syscall_emul: adding link system call

Change-Id: If8922c2233bbe1f6fce35f64d1a44b91d2cfeed2
Reviewed-on: https://gem5-review.googlesource.com/11489
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Brandon Potter <Brandon.Potter@amd.com>

src/arch/x86/linux/process.cc

@@ -306,7 +306,7 @@ static SyscallDesc syscallDescs64[] = {
     /*  83 */ SyscallDesc("mkdir", unimplementedFunc),
     /*  84 */ SyscallDesc("rmdir", unimplementedFunc),
     /*  85 */ SyscallDesc("creat", unimplementedFunc),
-    /*  86 */ SyscallDesc("link", unimplementedFunc),
+    /*  86 */ SyscallDesc("link", linkFunc),
     /*  87 */ SyscallDesc("unlink", unlinkFunc),
     /*  88 */ SyscallDesc("symlink", unimplementedFunc),
     /*  89 */ SyscallDesc("readlink", readlinkFunc),

src/sim/syscall_emul.cc

@@ -519,6 +519,25 @@ unlinkHelper(SyscallDesc *desc, int num, Process *p, ThreadContext *tc,
     return (result == -1) ? -errno : result;
 }
 
+SyscallReturn
+linkFunc(SyscallDesc *desc, int num, Process *p, ThreadContext *tc)
+{
+    string path;
+    string new_path;
+
+    int index = 0;
+    auto &virt_mem = tc->getMemProxy();
+    if (!virt_mem.tryReadString(path, p->getSyscallArg(tc, index)))
+        return -EFAULT;
+    if (!virt_mem.tryReadString(new_path, p->getSyscallArg(tc, index)))
+        return -EFAULT;
+
+    path = p->fullPath(path);
+    new_path = p->fullPath(new_path);
+
+    int result = link(path.c_str(), new_path.c_str());
+    return (result == -1) ? -errno : result;
+}
 
 SyscallReturn
 mkdirFunc(SyscallDesc *desc, int num, Process *p, ThreadContext *tc)

src/sim/syscall_emul.hh

@@ -203,6 +203,10 @@ SyscallReturn unlinkHelper(SyscallDesc *desc, int num,
 SyscallReturn unlinkFunc(SyscallDesc *desc, int num,
                          Process *p, ThreadContext *tc);
 
+/// Target link() handler
+SyscallReturn linkFunc(SyscallDesc *desc, int num, Process *p,
+                       ThreadContext *tc);
+
 /// Target mkdir() handler.
 SyscallReturn mkdirFunc(SyscallDesc *desc, int num,
                         Process *p, ThreadContext *tc);