[PATCH v2 1/1] plugins: use int64_t for the syscall filter return value

[Ziyang Zhang <functioner@sjtu.edu.cn>]

The syscall return value passed back through the syscall filter
callback is semantically signed: negative values encode errno codes.
Declaring the sysret pointer as uint64_t * is therefore misleading and
forces callers to launder the value through an unsigned temporary.

Change the sysret pointer to int64_t * across the public plugin API
typedef (qemu_plugin_vcpu_syscall_filter_cb_t), the internal
qemu_plugin_vcpu_syscall_filter() prototypes and stub, its
implementation in plugins/core.c, the linux-user caller, and the
in-tree example plugins.

Signed-off-by: Ziyang Zhang <functioner@sjtu.edu.cn>
---
v2: rebased onto current master. The syscall callbacks now take a
    userdata argument, so the filter signatures were adjusted to keep
    that while changing only the sysret type. No functional change.
---
 include/plugins/qemu-plugin.h | 2 +-
 include/qemu/plugin.h         | 4 ++--
 linux-user/syscall.c          | 2 +-
 plugins/core.c                | 2 +-
 tests/tcg/plugins/setpc.c     | 2 +-
 tests/tcg/plugins/syscall.c   | 2 +-
 6 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/plugins/qemu-plugin.h b/include/plugins/qemu-plugin.h
index d8d4b37384..3e913cd89c 100644
--- a/include/plugins/qemu-plugin.h
+++ b/include/plugins/qemu-plugin.h
@@ -871,7 +871,7 @@ typedef bool
                                         int64_t num, uint64_t a1, uint64_t a2,
                                         uint64_t a3, uint64_t a4, uint64_t a5,
                                         uint64_t a6, uint64_t a7, uint64_t a8,
-                                        uint64_t *sysret,
+                                        int64_t *sysret,
                                         void *userdata);
 
 /**
diff --git a/include/qemu/plugin.h b/include/qemu/plugin.h
index 9356ee836a..9c2ec8ceae 100644
--- a/include/qemu/plugin.h
+++ b/include/qemu/plugin.h
@@ -172,7 +172,7 @@ bool
 qemu_plugin_vcpu_syscall_filter(CPUState *cpu, int64_t num, uint64_t a1,
                                 uint64_t a2, uint64_t a3, uint64_t a4,
                                 uint64_t a5, uint64_t a6, uint64_t a7,
-                                uint64_t a8, uint64_t *sysret);
+                                uint64_t a8, int64_t *sysret);
 
 void qemu_plugin_vcpu_mem_cb(CPUState *cpu, uint64_t vaddr,
                              uint64_t value_low,
@@ -288,7 +288,7 @@ static inline bool
 qemu_plugin_vcpu_syscall_filter(CPUState *cpu, int64_t num, uint64_t a1,
                                 uint64_t a2, uint64_t a3, uint64_t a4,
                                 uint64_t a5, uint64_t a6, uint64_t a7,
-                                uint64_t a8, uint64_t *sysret)
+                                uint64_t a8, int64_t *sysret)
 {
     return false;
 }
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index fbe357b7e0..d257fb9ca9 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -14619,7 +14619,7 @@ static bool send_through_syscall_filters(CPUState *cpu, int num,
                                          abi_long arg7, abi_long arg8,
                                          abi_long *sysret)
 {
-    uint64_t sysret64 = 0;
+    int64_t sysret64 = 0;
     bool filtered = qemu_plugin_vcpu_syscall_filter(cpu, num, arg1, arg2,
                                                     arg3, arg4, arg5, arg6,
                                                     arg7, arg8, &sysret64);
diff --git a/plugins/core.c b/plugins/core.c
index 4b55aacd2d..1113bfe567 100644
--- a/plugins/core.c
+++ b/plugins/core.c
@@ -573,7 +573,7 @@ bool
 qemu_plugin_vcpu_syscall_filter(CPUState *cpu, int64_t num, uint64_t a1,
                                 uint64_t a2, uint64_t a3, uint64_t a4,
                                 uint64_t a5, uint64_t a6, uint64_t a7,
-                                uint64_t a8, uint64_t *sysret)
+                                uint64_t a8, int64_t *sysret)
 {
     struct qemu_plugin_cb *cb, *next;
     enum qemu_plugin_event ev = QEMU_PLUGIN_EV_VCPU_SYSCALL_FILTER;
diff --git a/tests/tcg/plugins/setpc.c b/tests/tcg/plugins/setpc.c
index 7c78f182f0..76b2efc61b 100644
--- a/tests/tcg/plugins/setpc.c
+++ b/tests/tcg/plugins/setpc.c
@@ -27,7 +27,7 @@ static bool vcpu_syscall_filter(unsigned int vcpu_index,
                                 int64_t num, uint64_t a1, uint64_t a2,
                                 uint64_t a3, uint64_t a4, uint64_t a5,
                                 uint64_t a6, uint64_t a7, uint64_t a8,
-                                uint64_t *sysret, void *userdata)
+                                int64_t *sysret, void *userdata)
 {
     if (num == MAGIC_SYSCALL) {
         if (a1 == SETPC) {
diff --git a/tests/tcg/plugins/syscall.c b/tests/tcg/plugins/syscall.c
index a28d108784..debec9f09b 100644
--- a/tests/tcg/plugins/syscall.c
+++ b/tests/tcg/plugins/syscall.c
@@ -176,7 +176,7 @@ static bool vcpu_syscall_filter(unsigned int vcpu_index,
                                 int64_t num, uint64_t a1, uint64_t a2,
                                 uint64_t a3, uint64_t a4, uint64_t a5,
                                 uint64_t a6, uint64_t a7, uint64_t a8,
-                                uint64_t *sysret, void *userdata)
+                                int64_t *sysret, void *userdata)
 {
     /* Special syscall to test the filter functionality. */
     if (num == 4096 && a1 == 0x66CCFF) {
-- 
2.34.1