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RFC: BC-ABI version IDs, take 2
- From: Bryce McKinlay <mckinlay at redhat dot com>
- To: java-patches at gcc dot gnu dot org
- Date: Fri, 20 May 2005 19:28:27 -0400
- Subject: RFC: BC-ABI version IDs, take 2
Here's another version ID patch. The basic changes are:
- From the 32-bit version ID, we use 20 bits for a numerical version
number. For the C++ ABI, this is calculated from the major and minor GCC
version numbers. For the BC ABI, this number could be arbritary, but I
think there is some value in using a number which relates to the first
GCC version that ABI is compatible with. It avoids the need to maintain
a table somewhere mapping version IDs to specific GCJ releases, and if
we were to print some error message if a class with an incompatible
version ID is loaded, then a useful error message can be derived from
the version ID.
- 2 digits in the version number are reserved for a "minor ABI version".
This could be used in the event that an addition/change to the ABI is
made during a GCC release cycle.
- The remaining 12 bits are reserved for flags that could represent
various ABI features, or just additional ABI-specific options. Currently
2 flags are defined:
FLAG_BINARYCOMPAT_ABI
FLAG_BOOTSTRAP_LOADER
This scheme should give us a more flexible and scalable ID number going
forward. Comments?
Bryce
2005-05-20 Bryce McKinlay <mckinlay@redhat.com>
* decl.c (GCJ_BINARYCOMPAT_ADDITION,
GCJ_BOOTSTRAP_LOADER_ADDITION): Removed.
(FLAG_BINARYCOMPAT_ABI, FLAG_BOOTSTRAP_LOADER,
MINOR_BINARYCOMPAT_ABI_VERSION): New.
(GCJ_CURRENT_BC_ABI_VERSION): Use new method to calculate version ID.
(parse_version): Calculate version ID using new method. Use bit-flags
for flag_indirect_dispatch and flag_bootstrap_classes.
2005-05-20 Bryce McKinlay <mckinlay@redhat.com>
* include/jvm.h (FLAG_BINARYCOMPAT_ABI, FLAG_BOOTSTRAP_LOADER): New.
(GCJ_BINARYCOMPAT_ADDITION, GCJ_BOOTSTRAP_LOADER_ADDITION): Removed.
(OLD_GCJ_40_BC_ABI_VERSION): Renamed. Old-style version ID for BC-ABI
classes.
(GCJ_40_BC_ABI_VERSION, GCJ_41_BC_ABI_VERSION): New. Calculate version
IDs using new method.
(_Jv_CheckABIVersion): Check for both old and new style version IDs.
(_Jv_ClassForBootstrapLoader): Use FLAG_BOOTSTRAP_LOADER.
Index: gcc/java/decl.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/java/decl.c,v
retrieving revision 1.220
diff -u -r1.220 decl.c
--- gcc/java/decl.c 12 May 2005 01:26:50 -0000 1.220
+++ gcc/java/decl.c 20 May 2005 22:59:36 -0000
@@ -61,19 +61,31 @@
static tree check_local_unnamed_variable (tree, tree, tree);
static void parse_version (void);
-/* Used when computing the ABI version. */
-#define GCJ_BINARYCOMPAT_ADDITION 5
-/* Used when defining a class that should be loaded by the bootstrap
- loader. */
-#define GCJ_BOOTSTRAP_LOADER_ADDITION 1
-
-/* The version of the BC ABI that we generate. At the moment we are
- compatible with what shipped in GCC 4.0. This must be kept in sync
- with parse_version(), libgcj, and reality (if the BC format
- changes, this must change. */
+/* The following ABI flags are used in the high-order bits of the version
+ ID field. The version ID number itself should never be larger than
+ 0xfffff, so it should be safe to use top 12 bits for these flags. */
+
+#define FLAG_BINARYCOMPAT_ABI (1<<31) /* Class is built with the BC-ABI. */
+
+#define FLAG_BOOTSTRAP_LOADER (1<<30) /* Used when defining a class that
+ should be loaded by the bootstrap
+ loader. */
+
+/* If an ABI change is made within a GCC release series, rendering current
+ binaries incompatible with the old runtimes, this number can be set to
+ enforce the compatibility rules. */
+#define MINOR_BINARYCOMPAT_ABI_VERSION 0
+
+/* The runtime may recognize a variety of BC ABIs (objects generated by
+ different version of gcj), but will probably always require strict
+ matching for the ordinary (C++) ABI. */
+
+/* The version ID of the BC ABI that we generate. This must be kept in
+ sync with parse_version(), libgcj, and reality (if the BC format changes,
+ this must change). */
#define GCJ_CURRENT_BC_ABI_VERSION \
- (4 * 10000 + 0 * 10 + GCJ_BINARYCOMPAT_ADDITION)
+ (4 * 100000 + 1 * 1000 + MINOR_BINARYCOMPAT_ABI_VERSION)
/* The ABI version number. */
tree gcj_abi_version;
@@ -614,18 +626,20 @@
++p;
}
- /* Implicit in this computation is the idea that we won't break the
- old-style binary ABI in a sub-minor release (e.g., from 4.0.0 to
- 4.0.1). */
- abi_version = 10000 * major + 10 * minor;
- /* It is helpful to distinguish BC ABI from ordinary ABI at this
- level, since at some point we will recognize a variety of BC ABIs
- (objects generated by different version of gcj), but will
- probably always require strict matching for ordinary ABI. */
if (flag_indirect_dispatch)
- abi_version = GCJ_CURRENT_BC_ABI_VERSION;
+ {
+ abi_version = GCJ_CURRENT_BC_ABI_VERSION;
+ abi_version |= FLAG_BINARYCOMPAT_ABI;
+ }
+ else /* C++ ABI */
+ {
+ /* Implicit in this computation is the idea that we won't break the
+ old-style binary ABI in a sub-minor release (e.g., from 4.0.0 to
+ 4.0.1). */
+ abi_version = 100000 * major + 1000 * minor;
+ }
if (flag_bootstrap_classes)
- abi_version += GCJ_BOOTSTRAP_LOADER_ADDITION;
+ abi_version |= FLAG_BOOTSTRAP_LOADER;
gcj_abi_version = build_int_cstu (ptr_type_node, abi_version);
}
Index: libjava/include/jvm.h
===================================================================
RCS file: /cvs/gcc/gcc/libjava/include/jvm.h,v
retrieving revision 1.86
diff -u -r1.86 jvm.h
--- libjava/include/jvm.h 13 May 2005 01:02:32 -0000 1.86
+++ libjava/include/jvm.h 20 May 2005 22:59:36 -0000
@@ -564,31 +564,54 @@
extern void _Jv_RegisterBootstrapPackages ();
+#define FLAG_BINARYCOMPAT_ABI (1<<31) /* Class is built with the BC-ABI. */
+
+#define FLAG_BOOTSTRAP_LOADER (1<<30) /* Used when defining a class that
+ should be loaded by the bootstrap
+ loader. */
+
+// These are used to find ABI versions we recognize.
+#define GCJ_VERSION (__GNUC__ * 100000 + __GNUC_MINOR__ * 1000)
+
+// This is the old-style BC version ID used by GCJ 4.0.
+#define OLD_GCJ_40_BC_ABI_VERSION (4 * 10000 + 0 * 10 + 5)
+
+// New style version IDs used by GCJ 4.0.1 and later.
+#define GCJ_40_BC_ABI_VERSION (4 * 100000 + 0 * 1000)
+#define GCJ_41_BC_ABI_VERSION (4 * 100000 + 1 * 1000)
-// This is used to find ABI versions we recognize.
-#define GCJ_VERSION (__GNUC__ * 10000 + __GNUC_MINOR__ * 10)
-#define GCJ_BINARYCOMPAT_ADDITION 5
-#define GCJ_BOOTSTRAP_LOADER_ADDITION 1
-
-// At present we know we are compatible with the BC ABI as used in GCC
-// 4.0.
-#define GCJ_40_BC_ABI_VERSION (4 * 10000 + 0 * 10 + GCJ_BINARYCOMPAT_ADDITION)
inline bool
_Jv_CheckABIVersion (unsigned long value)
{
- // Recognize our defined C++ ABIs.
- return (value == GCJ_VERSION
- || value == (GCJ_VERSION + GCJ_BOOTSTRAP_LOADER_ADDITION)
- || value == GCJ_40_BC_ABI_VERSION
- || value == (GCJ_40_BC_ABI_VERSION + GCJ_BOOTSTRAP_LOADER_ADDITION));
+ // We are compatible with GCJ 4.0 BC-ABI classes. This release used a
+ // different format for the version ID string.
+ if (value == OLD_GCJ_40_BC_ABI_VERSION)
+ return true;
+
+ // The 20 low-end bits are used for the version number.
+ unsigned long version = value & 0xfffff;
+
+ if (value & FLAG_BINARYCOMPAT_ABI)
+ {
+ int abi_rev = version % 100;
+ int abi_ver = version - abi_rev;
+ if (abi_ver == GCJ_40_BC_ABI_VERSION && abi_rev <= 0)
+ return true;
+ if (abi_ver == GCJ_41_BC_ABI_VERSION && abi_rev <= 0)
+ return true;
+ }
+ else
+ // C++ ABI
+ return version == GCJ_VERSION;
+
+ return false;
}
inline bool
_Jv_ClassForBootstrapLoader (unsigned long value)
{
- return (value == (GCJ_VERSION + GCJ_BOOTSTRAP_LOADER_ADDITION)
- || value == (GCJ_40_BC_ABI_VERSION + GCJ_BOOTSTRAP_LOADER_ADDITION));
+ return (value & FLAG_BOOTSTRAP_LOADER);
}
// It makes the source cleaner if we simply always define this