##nm, a, b, c, d, e, f)
+static inline long __alt_socketcall(int sys, int sock, int cp, long a, long b, long c, long d, long e, long f)
+{
+	long r;
+	if (cp) r = __syscall_cp(sys, a, b, c, d, e, f);
+	else r = __syscall(sys, a, b, c, d, e, f);
+	if (r != -ENOSYS) return r;
+#ifndef SYS_socketcall
+	return r;
 #else
-#define __socketcall(nm,a,b,c,d,e,f) __syscall(SYS_socketcall, __SC_##nm, \
-    ((long [6]){ (long)a, (long)b, (long)c, (long)d, (long)e, (long)f }))
-#define __socketcall_cp(nm,a,b,c,d,e,f) __syscall_cp(SYS_socketcall, __SC_##nm, \
-    ((long [6]){ (long)a, (long)b, (long)c, (long)d, (long)e, (long)f }))
+	if (cp) return __syscall_cp(SYS_socketcall, sock, ((long[6]){a, b, c, d, e, f}));
+	else return __syscall(SYS_socketcall, sock, ((long[6]){a, b, c, d, e, f}));
 #endif
+}
+#define __socketcall(nm, a, b, c, d, e, f) __alt_socketcall(SYS_##nm, __SC_##nm, 0, \
+	(long)(a), (long)(b), (long)(c), (long)(d), (long)(e), (long)(f))
+#define __socketcall_cp(nm, a, b, c, d, e, f) __alt_socketcall(SYS_##nm, __SC_##nm, 1, \
+	(long)(a), (long)(b), (long)(c), (long)(d), (long)(e), (long)(f))
 
 /* fixup legacy 16-bit junk */
 
@@ -338,6 +347,10 @@ hidden long __syscall_ret(unsigned long),
 #define __SC_recvmmsg    19
 #define __SC_sendmmsg    20
 
+#ifndef SYS_accept
+#define SYS_accept SYS_accept4
+#endif
+
 #ifndef SO_RCVTIMEO_OLD
 #define SO_RCVTIMEO_OLD  20
 #endif