<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/102490>102490</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
[lld] ld.lld should allow explicitly setting a target (ignore other objects and linker scripts for other targets)
</td>
</tr>
<tr>
<th>Labels</th>
<td>
lld
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
chitao1234
</td>
</tr>
</table>
<pre>
# Brief
When cross compiling, ld.lld `-m` option overwritten by host machine linker script, binutils ld handle this situation correctly.
# Detailed problem explanation
In a Linux system using glibc, `/lib/libc.so` is a linker script that sets `OUTPUT_FORMAT` to the host machine.
Example 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 ) )
```
When cross compiling using clang and lld, if set `-L` option incorrectly, lld would search host library first and load the linker script, such that lld would fail with a weird error message.
```
% ld.lld --sysroot=/usr/aarch64-linux-gnu -EL --hash-style=gnu --build-id --eh-frame-hdr -m aarch64linux -pie -dynamic-linker /lib/ld-linux-aarch64.so.1 -o a.out /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/Scrt1.o /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/crti.o /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/crtbeginS.o -L/lib -L/usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0 -L/usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/../lib64 -L/usr/aarch64-linux-gnu/lib/../lib64 -L/usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib -L/usr/aarch64-linux-gnu/lib --verbose test.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/crtendS.o /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/crtn.o
ld.lld: set maximum concurrency to 16, specify --threads= to change
ld.lld: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/Scrt1.o
ld.lld: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/crti.o
ld.lld: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/crtbeginS.o
ld.lld: test.o
ld.lld: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a
ld.lld: /lib/libgcc_s.so
ld.lld: /lib/libgcc_s.so.1
ld.lld: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a
ld.lld: /lib/libc.so
ld.lld: /usr/lib/libc.so.6
ld.lld: /usr/lib/libc_nonshared.a
ld.lld: /usr/lib/ld-linux-x86-64.so.2
ld.lld: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a
ld.lld: /lib/libgcc_s.so
ld.lld: /lib/libgcc_s.so.1
ld.lld: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a
ld.lld: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/crtendS.o
ld.lld: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/crtn.o
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/Scrt1.o is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/crti.o is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/crtbeginS.o is incompatible with elf64-x86-64
ld.lld: error: test.o is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_1_1.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_2_1.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_4_1.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_8_1.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_16_1.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_1_2.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_2_2.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_4_2.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_8_2.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_16_2.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_1_3.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_2_3.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_4_3.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_8_3.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_16_3.o) is incompatible with elf64-x86-64
ld.lld: error: /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/libgcc.a(cas_1_4.o) is incompatible with elf64-x86-64
ld.lld: error: too many errors emitted, stopping now (use --error-limit=0 to see all errors)
```
It's worth noting that binutils ld handle this case correctly, due to it being single targeted.
binutils ld behavior:
```
% aarch64-linux-gnu-ld --sysroot=/usr/aarch64-linux-gnu -EL --hash-style=gnu --build-id --eh-frame-hdr -m aarch64linux -pie -dynamic-linker /lib/ld-linux-aarch64.so.1 -o a.out /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/Scrt1.o /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/crti.o /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/crtbeginS.o -L/lib -L/usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0 -L/usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/../lib64 -L/usr/aarch64-linux-gnu/lib/../lib64 -L/usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib -L/usr/aarch64-linux-gnu/lib test.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/crtendS.o /usr/bin/../lib64/gcc/aarch64-linux-gnu/14.1.0/../../../../aarch64-linux-gnu/lib/crtn.o
aarch64-linux-gnu-ld: skipping incompatible /lib/libgcc_s.so.1 when searching for libgcc_s.so.1
aarch64-linux-gnu-ld: skipping incompatible /lib/libgcc_s.so.1 when searching for libgcc_s.so.1
aarch64-linux-gnu-ld: skipping incompatible /lib/libc.so when searching for -lc
aarch64-linux-gnu-ld: skipping incompatible /lib/libc.a when searching for -lc
aarch64-linux-gnu-ld: skipping incompatible /lib/libgcc_s.so.1 when searching for libgcc_s.so.1
aarch64-linux-gnu-ld: skipping incompatible /lib/libgcc_s.so.1 when searching for libgcc_s.so.1
```
Currently in lld, `-m` option is used by clang to set target, `-m` sets the `config->emulation`, but linker script sets `config->bfdname`, lld would always prefer using `bfdname` as the target, casuing the aforementioned cryptic error message.
This situation is quite common unfortuantely, due to some build tool not handling cross compilation well enough (like `libtool`). It would be nice for lld to behave the same as binutils ld in this situation, both for compatibility and robustness.
# Additional infomation:
## Versions:
```
LLD 18.1.8 (compatible with GNU linkers)
clang version 18.1.8
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
GNU ld (GNU Binutils) 2.42.0
Copyright (C) 2024 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later version.
This program has absolutely no warranty.
```
Linux distro: EndeavourOS
# Steps for reproducing:
```shell
# linker error
echo 'int main(){}' | clang -target aarch64-linux-gnu -xc --sysroot=/usr/aarch64-linux-gnu -L/lib -fuse-ld=lld -
# no error
echo 'int main(){}' | clang -target aarch64-linux-gnu -xc --sysroot=/usr/aarch64-linux-gnu -L/lib -
```
</pre>
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