ripple/minitrace/syscall_abi: represent prlimit64 pid with a unit struct

We don't accept nonzero values here, so we should simply reject those early.

Change-Id: I329ae76b1f44f6d3305e710ed8f5f90ee0df988f

2 files changed, 24 insertions, 12 deletions

diff --git a/ripple/minitrace/src/main.rs b/ripple/minitrace/src/main.rs
index 19be3f2..8b82b72 100644
--- a/ripple/minitrace/src/main.rs
+++ b/ripple/minitrace/src/main.rs
@@ -341,16 +341,6 @@ fn check_syscall(entry: &SyscallEntry) -> bool {
 				}
 			}
 		}
-		SyscallEntry::prlimit64 {
-			pid,
-			resource: _,
-			new_rlim: _,
-			old_rlim: _,
-		} => {
-			if pid != 0 {
-				return false;
-			}
-		}
 		SyscallEntry::getrandom {
 			ubuf: _,
 			len,
diff --git a/ripple/minitrace/src/syscall_abi/mod.rs b/ripple/minitrace/src/syscall_abi/mod.rs
index c274d0b..e050711 100644
--- a/ripple/minitrace/src/syscall_abi/mod.rs
+++ b/ripple/minitrace/src/syscall_abi/mod.rs
@@ -4,7 +4,10 @@
 
 use {
 	crate::{define_syscalls, syscall_bitflags, syscall_enums, Process},
-	std::ffi::CString,
+	std::{
+		ffi::CString,
+		fmt::{self, Debug, Write},
+	},
 };
 
 pub(crate) use arg::{ProcessSyscallArg, SyscallArg};
@@ -43,7 +46,7 @@ define_syscalls! {
 		fn openat(dfd: DirFd, filename: CString, flags: OpenFlags, mode: FileMode) -> i64 = 257;
 		fn newfstatat(dfd: DirFd, filename: CString, statbuf: *mut Stat, flags: AtFlags) -> i64 = 262;
 		fn set_robust_list(head: *mut RobustListHead, len: RobustListHeadSize) -> i64 = 273;
-		fn prlimit64(pid: i32, resource: ResourceLimit, new_rlim: *const RLimit64, old_rlim: *mut RLimit64) -> i64 = 302;
+		fn prlimit64(pid: Zero, resource: ResourceLimit, new_rlim: *const RLimit64, old_rlim: *mut RLimit64) -> i64 = 302;
 		fn getrandom(ubuf: *mut u8, len: usize, flags: GrndFlags) -> i64 = 318;
 	}
 }
@@ -126,6 +129,25 @@ syscall_enums! {
 	}
 }
 
+#[derive(Copy, Clone)]
+pub(crate) struct Zero;
+
+impl Debug for Zero {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		f.write_char('0')
+	}
+}
+
+impl SyscallArg for Zero {
+	fn try_from_reg(reg: u64) -> Option<Self> {
+		if reg == 0 {
+			Some(Zero)
+		} else {
+			None
+		}
+	}
+}
+
 #[derive(Debug, Copy, Clone)]
 pub(crate) struct SigSetSize;