Commit 5dd2bb525d1f19969c450c2b99a71f866a4f01ff | zig

author	Alex Rønne Petersen <alex@alexrp.com> 2024-08-17 11:42:32+02:00
committer	Andrew Kelley <andrew@ziglang.org> 2024-08-23 11:09:20-07:00
log	5dd2bb525d1f19969c450c2b99a71f866a4f01ff
tree	3dac4b3d3d5facfdb2c8998ff50a45bfa0015da2
parent	df6907f6019ec178735f06e1b55cef6a90234201

glibc: Define _IO_stdin_used in start code and reference it in stub asm.

This is necessary to inform the real, non-stub glibc that a program built with
Zig is using a modern `FILE` structure, i.e. glibc 2.1+. This is particularly
important on lesser-used architectures where the legacy code is poorly tested;
for example, glibc 2.40 introduced a regression for the legacy case in the
libio cleanup code, causing all Zig-compiled MIPS binaries to crash on exit.

2 files changed, 59 insertions(+), 1 deletions(-)

lib
- libc
  - glibc
    csu
    init.c
src
- glibc.zig

lib/libc/glibc/csu/init.c created+23

...	...	@@ -0,0 +1,23 @@
	1	/* Special startup support.
	2	Copyright (C) 1997-2024 Free Software Foundation, Inc.
	3	This file is part of the GNU C Library.
	4
	5	The GNU C Library is free software; you can redistribute it and/or
	6	modify it under the terms of the GNU Lesser General Public
	7	License as published by the Free Software Foundation; either
	8	version 2.1 of the License, or (at your option) any later version.
	9
	10	The GNU C Library is distributed in the hope that it will be useful,
	11	but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	13	Lesser General Public License for more details.
	14
	15	You should have received a copy of the GNU Lesser General Public
	16	License along with the GNU C Library; if not, see
	17	<https://www.gnu.org/licenses/>. */
	18
	19	/* Vestigial libio version number. Some code in libio checks whether
	20	this symbol exists in the executable, but nothing looks at its
	21	value anymore; the value it was historically set to has been
	22	preserved out of an abundance of caution. */
	23	const int _IO_stdin_used = 0x20001;

src/glibc.zig+36-1

...	...	@@ -286,7 +286,11 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile, prog_node: std.Progre
286	286	.owner = undefined,
287	287	};
288	288	};
289		var files = [_]Compilation.CSourceFile{ start_o, abi_note_o };
	289	const init_o: Compilation.CSourceFile = .{
	290	.src_path = try lib_path(comp, arena, lib_libc_glibc ++ "csu" ++ path.sep_str ++ "init.c"),
	291	.owner = undefined,
	292	};
	293	var files = [_]Compilation.CSourceFile{ start_o, abi_note_o, init_o };
290	294	return comp.build_crt_file("Scrt1", .Obj, .@"glibc Scrt1.o", prog_node, &files);
291	295	},
292	296	.libc_nonshared_a => {
...	...	@@ -682,6 +686,12 @@ pub const BuiltSharedObjects = struct {
682	686
683	687	const all_map_basename = "all.map";
684	688
	689	fn wordDirective(target: std.Target) []const u8 {
	690	// Based on its description in the GNU `as` manual, you might assume that `.word` is sized
	691	// according to the target word size. But no; that would just make too much sense.
	692	return if (target.ptrBitWidth() == 64) ".quad" else ".long";
	693	}
	694
685	695	pub fn buildSharedObjects(comp: *Compilation, prog_node: std.Progress.Node) !void {
686	696	const tracy = trace(@src());
687	697	defer tracy.end();
...	...	@@ -923,6 +933,31 @@ pub fn buildSharedObjects(comp: *Compilation, prog_node: std.Progress.Node) !voi
923	933
924	934	try stubs_asm.appendSlice(".data\n");
925	935
	936	// For some targets, the real `libc.so.6` will contain a weak reference to `_IO_stdin_used`,
	937	// making the linker put the symbol in the dynamic symbol table. We likewise need to emit a
	938	// reference to it here for that effect, or it will not show up, which in turn will cause
	939	// the real glibc to think that the program was built against an ancient `FILE` structure
	940	// (pre-glibc 2.1).
	941	//
	942	// Note that glibc only compiles in the legacy compatibility code for some targets; it
	943	// depends on what is defined in the `shlib-versions` file for the particular architecture
	944	// and ABI. Those files are preprocessed by 2 separate tools during the glibc build to get
	945	// the final `abi-versions.h`, so it would be quite brittle to try to condition our emission
	946	// of the `_IO_stdin_used` reference in the exact same way. The only downside of emitting
	947	// the reference unconditionally is that it ends up being unused for newer targets; it
	948	// otherwise has no negative effect.
	949	//
	950	// glibc uses a weak reference because it has to work with programs compiled against pre-2.1
	951	// versions where the symbol didn't exist. We only care about modern glibc versions, so use
	952	// a strong reference.
	953	if (std.mem.eql(u8, lib.name, "c")) {
	954	try stubs_asm.writer().print(
	955	\\.globl _IO_stdin_used
	956	\\{s} _IO_stdin_used
	957	\\
	958	, .{wordDirective(target)});
	959	}
	960
926	961	const obj_inclusions_len = mem.readInt(u16, metadata.inclusions[inc_i..][0..2], .little);
927	962	inc_i += 2;
928	963