diff --git a/test/sim/sw_testcases/pmp_u_x.c b/test/sim/sw_testcases/pmp_u_x.c
new file mode 100644
index 0000000..932a3bf
--- /dev/null
+++ b/test/sim/sw_testcases/pmp_u_x.c
@@ -0,0 +1,179 @@
+#include "tb_cxxrtl_io.h"
+#include "hazard3_csr.h"
+#include "pmp.h"
+
+// Check that PMP correctly controls U-mode X permissions, with precedence to
+// the lowest-numbered matching region. Check that partial region matches
+// cause failure no matter the permission, unless there is a lower-numbered
+// fully matching region.
+
+/*EXPECTED-OUTPUT***************************************************************
+
+Initial
+mcause = 1
+4-byte region
+mcause = 11
+Large region
+mcause = 11
+X under !X
+mcause = 11
+!X under X
+mcause = 1
+Full match under partial match, positive overhang
+mcause = 11
+Partial match under full match, positive overhang
+mcause = 1
+Full match under partial match, negative overhang
+mcause = 11
+Partial match under full match, negative overhang
+mcause = 1
+
+*******************************************************************************/
+
+static inline void enter_umode(void (*f)(void)) {
+	clear_csr(mstatus, 0x1800u);
+	write_csr(mepc, f);
+	// This function assumes that the U-mode callee will trap rather than
+	// returning via ra.
+	asm (
+		"la s0, 1f\n"
+		"csrrw s0, mtvec, s0\n"
+		"mret\n"
+		".p2align 2\n"
+		"1:\n"
+		"csrw mtvec, s0\n"
+		: : : "s0"
+	);
+}
+
+void __attribute__((aligned(4), naked)) do_ecall() {
+	asm ("ecall");
+}
+
+// A 2-byte nop followed by a 4-byte nop, so that the second nop is only
+// 2-byte-aligned. Useful for checking partial match detection.
+void __attribute__((aligned(4), naked)) do_nops() {
+	asm (
+		"c.nop\n"
+		".option push\n"
+		".option norvc\n"
+		"nop\n"
+		".option pop\n"
+		"ecall\n"
+	);
+}
+
+#define MCAUSE_INSTR_FAULT 1
+#define MCAUSE_ECALL 11
+
+int main() {
+	// Initially, there are no permissions active in the PMP, so we should get
+	// an instruction access fault at the entry point.
+	tb_puts("Initial\n");
+	enter_umode(&do_ecall);
+	tb_printf("mcause = %u\n", read_csr(mcause));
+	tb_assert(read_csr(mcause) == MCAUSE_INSTR_FAULT, "Should get instruction fault when no X permission\n");
+	tb_assert(read_csr(mepc) == (uint32_t)&do_ecall, "Bad mepc\n");
+
+	// Setting a 4-byte X region on the ecall should let us call it in U mode.
+	tb_puts("4-byte region\n");
+	write_pmpcfg(0, PMPCFG_A_NA4 << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(0, (uint32_t)&do_ecall >> 2);
+
+	enter_umode(&do_ecall);
+	tb_printf("mcause = %u\n", read_csr(mcause));
+	tb_assert(read_csr(mcause) == MCAUSE_ECALL, "Should successfully execute ecall\n");
+	tb_assert(read_csr(mepc) == (uint32_t)&do_ecall, "Bad mepc\n");
+
+	// Make the region larger (all of memory) -- should still pass.
+	tb_puts("Large region\n");
+	write_pmpcfg(0, PMPCFG_A_NAPOT << PMPCFG_A_LSB |PMPCFG_X_BITS);
+	write_pmpaddr(0, -1u);
+
+	enter_umode(&do_ecall);
+	tb_printf("mcause = %u\n", read_csr(mcause));
+	tb_assert(read_csr(mcause) == MCAUSE_ECALL, "Should successfully execute ecall\n");
+	tb_assert(read_csr(mepc) == (uint32_t)&do_ecall, "Bad mepc\n");
+
+	// Put another region on top, with no permissions -- should still pass
+	// because lower-numbered regions take precedence.
+	tb_puts("X under !X\n");
+	write_pmpcfg(0, PMPCFG_A_NAPOT << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(0, -1u);
+	write_pmpcfg(1, PMPCFG_A_NAPOT << PMPCFG_A_LSB);
+	write_pmpaddr(1, -1u);
+
+	enter_umode(&do_ecall);
+	tb_printf("mcause = %u\n", read_csr(mcause));
+	tb_assert(read_csr(mcause) == MCAUSE_ECALL, "Should successfully execute ecall\n");
+	tb_assert(read_csr(mepc) == (uint32_t)&do_ecall, "Bad mepc\n");
+
+	// Swap the two regions. Should now fail, because lower-numbered region
+	// revokes permissions of higher-numbered region.
+	tb_puts("!X under X\n");
+	write_pmpcfg(1, PMPCFG_A_NAPOT << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpcfg(0, PMPCFG_A_NAPOT << PMPCFG_A_LSB);
+
+	enter_umode(&do_ecall);
+	tb_printf("mcause = %u\n", read_csr(mcause));
+	tb_assert(read_csr(mcause) == MCAUSE_INSTR_FAULT, "Should get instruction fault when no X permission\n");
+	tb_assert(read_csr(mepc) == (uint32_t)&do_ecall, "Bad mepc\n");
+
+	// Now we'll use two regions, both with X permission, one matching all of
+	// memory and one matching the first 4 bytes of a function. The function
+	// is crafted to have a 4-byte instruction starting 2 bytes into the
+	// function, so will partially match the small region.
+
+	// First of all: small region at higher region number. Should pass,
+	// because the lower-numbered region overrides the bad match.
+	tb_puts("Full match under partial match, positive overhang\n");
+	write_pmpcfg(0, PMPCFG_A_NAPOT << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(0, -1u);
+	write_pmpcfg(1, PMPCFG_A_NA4 << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(1, (uint32_t)&do_nops >> 2);
+
+	enter_umode(&do_nops);
+	tb_printf("mcause = %u\n", read_csr(mcause));
+	tb_assert(read_csr(mcause) == MCAUSE_ECALL, "Should successfully execute ecall\n");
+	tb_assert(read_csr(mepc) == (uint32_t)&do_nops + 6, "Bad mepc\n");
+
+	// Now swap the order of the regions. The partial match of the
+	// lower-numbered region should override its permissions and the
+	// permissions of the higher-numbered region.
+	tb_puts("Partial match under full match, positive overhang\n");
+	write_pmpcfg(0, PMPCFG_A_NA4 << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(0, (uint32_t)&do_nops >> 2);
+	write_pmpcfg(1, PMPCFG_A_NAPOT << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(1, -1u);
+
+	enter_umode(&do_nops);
+	tb_printf("mcause = %u\n", read_csr(mcause));
+	tb_assert(read_csr(mcause) == MCAUSE_INSTR_FAULT, "Should get instruction fault on partial match\n");
+	tb_assert(read_csr(mepc) == (uint32_t)&do_nops + 2, "Bad mepc\n");
+
+	// Now do the same two tests, but with the partial match on the second
+	// half of the instruction rather than the first half
+	tb_puts("Full match under partial match, negative overhang\n");
+	write_pmpcfg(0, PMPCFG_A_NAPOT << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(0, -1u);
+	write_pmpcfg(1, PMPCFG_A_NA4 << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(1, ((uint32_t)&do_nops + 4) >> 2);
+
+	enter_umode(&do_nops);
+	tb_printf("mcause = %u\n", read_csr(mcause));
+	tb_assert(read_csr(mcause) == MCAUSE_ECALL, "Should successfully execute ecall\n");
+	tb_assert(read_csr(mepc) == (uint32_t)&do_nops + 6, "Bad mepc\n");
+
+	tb_puts("Partial match under full match, negative overhang\n");
+	write_pmpcfg(0, PMPCFG_A_NA4 << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(0, ((uint32_t)&do_nops + 4) >> 2);
+	write_pmpcfg(1, PMPCFG_A_NAPOT << PMPCFG_A_LSB | PMPCFG_X_BITS);
+	write_pmpaddr(1, -1u);
+
+	enter_umode(&do_nops);
+	tb_printf("mcause = %u\n", read_csr(mcause));
+	tb_assert(read_csr(mcause) == MCAUSE_INSTR_FAULT, "Should get instruction fault on partial match\n");
+	tb_assert(read_csr(mepc) == (uint32_t)&do_nops + 2, "Bad mepc\n");
+
+	return 0;
+}
diff --git a/test/sim/sw_testcases/runtests b/test/sim/sw_testcases/runtests
index 1f2b852..564cd86 100755
--- a/test/sim/sw_testcases/runtests
+++ b/test/sim/sw_testcases/runtests
@@ -13,6 +13,10 @@ if "--vcd" in args:
 
 if len(args) > 0:
 	testlist = args
+	# This happens a lot when autocomplete is used:
+	for i, n in enumerate(testlist):
+		if n.endswith(".c"):
+			testlist[i] = n[:-2]
 else:
 	testlist = []
 	for path in os.listdir():