[PATCH v4 5/5] arm64: vdso32: Implement __vdso_futex_robust_try_unlock()

["André Almeida" <andrealmeid@igalia.com>]

Based on aarch64 implementation, provide a 32 bit entry point for
this vDSO.

In order to keep compatibility with arm64_futex_robust_unlock_get_pop(),
make sure to store the pop address at r2 and the compare result value
at r3.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 arch/arm64/kernel/vdso.c            |  9 +++++++++
 arch/arm64/kernel/vdso32/Makefile   |  4 ++++
 arch/arm64/kernel/vdso32/vdso.lds.S |  9 +++++++++
 arch/arm64/kernel/vdso32/vfutex.c   | 33 +++++++++++++++++++++++++++++++++
 4 files changed, 55 insertions(+)

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 283b38684ef7..e72a9f086999 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -71,6 +71,15 @@ static void vdso_futex_robust_unlock_update_ips(enum vdso_abi abi, struct mm_str
 
 		futex_set_vdso_cs_range(fd, 0, success, end, false);
 	}
+
+#ifdef CONFIG_COMPAT_VDSO
+	if (abi == VDSO_ABI_AA32) {
+		success = (uintptr_t) VDSO_SYMBOL(vdso, futex_list32_try_unlock_cs_success);
+		end = (uintptr_t) VDSO_SYMBOL(vdso, futex_list32_try_unlock_cs_end);
+
+		futex_set_vdso_cs_range(fd, 1, success, end, true);
+	}
+#endif
 }
 #else
 static inline void vdso_futex_robust_unlock_update_ips(enum vdso_abi abi, struct mm_struct *mm) { }
diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
index 4bd60f059f4a..f3190125c68b 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -97,6 +97,10 @@ munge := ../../../arm/vdso/vdsomunge
 hostprogs := $(munge)
 
 c-obj-vdso := note.o
+ifdef CONFIG_FUTEX_ROBUST_UNLOCK
+  c-obj-vdso += vfutex.o
+endif
+
 c-obj-vdso-gettimeofday := vgettimeofday.o
 
 ifneq ($(c-gettimeofday-y),)
diff --git a/arch/arm64/kernel/vdso32/vdso.lds.S b/arch/arm64/kernel/vdso32/vdso.lds.S
index c374fb0146f3..46c0123b2684 100644
--- a/arch/arm64/kernel/vdso32/vdso.lds.S
+++ b/arch/arm64/kernel/vdso32/vdso.lds.S
@@ -87,6 +87,15 @@ VERSION
 		__vdso_clock_getres;
 		__vdso_clock_gettime64;
 		__vdso_clock_getres_time64;
+#ifdef CONFIG_FUTEX_ROBUST_UNLOCK
+		__vdso_futex_robust_list32_try_unlock;
+#endif
 	local: *;
 	};
 }
+
+#ifdef CONFIG_FUTEX_ROBUST_UNLOCK
+VDSO_futex_list32_try_unlock_cs_success = __futex_list32_try_unlock_cs_success;
+VDSO_futex_list32_try_unlock_cs_start = __futex_list32_try_unlock_cs_start;
+VDSO_futex_list32_try_unlock_cs_end = __futex_list32_try_unlock_cs_end;
+#endif
diff --git a/arch/arm64/kernel/vdso32/vfutex.c b/arch/arm64/kernel/vdso32/vfutex.c
new file mode 100644
index 000000000000..c47502bbe1d9
--- /dev/null
+++ b/arch/arm64/kernel/vdso32/vfutex.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <linux/stringify.h>
+#include <vdso/futex.h>
+
+#define LABEL(name, sz) __stringify(__futex_list##sz##_try_unlock_cs_##name)
+
+#define GLOBLS(sz) ".globl " LABEL(start, sz) ", " LABEL(success, sz) ", " LABEL(end, sz) "\n"
+
+__u32 __vdso_futex_robust_list32_try_unlock(__u32 *lock, __u32 tid, __u32 *pop)
+{
+	register __u32 *pop_reg asm("r2") = pop, result_reg asm("r3") = 0;
+	__u32 val, zero = 0;
+
+	asm volatile (
+		GLOBLS(32)
+		"retry:						\n"
+		"	ldrex %[val], %[lock]			\n"
+		"	cmp %[tid], %[val]			\n"
+		"	bne " LABEL(end, 32)"			\n"
+		"	strex %[result], %[zero], %[lock]	\n"
+		LABEL(start, 32)":				\n"
+		"	cmp %[result], #0			\n"
+		"	bne retry				\n"
+		LABEL(success, 32)":				\n"
+		"	str %[zero], %[pop_reg]			\n"
+		LABEL(end, 32)":				\n"
+		: [val] "=&r" (val), [result] "=r" (result_reg)
+		: [tid] "r" (tid), [lock] "Q" (*lock), [pop_reg] "Q" (*pop_reg), [zero] "r" (zero)
+		: "memory"
+	);
+
+	return val;
+}

-- 
2.54.0