glibc: improve RISC-V support

* omit crti.o / crtn.o for this architecture
 * add missing entry.h header from upstream

lib/libc/glibc/sysdeps/generic/entry.h

@@ -0,0 +1,5 @@
+#ifndef __ASSEMBLY__
+extern void _start (void) attribute_hidden;
+#endif
+
+#define ENTRY_POINT _start

lib/libc/glibc/sysdeps/hppa/entry.h

@@ -0,0 +1,13 @@
+#ifndef __ASSEMBLY__
+extern void _start (void);
+#endif
+
+/* Lives in libgcc.so and canonicalizes function pointers for comparison.  */
+extern unsigned int __canonicalize_funcptr_for_compare (unsigned int fptr);
+
+/* The function's entry point is stored in the first word of the
+   function descriptor (plabel) of _start().  */
+#define ENTRY_POINT __canonicalize_funcptr_for_compare((unsigned int)_start)
+
+/* We have to provide a special declaration.  */
+#define ENTRY_POINT_DECL(class) class void _start (void);

lib/libc/glibc/sysdeps/ia64/entry.h

@@ -0,0 +1,13 @@
+#include <link.h>
+#include <dl-fptr.h>
+
+#ifndef __ASSEMBLY__
+extern void _start (void);
+#endif
+
+/* The function's entry point is stored in the first word of the
+   function descriptor (plabel) of _start().  */
+#define ENTRY_POINT ELF_PTR_TO_FDESC (_start)->ip
+
+/* We have to provide a special declaration.  */
+#define ENTRY_POINT_DECL(class) class void _start (void);

lib/libc/glibc/sysdeps/powerpc/powerpc64/entry.h

@@ -0,0 +1,37 @@
+/* Finding the entry point and start of text.  PowerPC64 version.
+   Copyright (C) 2002-2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+
+#ifndef __ASSEMBLY__
+extern void _start (void);
+#endif
+
+#define ENTRY_POINT _start
+
+#if _CALL_ELF != 2
+/* We have to provide a special declaration.  */
+#define ENTRY_POINT_DECL(class) class void _start (void);
+
+/* Use the address of ._start as the lowest address for which we need
+   to keep profiling records.  We can't copy the ia64 scheme as our
+   entry poiny address is really the address of the function
+   descriptor, not the actual function entry.  */
+#define TEXT_START \
+  ({ extern unsigned long int _start_as_data[] asm ("_start");  \
+     _start_as_data[0]; })
+#endif

lib/libc/glibc/sysdeps/unix/mips/entry.h

@@ -0,0 +1,5 @@
+#ifndef __ASSEMBLY__
+extern void __start (void);
+#endif
+
+#define ENTRY_POINT __start

src/Compilation.zig

@@ -1586,7 +1586,17 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
         // If we need to build glibc for the target, add work items for it.
         // We go through the work queue so that building can be done in parallel.
         if (comp.wantBuildGLibCFromSource()) {
-            try comp.addBuildingGLibCJobs();
+            if (glibc.needsCrtiCrtn(comp.getTarget())) {
+                try comp.work_queue.write(&[_]Job{
+                    .{ .glibc_crt_file = .crti_o },
+                    .{ .glibc_crt_file = .crtn_o },
+                });
+            }
+            try comp.work_queue.write(&[_]Job{
+                .{ .glibc_crt_file = .scrt1_o },
+                .{ .glibc_crt_file = .libc_nonshared_a },
+                .{ .glibc_shared_objects = {} },
+            });
         }
         if (comp.wantBuildMuslFromSource()) {
             try comp.work_queue.ensureUnusedCapacity(6);
@@ -4046,16 +4056,6 @@ pub fn get_libc_crt_file(comp: *Compilation, arena: Allocator, basename: []const
     return full_path;
 }
 
-fn addBuildingGLibCJobs(comp: *Compilation) !void {
-    try comp.work_queue.write(&[_]Job{
-        .{ .glibc_crt_file = .crti_o },
-        .{ .glibc_crt_file = .crtn_o },
-        .{ .glibc_crt_file = .scrt1_o },
-        .{ .glibc_crt_file = .libc_nonshared_a },
-        .{ .glibc_shared_objects = {} },
-    });
-}
-
 fn wantBuildLibCFromSource(comp: Compilation) bool {
     const is_exe_or_dyn_lib = switch (comp.bin_file.options.output_mode) {
         .Obj => false,

src/glibc.zig

@@ -1062,3 +1062,11 @@ fn buildSharedLib(
 
     try sub_compilation.updateSubCompilation();
 }
+
+// Return true if glibc has crti/crtn sources for that architecture.
+pub fn needsCrtiCrtn(target: std.Target) bool {
+    return switch (target.cpu.arch) {
+        .riscv32, .riscv64 => false,
+        else => true,
+    };
+}