>From now, by default, (specifically) `int main' in freestanding will
implicitly return 0, as it does for hosted modes. The old behaviour is
still accessible via -fno-builtin-main.
gcc/c-family/ChangeLog:
* c-common.cc (disable_builtin_function): Support special value
`main' that, in freestanding, allows disabling special casing
placed around `main'.
* c-common.h: Add flag_builtin_main.
(want_builtin_main_p): New function, true iff hosted OR
builtin_main are set.
gcc/c/ChangeLog:
* c-decl.cc (grokdeclarator): Consider flag_builtin_main when
deciding whether to emit warnings.
(finish_function): Consider flag_builtin_main when deciding
whether to emit an implicit zero return.
* c-objc-common.cc (c_missing_noreturn_ok_p): Consider missing
noreturn okay only when hosted or when builtin_main is enabled.
gcc/cp/ChangeLog:
* cp-tree.h (DECL_MAIN_P): Consider flag_builtin_main when
deciding whether this function is to be the special function
main.
gcc/ChangeLog:
* doc/invoke.texi: Document -fno-builtin-main.
gcc/testsuite/ChangeLog:
* gcc.dg/c11-noreturn-4.c: Add -fno-builtin-main to options.
* gcc.dg/inline-10.c: Likewise.
* gcc.dg/noreturn-4.c: Likewise.
* g++.dg/freestanding-main-implicitly-returns.C: New test.
* g++.dg/no-builtin-main.C: New test.
* gcc.dg/freestanding-main-implicitly-returns.c: New test.
* gcc.dg/no-builtin-main.c: New test.
Signed-off-by: Arsen Arsenović <ar...@aarsen.me>
---
gcc/c-family/c-common.cc | 6 ++++++
gcc/c-family/c-common.h | 10 ++++++++++
gcc/c/c-decl.cc | 4 ++--
gcc/c/c-objc-common.cc | 9 ++++++---
gcc/cp/cp-tree.h | 12 ++++++-----
gcc/doc/invoke.texi | 20 ++++++++++++++-----
.../freestanding-main-implicitly-returns.C | 5 +++++
gcc/testsuite/g++.dg/no-builtin-main.C | 5 +++++
gcc/testsuite/gcc.dg/c11-noreturn-4.c | 2 +-
.../freestanding-main-implicitly-returns.c | 5 +++++
gcc/testsuite/gcc.dg/inline-10.c | 2 +-
gcc/testsuite/gcc.dg/no-builtin-main.c | 5 +++++
gcc/testsuite/gcc.dg/noreturn-4.c | 2 +-
13 files changed, 69 insertions(+), 18 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/freestanding-main-implicitly-returns.C
create mode 100644 gcc/testsuite/g++.dg/no-builtin-main.C
create mode 100644 gcc/testsuite/gcc.dg/freestanding-main-implicitly-returns.c
create mode 100644 gcc/testsuite/gcc.dg/no-builtin-main.c
diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index 3c60a89bfe2..117db8a1928 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -232,6 +232,10 @@ int flag_isoc2x;
int flag_hosted = 1;
+/* Nonzero means that we want to give main its special meaning */
+
+int flag_builtin_main = 1;
+
/* ObjC language option variables. */
@@ -4878,6 +4882,8 @@ disable_builtin_function (const char *name)
{
if (startswith (name, "__builtin_"))
error ("cannot disable built-in function %qs", name);
+ else if (strcmp("main", name) == 0)
+ flag_builtin_main = 0;
else
{
disabled_builtin *new_disabled_builtin = XNEW (disabled_builtin);
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 5f470d94f4a..cbed5f0f9e8 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -687,6 +687,16 @@ extern int flag_isoc2x;
extern int flag_hosted;
+/* Nonzero means that we want to give main its special meaning */
+
+extern int flag_builtin_main;
+
+/* Returns false if both flag_hosted and flag_builtin_main are zero, true
+ otherwise. */
+inline bool builtin_main_p() {
+ return flag_hosted || flag_builtin_main;
+}
+
/* ObjC language option variables. */
diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index bac8e6cc3f6..5060b3f2a41 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -7695,7 +7695,7 @@ grokdeclarator (const struct c_declarator *declarator,
/* Record presence of `inline' and `_Noreturn', if it is
reasonable. */
- if (flag_hosted && MAIN_NAME_P (declarator->u.id.id))
+ if (builtin_main_p() && MAIN_NAME_P (declarator->u.id.id))
{
if (declspecs->inline_p)
pedwarn (loc, 0, "cannot inline function %<main%>");
@@ -10314,7 +10314,7 @@ finish_function (location_t end_loc)
if (DECL_RESULT (fndecl) && DECL_RESULT (fndecl) != error_mark_node)
DECL_CONTEXT (DECL_RESULT (fndecl)) = fndecl;
- if (MAIN_NAME_P (DECL_NAME (fndecl)) && flag_hosted
+ if (MAIN_NAME_P (DECL_NAME (fndecl)) && builtin_main_p()
&& TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (fndecl)))
== integer_type_node && flag_isoc99)
{
diff --git a/gcc/c/c-objc-common.cc b/gcc/c/c-objc-common.cc
index 70e10a98e33..e229580b182 100644
--- a/gcc/c/c-objc-common.cc
+++ b/gcc/c/c-objc-common.cc
@@ -37,9 +37,12 @@ static bool c_tree_printer (pretty_printer *, text_info *,
const char *,
bool
c_missing_noreturn_ok_p (tree decl)
{
- /* A missing noreturn is not ok for freestanding implementations and
- ok for the `main' function in hosted implementations. */
- return flag_hosted && MAIN_NAME_P (DECL_ASSEMBLER_NAME (decl));
+ /* Missing a return is only okay when flag_builtin_main is enabled, and we
+ are `int main'. */
+ if (!MAIN_NAME_P (DECL_ASSEMBLER_NAME (decl)))
+ return false;
+ return builtin_main_p()
+ && TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (decl))) == integer_type_node;
}
/* Called from check_global_declaration. */
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 67aea9653e3..50751ab74b6 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -771,11 +771,13 @@ typedef struct ptrmem_cst * ptrmem_cst_t;
/* Returns nonzero iff NODE is a declaration for the global function
`main'. */
-#define DECL_MAIN_P(NODE) \
- (DECL_EXTERN_C_FUNCTION_P (NODE) \
- && DECL_NAME (NODE) != NULL_TREE \
- && MAIN_NAME_P (DECL_NAME (NODE)) \
- && flag_hosted)
+#define DECL_MAIN_P(NODE) \
+ (DECL_EXTERN_C_FUNCTION_P (NODE) \
+ && DECL_NAME (NODE) != NULL_TREE \
+ && MAIN_NAME_P (DECL_NAME (NODE)) \
+ && (flag_hosted || (flag_builtin_main \
+ && TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (NODE))) \
+ == integer_type_node)))
/* Lookup walker marking. */
#define LOOKUP_SEEN_P(NODE) TREE_VISITED (NODE)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index a5dc6377835..79f144ec819 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -2537,8 +2537,10 @@ this switch only affects the @code{asm} and
@code{typeof} keywords,
since @code{inline} is a standard keyword in ISO C99.
@item -fno-builtin
+@itemx -fno-builtin-main
@itemx -fno-builtin-@var{function}
@opindex fno-builtin
+@opindex fno-builtin-main
@opindex fbuiltin
@cindex built-in functions
Don't recognize built-in functions that do not begin with
@@ -2577,6 +2579,11 @@ built-in functions selectively when using
@option{-fno-builtin} or
#define strcpy(d, s) __builtin_strcpy ((d), (s))
@end smallexample
+The special form @option{-fno-builtin-main} permits disabling special
+handling of the @code{main} function, such as the implicit zero
+return. This option has no effect in hosted mode (as hosted takes
+precedence over it) and is not implied by @option{-fno-builtin}.
+
@item -fcond-mismatch
@opindex fcond-mismatch
Allow conditional expressions with mismatched types in the second and
@@ -2585,13 +2592,16 @@ is not supported for C++.
@item -ffreestanding
@opindex ffreestanding
+@opindex fno-builtin-main
@cindex hosted environment
Assert that compilation targets a freestanding environment. This
-implies @option{-fno-builtin}. A freestanding environment
-is one in which the standard library may not exist, and program startup may
-not necessarily be at @code{main}. The most obvious example is an OS kernel.
-This is equivalent to @option{-fno-hosted}.
+implies @option{-fno-builtin}. A freestanding environment is one in
+which the standard library may not exist, and program startup may not
+necessarily be at @code{main}. The most obvious example is an OS
+kernel. Note that this option does not imply
+@option{-fno-builtin-main}. @option{-ffreestanding} is equivalent to
+@option{-fno-hosted}.
@xref{Standards,,Language Standards Supported by GCC}, for details of
freestanding and hosted environments.
@@ -5828,7 +5838,7 @@ Options} and @ref{Objective-C and Objective-C++ Dialect
Options}.
-Wimplicit-function-declaration @r{(C and Objective-C only)} @gol
-Winit-self @r{(only for C++)} @gol
-Wlogical-not-parentheses @gol
--Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
+-Wmain @r{(only for C/ObjC and unless} @option{-fno-builtin-main}@r{)} @gol
-Wmaybe-uninitialized @gol
-Wmemset-elt-size @gol
-Wmemset-transposed-args @gol
diff --git a/gcc/testsuite/g++.dg/freestanding-main-implicitly-returns.C
b/gcc/testsuite/g++.dg/freestanding-main-implicitly-returns.C
new file mode 100644
index 00000000000..068ddd4d5ad
--- /dev/null
+++ b/gcc/testsuite/g++.dg/freestanding-main-implicitly-returns.C
@@ -0,0 +1,5 @@
+/* Make sure main is implicitly returned from, even in freestanding. */
+/* { dg-do compile } */
+/* { dg-options "-Wreturn-type -ffreestanding" } */
+
+int main() {}
diff --git a/gcc/testsuite/g++.dg/no-builtin-main.C
b/gcc/testsuite/g++.dg/no-builtin-main.C
new file mode 100644
index 00000000000..7431784d018
--- /dev/null
+++ b/gcc/testsuite/g++.dg/no-builtin-main.C
@@ -0,0 +1,5 @@
+/* Make sure we get warned about missing return with -fno-builtin-main. */
+/* { dg-do compile } */
+/* { dg-options "-Wreturn-type -ffreestanding -fno-builtin-main" } */
+
+int main() {} /* { dg-warning "-Wreturn-type" } */
diff --git a/gcc/testsuite/gcc.dg/c11-noreturn-4.c
b/gcc/testsuite/gcc.dg/c11-noreturn-4.c
index a92a1140f67..16fd8f1b0be 100644
--- a/gcc/testsuite/gcc.dg/c11-noreturn-4.c
+++ b/gcc/testsuite/gcc.dg/c11-noreturn-4.c
@@ -1,6 +1,6 @@
/* Test C11 _Noreturn. Test _Noreturn on main, freestanding. */
/* { dg-do compile } */
-/* { dg-options "-std=c11 -pedantic-errors -ffreestanding" } */
+/* { dg-options "-std=c11 -pedantic-errors -ffreestanding -fno-builtin-main" }
*/
_Noreturn void exit (int);
diff --git a/gcc/testsuite/gcc.dg/freestanding-main-implicitly-returns.c
b/gcc/testsuite/gcc.dg/freestanding-main-implicitly-returns.c
new file mode 100644
index 00000000000..068ddd4d5ad
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/freestanding-main-implicitly-returns.c
@@ -0,0 +1,5 @@
+/* Make sure main is implicitly returned from, even in freestanding. */
+/* { dg-do compile } */
+/* { dg-options "-Wreturn-type -ffreestanding" } */
+
+int main() {}
diff --git a/gcc/testsuite/gcc.dg/inline-10.c b/gcc/testsuite/gcc.dg/inline-10.c
index f7a7592a6a9..bb59f5d81a7 100644
--- a/gcc/testsuite/gcc.dg/inline-10.c
+++ b/gcc/testsuite/gcc.dg/inline-10.c
@@ -1,6 +1,6 @@
/* Test inline main, gnu99 mode, freestanding, -pedantic-errors. */
/* Origin: Joseph Myers <j...@polyomino.org.uk> */
/* { dg-do compile } */
-/* { dg-options "-std=gnu99 -ffreestanding -pedantic-errors" } */
+/* { dg-options "-std=gnu99 -fno-builtin-main -ffreestanding -pedantic-errors"
} */
inline int main (void) { return 1; }
diff --git a/gcc/testsuite/gcc.dg/no-builtin-main.c
b/gcc/testsuite/gcc.dg/no-builtin-main.c
new file mode 100644
index 00000000000..7431784d018
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/no-builtin-main.c
@@ -0,0 +1,5 @@
+/* Make sure we get warned about missing return with -fno-builtin-main. */
+/* { dg-do compile } */
+/* { dg-options "-Wreturn-type -ffreestanding -fno-builtin-main" } */
+
+int main() {} /* { dg-warning "-Wreturn-type" } */
diff --git a/gcc/testsuite/gcc.dg/noreturn-4.c
b/gcc/testsuite/gcc.dg/noreturn-4.c
index 6fe144754d0..c1bdc76b16f 100644
--- a/gcc/testsuite/gcc.dg/noreturn-4.c
+++ b/gcc/testsuite/gcc.dg/noreturn-4.c
@@ -1,6 +1,6 @@
/* Check for "noreturn" warning in main. */
/* { dg-do compile } */
-/* { dg-options "-O2 -Wmissing-noreturn -ffreestanding" } */
+/* { dg-options "-O2 -Wmissing-noreturn -ffreestanding -fno-builtin-main" } */
extern void exit (int) __attribute__ ((__noreturn__));
int
--
2.37.3
