error: Eliminate error_propagate() with Coccinelle, part 1

When all we do with an Error we receive into a local variable is
propagating to somewhere else, we can just as well receive it there
right away.  Convert

    if (!foo(..., &err)) {
        ...
        error_propagate(errp, err);
        ...
        return ...
    }

to

    if (!foo(..., errp)) {
        ...
        ...
        return ...
    }

where nothing else needs @err.  Coccinelle script:

    @rule1 forall@
    identifier fun, err, errp, lbl;
    expression list args, args2;
    binary operator op;
    constant c1, c2;
    symbol false;
    @@
         if (
    (
    -        fun(args, &err, args2)
    +        fun(args, errp, args2)
    |
    -        !fun(args, &err, args2)
    +        !fun(args, errp, args2)
    |
    -        fun(args, &err, args2) op c1
    +        fun(args, errp, args2) op c1
    )
            )
         {
             ... when != err
                 when != lbl:
                 when strict
    -        error_propagate(errp, err);
             ... when != err
    (
             return;
    |
             return c2;
    |
             return false;
    )
         }

    @rule2 forall@
    identifier fun, err, errp, lbl;
    expression list args, args2;
    expression var;
    binary operator op;
    constant c1, c2;
    symbol false;
    @@
    -    var = fun(args, &err, args2);
    +    var = fun(args, errp, args2);
         ... when != err
         if (
    (
             var
    |
             !var
    |
             var op c1
    )
            )
         {
             ... when != err
                 when != lbl:
                 when strict
    -        error_propagate(errp, err);
             ... when != err
    (
             return;
    |
             return c2;
    |
             return false;
    |
             return var;
    )
         }

    @depends on rule1 || rule2@
    identifier err;
    @@
    -    Error *err = NULL;
         ... when != err

Not exactly elegant, I'm afraid.

The "when != lbl:" is necessary to avoid transforming

         if (fun(args, &err)) {
             goto out
         }
         ...
     out:
         error_propagate(errp, err);

even though other paths to label out still need the error_propagate().
For an actual example, see sclp_realize().

Without the "when strict", Coccinelle transforms vfio_msix_setup(),
incorrectly.  I don't know what exactly "when strict" does, only that
it helps here.

The match of return is narrower than what I want, but I can't figure
out how to express "return where the operand doesn't use @err".  For
an example where it's too narrow, see vfio_intx_enable().

Silently fails to convert hw/arm/armsse.c, because Coccinelle gets
confused by ARMSSE being used both as typedef and function-like macro
there.  Converted manually.

Line breaks tidied up manually.  One nested declaration of @local_err
deleted manually.  Preexisting unwanted blank line dropped in
hw/riscv/sifive_e.c.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200707160613.848843-35-armbru@redhat.com>

2 files changed, 4 insertions, 11 deletions

diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 343c227c09..15494002d2 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -464,11 +464,9 @@ static void cpu_max_set_sve_max_vq(Object *obj, Visitor *v, const char *name,
                                    void *opaque, Error **errp)
 {
     ARMCPU *cpu = ARM_CPU(obj);
-    Error *err = NULL;
     uint32_t max_vq;
 
-    if (!visit_type_uint32(v, name, &max_vq, &err)) {
-        error_propagate(errp, err);
+    if (!visit_type_uint32(v, name, &max_vq, errp)) {
         return;
     }
 
@@ -509,11 +507,9 @@ static void cpu_arm_set_sve_vq(Object *obj, Visitor *v, const char *name,
 {
     ARMCPU *cpu = ARM_CPU(obj);
     uint32_t vq = atoi(&name[3]) / 128;
-    Error *err = NULL;
     bool value;
 
-    if (!visit_type_bool(v, name, &value, &err)) {
-        error_propagate(errp, err);
+    if (!visit_type_bool(v, name, &value, errp)) {
         return;
     }
 
@@ -544,12 +540,10 @@ static void cpu_arm_set_sve(Object *obj, Visitor *v, const char *name,
                             void *opaque, Error **errp)
 {
     ARMCPU *cpu = ARM_CPU(obj);
-    Error *err = NULL;
     bool value;
     uint64_t t;
 
-    if (!visit_type_bool(v, name, &value, &err)) {
-        error_propagate(errp, err);
+    if (!visit_type_bool(v, name, &value, errp)) {
         return;
     }
 
diff --git a/target/arm/monitor.c b/target/arm/monitor.c
index c162c5fb68..ba6e01abd0 100644
--- a/target/arm/monitor.c
+++ b/target/arm/monitor.c
@@ -174,10 +174,9 @@ CpuModelExpansionInfo *qmp_query_cpu_model_expansion(CpuModelExpansionType type,
         Error *err = NULL;
 
         visitor = qobject_input_visitor_new(model->props);
-        if (!visit_start_struct(visitor, NULL, NULL, 0, &err)) {
+        if (!visit_start_struct(visitor, NULL, NULL, 0, errp)) {
             visit_free(visitor);
             object_unref(obj);
-            error_propagate(errp, err);
             return NULL;
         }