`-lc` doesn't link `c_nonshared` #11137

Vexu · 2022-03-12T16:32:17Z

$ cat a.c
extern char __libc_single_threaded;
int main(void) {
    return __libc_single_threaded;
}
$ clang a.c
$ zig build-exe a.c -lc
ld.lld: error: undefined symbol: __libc_single_threaded
>>> referenced by a.c:3
>>>               /home/vexu/.cache/zig/o/00d791557252b46f5ed6668a930dc12a/a.o:(main)
error: LLDReportedFailure

Not sure how this works on other targets but on Arch Linux it means that building stage2 with system LLVM requires this patch:

diff --git a/build.zig b/build.zig
index 5896ab1a8..fb821ccf4 100644
--- a/build.zig
+++ b/build.zig
@@ -550,6 +550,7 @@ fn addCmakeCfgOptionsToExe(
                 else => |e| return e,
             };
             exe.linkSystemLibrary("unwind");
+            exe.linkSystemLibrary("c_nonshared");
         } else if (exe.target.isFreeBSD()) {
             try addCxxKnownPath(b, cfg, exe, "libc++.a", null, need_cpp_includes);
             exe.linkSystemLibrary("pthread");

Prior to this commit, building on Arch Linux would result in the following linker error: undefined symbol: __libc_single_threaded Updates ziglang#11137.

daurnimator · 2022-04-26T09:40:08Z

Arch uses glibc 2.35.

Looking through recent glibc changes related to c_nonshared I found bminor/glibc@1a2f44a. I wonder if this means that linking pthread previously implied c_nonshared, but it doesn't any more.

ifreund · 2022-04-26T09:45:40Z

The proper fix is probably adding -lc_nonshared to libcFullLinkFlags() in src/target.zig if targeting glibc. I would like to understand exactly what's happening here though before doing that.

matu3ba · 2022-05-13T09:29:15Z

At least for me a default build of glibc contains libc_nonshared.a, but srcglibc.zig` does not contain it in the library list:

// The order of the elements in this array defines the linking order.
pub const libs = [_]Lib{
    .{ .name = "m", .sover = 6 },
    .{ .name = "pthread", .sover = 0 },
    .{ .name = "c", .sover = 6 },
    .{ .name = "dl", .sover = 2 },
    .{ .name = "rt", .sover = 1 },
    .{ .name = "ld", .sover = 2 },
    .{ .name = "util", .sover = 1 },
};

Nevertheless, libc_nonshared.a is generated during building stage1.

How is Zig picking up the correct paths to the libcs etc in .cache? rg glibc inside the build folder of stage1 shows no results. Is the path picked up from calculating/combining some hashes?

andrewrk · 2022-05-13T21:44:53Z

Note that zig is perfectly capable of providing libc_nonshared.a... but in the case of native builds we don't do it because we want to actually integrate with system libc. So we're stuck figuring out what the various systems want from us.

ifreund · 2022-05-13T22:16:24Z

On my glibc 2.32 void linux system /usr/lib/libc.so appears to be a linker script which pulls in libc_nonshared.a:

/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /usr/lib64/libc.so.6 /usr/lib64/libc_nonshared.a  AS_NEEDED ( /usr/lib64/ld-linux-x86-64.so.2 ) )

This might help explain things, in particular why I wasn't seeing any reference to libc_nonshared.a in gcc -v output on my system.

BratishkaErik · 2022-05-14T08:17:24Z

Ok, on my glibc 2.35 gentoo system cat /usr/lib/libc.so:

/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf32-i386)
GROUP ( /lib/libc.so.6 /usr/lib/libc_nonshared.a  AS_NEEDED ( /lib/ld-linux.so.2 ) )

cat /usr/lib64/libc.so:

/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /lib64/libc.so.6 /usr/lib64/libc_nonshared.a  AS_NEEDED ( /lib64/ld-linux-x86-64.so.2 ) )

matu3ba · 2022-05-15T07:27:16Z

On Arch its similar
cat /usr/lib/libc.so

/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /usr/lib/libc.so.6 /usr/lib/libc_nonshared.a  AS_NEEDED ( /usr/lib/ld-linux-x86-64.so.2 ) )

cat /usr/lib64/libc.so

/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /usr/lib/libc.so.6 /usr/lib/libc_nonshared.a  AS_NEEDED ( /usr/lib/ld-linux-x86-64.so.2 ) )

file /usr/lib/ld-linux.so.2 symlinking to /usr/lib32/ld-linux.so.2 should not make a difference in this context.

DONT INCLUDE THIS IN THE FINAL PR. This is just for convenience as I switch back and forth from my two laptops.

BratishkaErik · 2022-06-04T16:16:01Z

$ cat a.c
extern char __libc_single_threaded;
int main(void) {
    return __libc_single_threaded;
}
$ clang a.c
$ zig build-exe a.c -lc
ld.lld: error: undefined symbol: __libc_single_threaded
>>> referenced by a.c:3
>>>               /home/vexu/.cache/zig/o/00d791557252b46f5ed6668a930dc12a/a.o:(main)
error: LLDReportedFailure

Ah, and __libc_single_threaded was introduced in glibc 2.32

topolarity · 2022-07-17T22:15:03Z

On my system, Zig is in fact providing libc_nonshared.a, but the symbol is still missing:

$ ./zig-linux-x86_64-0.9.1/zig build-exe test.c -lc --verbose-link
ld.lld -error-limit=0 -O0 -z stack-size=16777216 --gc-sections -m elf_x86_64 -o test /home/topolarity/.cache/zig/o/3bb4baaa7fdbd4d420aa2c0ea0b25896/Scrt1.o /home/topolarity/.cache/zig/o/f01eecd9f532c366e29902dc433e6bbc/crti.o -dynamic-linker /lib64/ld-linux-x86-64.so.2 /home/topolarity/.cache/zig/o/4f097214eb5219ae4350051529af36b2/test.o /home/topolarity/.cache/zig/o/8e947370e0e9a95237b40481a6c38c41/libcompiler_rt.a --as-needed /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libm.so.6 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libpthread.so.0 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libc.so.6 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libdl.so.2 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/librt.so.1 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libld.so.2 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libutil.so.1 /home/topolarity/.cache/zig/o/fa5988d449df15a0a124339ef2635cc7/libc_nonshared.a /home/topolarity/.cache/zig/o/b569a0eace5a24dad59f9ea9da18f67d/crtn.o
ld.lld: error: undefined symbol: __libc_single_threaded
>>> referenced by test.c:3
>>>               /home/topolarity/.cache/zig/o/4f097214eb5219ae4350051529af36b2/test.o:(main)
error: LLDReportedFailure
$

If I request a system library so that Zig integrates with system libc, the example actually works:

$ ./zig-linux-x86_64-0.9.1/zig build-exe test.c -lc -lz --verbose-link
ld.lld -error-limit=0 -O0 -z stack-size=16777216 --gc-sections -m elf_x86_64 -o test /usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../lib/crt1.o /usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../lib/crti.o -rpath /lib64 -rpath /lib -rpath /usr/lib64 -rpath /usr/lib -L /usr/local/lib64 -L /usr/local/lib -L /usr/lib/x86_64-linux-gnu -L /lib64 -L /lib -L /usr/lib64 -L /usr/lib -L /lib/x86_64-linux-gnu -L /usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../lib -dynamic-linker /lib64/ld-linux-x86-64.so.2 /home/topolarity/.cache/zig/o/93bdf25300a52e9361dec6260fcb51e3/test.o /home/topolarity/.cache/zig/o/8e947370e0e9a95237b40481a6c38c41/libcompiler_rt.a --as-needed -lz -lm -lpthread -lc -ldl -lrt -lutil /usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../lib/crtn.o
$

BratishkaErik · 2022-07-27T18:40:30Z

On my system, Zig is in fact providing libc_nonshared.a, but the symbol is still missing:

$ ./zig-linux-x86_64-0.9.1/zig build-exe test.c -lc --verbose-link
ld.lld -error-limit=0 -O0 -z stack-size=16777216 --gc-sections -m elf_x86_64 -o test /home/topolarity/.cache/zig/o/3bb4baaa7fdbd4d420aa2c0ea0b25896/Scrt1.o /home/topolarity/.cache/zig/o/f01eecd9f532c366e29902dc433e6bbc/crti.o -dynamic-linker /lib64/ld-linux-x86-64.so.2 /home/topolarity/.cache/zig/o/4f097214eb5219ae4350051529af36b2/test.o /home/topolarity/.cache/zig/o/8e947370e0e9a95237b40481a6c38c41/libcompiler_rt.a --as-needed /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libm.so.6 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libpthread.so.0 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libc.so.6 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libdl.so.2 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/librt.so.1 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libld.so.2 /home/topolarity/.cache/zig/o/b61716bae4d350e69e284aa7d351fe5d/libutil.so.1 /home/topolarity/.cache/zig/o/fa5988d449df15a0a124339ef2635cc7/libc_nonshared.a /home/topolarity/.cache/zig/o/b569a0eace5a24dad59f9ea9da18f67d/crtn.o
ld.lld: error: undefined symbol: __libc_single_threaded
>>> referenced by test.c:3
>>>               /home/topolarity/.cache/zig/o/4f097214eb5219ae4350051529af36b2/test.o:(main)
error: LLDReportedFailure
$

If I request a system library so that Zig integrates with system libc, the example actually works:

$ ./zig-linux-x86_64-0.9.1/zig build-exe test.c -lc -lz --verbose-link
ld.lld -error-limit=0 -O0 -z stack-size=16777216 --gc-sections -m elf_x86_64 -o test /usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../lib/crt1.o /usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../lib/crti.o -rpath /lib64 -rpath /lib -rpath /usr/lib64 -rpath /usr/lib -L /usr/local/lib64 -L /usr/local/lib -L /usr/lib/x86_64-linux-gnu -L /lib64 -L /lib -L /usr/lib64 -L /usr/lib -L /lib/x86_64-linux-gnu -L /usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../lib -dynamic-linker /lib64/ld-linux-x86-64.so.2 /home/topolarity/.cache/zig/o/93bdf25300a52e9361dec6260fcb51e3/test.o /home/topolarity/.cache/zig/o/8e947370e0e9a95237b40481a6c38c41/libcompiler_rt.a --as-needed -lz -lm -lpthread -lc -ldl -lrt -lutil /usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../lib/crtn.o
$

Can you please share output of ./zig-linux-x86_64-0.9.1/zig build-exe --show-builtin?

BratishkaErik · 2022-07-27T18:46:57Z

On my glibc 2.32 void linux system /usr/lib/libc.so appears to be a linker script which pulls in libc_nonshared.a:
/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /usr/lib64/libc.so.6 /usr/lib64/libc_nonshared.a  AS_NEEDED ( /usr/lib64/ld-linux-x86-64.so.2 ) )
This might help explain things, in particular why I wasn't seeing any reference to libc_nonshared.a in gcc -v output on my system.

I guess this will be fixed when #6469 will be fixed:

./zig targets | jq .native.triple: "x86_64-linux.5.18.14...5.18.14-gnu.2.19"
ldd --version: ldd (Gentoo 2.35-r8 p9) 2.35
./zig build-exe a.c -lc:

LLD Link... ld.lld: error: undefined symbol: __libc_single_threaded
>>> referenced by a.c:3 (/home/bratishkaerik/zig/build/a.c:3)
>>>               /home/bratishkaerik/.cache/zig/o/ba6cf5a0f60a803a3277d1158d1d817f/a.o:(main)

./zig build-exe a.c -lc -target x86_64-linux.5.18.14...5.18.14-gnu.2.32 (and higher, like 2.34): no error
./zig build-exe a.c -lc -target x86_64-linux.5.18.14...5.18.14-gnu.2.35:

error: zig does not yet provide glibc version 2.35, the max provided version is 2.34
error: unable to build glibc shared objects: InvalidTargetGLibCVersion

topolarity · 2022-07-27T19:30:38Z

Can you please share output of ./zig-linux-x86_64-0.9.1/zig build-exe --show-builtin?

Indeed, the wrong version of glibc is detected:

pub const os = std.Target.Os{
    .tag = .linux,
    .version_range = .{ .linux = .{
        .range = .{
            .min = .{
                .major = 5,
                .minor = 10,
                .patch = 102,
            },
            .max = .{
                .major = 5,
                .minor = 10,
                .patch = 102,
            },
        },
        .glibc = .{
            .major = 2,
            .minor = 19,
            .patch = 0,
        },
    }},
};

nektro · 2022-07-27T22:36:57Z

that's tracked separately in 6469

Previously, this code would fail to detect glibc version because it relied on libc.so.6 being a symlink which revealed the answer. On modern distros, this is no longer the case. This new strategy finds the path to libc.so.6 from /usr/bin/env, then inspects the .dynstr section of libc.so.6, looking for symbols that start with "GLIBC_2.". It then parses those as semantic versions and takes the maximum value as the system-native glibc version. closes #6469 see #11137 closes #12567

andrewrk · 2022-09-09T01:51:40Z

Could I get someone affected by this issue to check whether #12788 solves it?

Previously, this code would fail to detect glibc version because it relied on libc.so.6 being a symlink which revealed the answer. On modern distros, this is no longer the case. This new strategy finds the path to libc.so.6 from /usr/bin/env, then inspects the .dynstr section of libc.so.6, looking for symbols that start with "GLIBC_2.". It then parses those as semantic versions and takes the maximum value as the system-native glibc version. closes #6469 see #11137 closes #12567

Vexu · 2022-09-09T16:34:58Z

Duplicate of #6469 since the example works as expected with -target native-native-gnu.2.34.

Vexu added the frontend Tokenization, parsing, AstGen, Sema, and Liveness. label Mar 12, 2022

Vexu added this to the 0.10.0 milestone Mar 12, 2022

andrewrk added bug Observed behavior contradicts documented or intended behavior os-linux labels Mar 13, 2022

mewmew added a commit to mewpull/zig that referenced this issue Apr 26, 2022

stage2: fix build on Arch Linux

391a623

Prior to this commit, building on Arch Linux would result in the following linker error: undefined symbol: __libc_single_threaded Updates ziglang#11137.

mewmew mentioned this issue Apr 26, 2022

stage2: fix build on Arch Linux #11529

Closed

perillo mentioned this issue May 8, 2022

Update zig up to commit 496eb6927 CI: add non-LLVM backends to the test matrix ziglang/zig-bootstrap#84

Closed

BratishkaErik mentioned this issue May 31, 2022

stage2: fix building on systems with glibc >= 2.28 #11740

Closed

Techcable added a commit to Techcable/zig that referenced this issue Jun 2, 2022

[DONT PULL] Workaround for ziglang#11137

36dbc15

DONT INCLUDE THIS IN THE FINAL PR. This is just for convenience as I switch back and forth from my two laptops.

BratishkaErik mentioned this issue Jun 15, 2022

link c_nonshared #11865

Closed

xxxbxxx added a commit to xxxbxxx/zig that referenced this issue Jul 13, 2022

build stage2 cf ziglang#11137

a40da67

BratishkaErik mentioned this issue Jul 17, 2022

CMake: Improve usage of llvm-config (esp. for consistent static/shared linking) #12136

Merged

BratishkaErik mentioned this issue Aug 22, 2022

std.zig.system.NativeTargetInfo: use getconf for detecting glibc version on glibc systems #12567

Closed

andrewrk mentioned this issue Sep 9, 2022

std.zig.system.NativeTargetInfo: improve glibc version and dynamic linker detection #12788

Merged

Vexu closed this as completed Sep 9, 2022

BratishkaErik mentioned this issue Sep 9, 2022

zig cannot build against a native glibc greater than the latest cross-compilation-supported version of glibc #12797

Closed

bradlarsen mentioned this issue Jun 9, 2023

Support older versions of Linux with prebuilt release binaries praetorian-inc/noseyparker#58

Closed

rootbeer mentioned this issue Oct 14, 2023

errno seemingly lost during fstatat when -target with -gnu is specified #17034

Closed

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`-lc` doesn't link `c_nonshared` #11137

`-lc` doesn't link `c_nonshared` #11137

Vexu commented Mar 12, 2022

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nektro commented Jul 27, 2022

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Vexu commented Sep 9, 2022

-lc doesn't link c_nonshared #11137

-lc doesn't link c_nonshared #11137

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`-lc` doesn't link `c_nonshared` #11137

`-lc` doesn't link `c_nonshared` #11137

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