aokblast wrote:
> > In clang-repl, R_*_32 relocations are emitted as direct 32-bit PC-relative
> > references. A normal static linker can resolve references to distinct
> > symbol through the GOT or Copy relocation, but clang-repl directly mmaps
> > shared objects into memory and bypasses the static linker.
>
> Can you be more specific about the relocations that you're seeing?
>
> CodeGen usually requests a GOT entry (by selecting one of the GOT relocations
> and producing the necessary instruction sequence), and the linker just builds
> the requested GOT entry.
>
> The usual caveat is hidden symbols:
>
> ```c
> extern int __attribute__((visibility("hidden"))) X;
> int getX() { return X; } // <- will typically emit 32-bit PC-relative
> reference
> ```
>
> The problem in this case is that ClangRepl probably isn't doing slab
> allocation by default, in which case switching to a slab-based allocator is
> the best answer.
GOT is only generated for relocatable code when -fPIC is enabled. This is not
the default in ClangRepl. I previously tried building relocatable objects in
ClangRepl with -fPIC, but encountered a test failure.
The issue is that ClangRepl can consume PCH (precompiled headers) where the
headers are compiled normally (i.e., without -fPIC). This leads to a mismatch
in PIC levels between objects, causing assertion failures.
I can share the failing test case that triggered this patch on FreeBSD.
Here is my experiment:
```
blast@linux-dev ~/p/cpp> cvat ^C
blast@linux-dev ~/p/cpp> cat test.cpp
extern int X;
int getX() { return X; }
blast@linux-dev ~/p/cpp> cc test.cpp -c -o test.o
blast@linux-dev ~/p/cpp> readelf --relocs test.o
Relocation section '.rela.text' at offset 0x168 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
00000000000a 000400000002 R_X86_64_PC32 0000000000000000 X - 4
Relocation section '.rela.eh_frame' at offset 0x180 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
000000000020 000200000002 R_X86_64_PC32 0000000000000000 .text + 0
blast@linux-dev ~/p/cpp> cc -fPIC test.cpp -c -o test.o
blast@linux-dev ~/p/cpp> readelf --relocs test.o
Relocation section '.rela.text' at offset 0x1a0 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
00000000000b 00050000002a R_X86_64_REX_GOTP 0000000000000000 X - 4
Relocation section '.rela.eh_frame' at offset 0x1b8 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
000000000020 000200000002 R_X86_64_PC32 0000000000000000 .text + 0
blast@linux-dev ~/p/cpp> uname -a
Linux linux-dev 6.8.12-13-pve #1 SMP PREEMPT_DYNAMIC PMX 6.8.12-13
(2025-07-22T10:00Z) x86_64 x86_64 x86_64 GNU/Linux
```
https://github.com/llvm/llvm-project/pull/201286
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