rnk created this revision.
rnk added reviewers: niravd, rsmith, nickdesaulniers.
There aren't any lifetime issues inherent in returning a local label.
Hypothetically, it could be used to drive a state machine driven by
computed goto the next time that same scope is re-entered. In any case,
the Linux kernel uses this code pattern to get PCs, and we don't want to
warn on that code pattern.
Fixes PR38569
https://reviews.llvm.org/D50805
Files:
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaInit.cpp
clang/test/Analysis/stack-addr-ps.cpp
clang/test/Sema/statements.c
Index: clang/test/Sema/statements.c
===================================================================
--- clang/test/Sema/statements.c
+++ clang/test/Sema/statements.c
@@ -29,9 +29,22 @@
}
-void *test10() {
+// PR38569: Clang used to warn on returning the address of a label, but we
don't
+// anymore. Labels aren't exactly destroyed when they go out of scope, and the
+// Linux kernel uses this functionality.
+void *test10() {
bar:
- return &&bar; // expected-warning {{returning address of label, which is
local}}
+ return &&bar;
+}
+
+// Linux actually does something more like this, and we don't want to warn on
+// it.
+void test10_logpc(void*);
+void test10a() {
+ test10_logpc(({
+ my_pc:
+ &&my_pc;
+ }));
}
// PR6034
Index: clang/test/Analysis/stack-addr-ps.cpp
===================================================================
--- clang/test/Analysis/stack-addr-ps.cpp
+++ clang/test/Analysis/stack-addr-ps.cpp
@@ -74,10 +74,12 @@
return &x; // expected-warning{{Address of stack memory associated with
local variable 's1' returned}} expected-warning {{address of stack memory
associated with local variable 's1' returned}}
}
+// PR38569: Clang used to warn when returning label addresses, but now it
+// doesn't.
void *lf() {
label:
- void *const &x = &&label; // expected-note {{binding reference variable
'x' here}}
- return x; // expected-warning {{returning address of label, which is
local}}
+ void *const &x = &&label;
+ return x;
}
template <typename T>
Index: clang/lib/Sema/SemaInit.cpp
===================================================================
--- clang/lib/Sema/SemaInit.cpp
+++ clang/lib/Sema/SemaInit.cpp
@@ -6291,7 +6291,6 @@
/// A temporary or local variable. This will be one of:
/// * A MaterializeTemporaryExpr.
/// * A DeclRefExpr whose declaration is a local.
-/// * An AddrLabelExpr.
/// * A BlockExpr for a block with captures.
using Local = Expr*;
@@ -6735,11 +6734,6 @@
}
break;
- case Stmt::AddrLabelExprClass:
- // We want to warn if the address of a label would escape the function.
- Visit(Path, Local(cast<AddrLabelExpr>(Init)), RK_ReferenceBinding);
- break;
-
default:
break;
}
@@ -6923,8 +6917,6 @@
<< isa<ParmVarDecl>(DRE->getDecl()) << DiagRange;
} else if (isa<BlockExpr>(L)) {
Diag(DiagLoc, diag::err_ret_local_block) << DiagRange;
- } else if (isa<AddrLabelExpr>(L)) {
- Diag(DiagLoc, diag::warn_ret_addr_label) << DiagRange;
} else {
Diag(DiagLoc, diag::warn_ret_local_temp_addr_ref)
<< Entity.getType()->isReferenceType() << DiagRange;
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7869,9 +7869,6 @@
def warn_ret_local_temp_addr_ref : Warning<
"returning %select{address of|reference to}0 local temporary object">,
InGroup<ReturnStackAddress>;
-def warn_ret_addr_label : Warning<
- "returning address of label, which is local">,
- InGroup<ReturnStackAddress>;
def err_ret_local_block : Error<
"returning block that lives on the local stack">;
def note_local_var_initializer : Note<
Index: clang/test/Sema/statements.c
===================================================================
--- clang/test/Sema/statements.c
+++ clang/test/Sema/statements.c
@@ -29,9 +29,22 @@
}
-void *test10() {
+// PR38569: Clang used to warn on returning the address of a label, but we don't
+// anymore. Labels aren't exactly destroyed when they go out of scope, and the
+// Linux kernel uses this functionality.
+void *test10() {
bar:
- return &&bar; // expected-warning {{returning address of label, which is local}}
+ return &&bar;
+}
+
+// Linux actually does something more like this, and we don't want to warn on
+// it.
+void test10_logpc(void*);
+void test10a() {
+ test10_logpc(({
+ my_pc:
+ &&my_pc;
+ }));
}
// PR6034
Index: clang/test/Analysis/stack-addr-ps.cpp
===================================================================
--- clang/test/Analysis/stack-addr-ps.cpp
+++ clang/test/Analysis/stack-addr-ps.cpp
@@ -74,10 +74,12 @@
return &x; // expected-warning{{Address of stack memory associated with local variable 's1' returned}} expected-warning {{address of stack memory associated with local variable 's1' returned}}
}
+// PR38569: Clang used to warn when returning label addresses, but now it
+// doesn't.
void *lf() {
label:
- void *const &x = &&label; // expected-note {{binding reference variable 'x' here}}
- return x; // expected-warning {{returning address of label, which is local}}
+ void *const &x = &&label;
+ return x;
}
template <typename T>
Index: clang/lib/Sema/SemaInit.cpp
===================================================================
--- clang/lib/Sema/SemaInit.cpp
+++ clang/lib/Sema/SemaInit.cpp
@@ -6291,7 +6291,6 @@
/// A temporary or local variable. This will be one of:
/// * A MaterializeTemporaryExpr.
/// * A DeclRefExpr whose declaration is a local.
-/// * An AddrLabelExpr.
/// * A BlockExpr for a block with captures.
using Local = Expr*;
@@ -6735,11 +6734,6 @@
}
break;
- case Stmt::AddrLabelExprClass:
- // We want to warn if the address of a label would escape the function.
- Visit(Path, Local(cast<AddrLabelExpr>(Init)), RK_ReferenceBinding);
- break;
-
default:
break;
}
@@ -6923,8 +6917,6 @@
<< isa<ParmVarDecl>(DRE->getDecl()) << DiagRange;
} else if (isa<BlockExpr>(L)) {
Diag(DiagLoc, diag::err_ret_local_block) << DiagRange;
- } else if (isa<AddrLabelExpr>(L)) {
- Diag(DiagLoc, diag::warn_ret_addr_label) << DiagRange;
} else {
Diag(DiagLoc, diag::warn_ret_local_temp_addr_ref)
<< Entity.getType()->isReferenceType() << DiagRange;
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7869,9 +7869,6 @@
def warn_ret_local_temp_addr_ref : Warning<
"returning %select{address of|reference to}0 local temporary object">,
InGroup<ReturnStackAddress>;
-def warn_ret_addr_label : Warning<
- "returning address of label, which is local">,
- InGroup<ReturnStackAddress>;
def err_ret_local_block : Error<
"returning block that lives on the local stack">;
def note_local_var_initializer : Note<
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