[PATCH] libgo: use _off_t for mmap offset argument

[soeren@soeren-tempel.net]

From: Sören Tempel <soeren@soeren-tempel.net>

On glibc-based systems, off_t is a 32-bit type on 32-bit systems and a
64-bit type on 64-bit systems by default. However, on systems using musl
libc off_t is unconditionally a 64-bit type. As such, it is insufficient
to use a uintptr type for the mmap offset parameter.

Presently, the (incorrect) mmap declaration causes a libgo run-time
failure on 32-bit musl systems (fatal error: runtime: cannot allocate
memory). This commit fixes this run-time error.

Signed-off-by: Sören Tempel <soeren@soeren-tempel.net>
---
This implements what has been proposed by Ian in a GitHub comment
https://github.com/golang/go/issues/51280#issuecomment-1046322011

I don't have access to a 32-bit glibc system to test this on but
this does seem to work fine on 32-bit and 64-bit musl systems.

 libgo/go/runtime/mem_gccgo.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libgo/go/runtime/mem_gccgo.go b/libgo/go/runtime/mem_gccgo.go
index fa3389d8..07bf325a 100644
--- a/libgo/go/runtime/mem_gccgo.go
+++ b/libgo/go/runtime/mem_gccgo.go
@@ -15,7 +15,7 @@ import (
 //go:linkname sysFree
 
 //extern mmap
-func sysMmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uintptr) unsafe.Pointer
+func sysMmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off _off_t) unsafe.Pointer
 
 //extern munmap
 func munmap(addr unsafe.Pointer, length uintptr) int32
@@ -38,7 +38,7 @@ func init() {
 }
 
 func mmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uintptr) (unsafe.Pointer, int) {
-	p := sysMmap(addr, n, prot, flags, fd, off)
+	p := sysMmap(addr, n, prot, flags, fd, _off_t(off))
 	if uintptr(p) == _MAP_FAILED {
 		return nil, errno()
 	}