[LLD] Empty .interp section in vmlinux breaks GDB debugging on PowerPC

[vishalc-ibm]

Environment

• Target: PowerPC
• Host: X86
• Build command: make LLVM=1 ARCH=powerpc -j $(nproc) vmlinux

Issue

LLD generates vmlinux with an empty .interp section, causing GDB to crash when connecting to QEMU:

gdb vmlinux
(gdb) target remote :1234  # crashes here

$ make LLVM=1 ARCH=powerpc  -j`nproc` vmlinux  # compiles fine
$ llvm-readelf -p .interp vmlinux
String dump of section '.interp':

Expected Behavior

The kernel should not have a .interp section. GNU ld does not emit this section:

$ make LLVM=1 ARCH=powerpc LD=powerpc64le-linux-gnu-ld -j 8 vmlinux  # compiles fine
$ llvm-readelf -p .interp vmlinux
llvm-readelf: warning: 'vmlinux': could not find section '.interp'

Impact

Breaks kernel debugging with QEMU+GDB for PowerPC builds using LLVM.

📌 GDB Bugzilla
📌 LKML Thread

[llvmbot]

@llvm/issue-subscribers-lld-elf

Author: None (vishalc-ibm)

## Environment - **Target**: PowerPC - **Host**: X86 - **Build command**: `make LLVM=1 ARCH=powerpc -j $(nproc) vmlinux`

Issue

LLD generates vmlinux with an empty .interp section, causing GDB to crash when connecting to QEMU:

gdb vmlinux
(gdb) target remote :1234  # crashes here

$ make LLVM=1 ARCH=powerpc  -j`nproc` vmlinux  # works fine
$ llvm-readelf -p .interp vmlinux
String dump of section '.interp':

Expected Behavior

The kernel should not have a .interp section. GNU ld does not emit this section:

$ make LLVM=1 ARCH=powerpc LD=powerpc64le-linux-gnu-ld -j 8 vmlinux  # works fine
$ llvm-readelf -p .interp vmlinux
llvm-readelf: warning: 'vmlinux': could not find section '.interp'

Impact

Breaks kernel debugging with QEMU+GDB for PowerPC builds using LLVM.

📌 GDB Bugzilla
📌 [LKML Thread](https://lore.kernel.org/all/20251013040148.560439-1-vishalc@linux.ibm.com/)

[MaskRay]

# llvm-project build
ninja -C /tmp/Rel clang lld llvm-{ar,nm,objcopy,objdump,ranlib,readelf,strings,strip}

# linux kernel
PATH=/tmp/Rel/bin:$PATH make LLVM=1 ARCH=powerpc  -j 40 defconfig vmlinux O=/tmp/linux/ppc

lld works as intended. vmlinux is linked -pie mode with a linker script.
The output section description (.interp : AT(ADDR(.interp) - LOAD_OFFSET) { *(.interp) }) involves ADDR(.interp) and lld does not discard the empty .interp.
The output section is empty, so GNU ld discards it, even if its address is referenced by ADDR(.interp). This isn't safe if ADDR(.interp) is used elsewhere. There are possibly other conditions whether this would not be safe. LLD implements a simple rule: retain the section if it is referenced by an ADDR/LOADADDR. I don't think implementing more complex GNU-ld like rules in lld is worthwhile.

Other architectures don't have .interp in their linker script. Suggested change to linux:

--- i/arch/powerpc/kernel/vmlinux.lds.S
+++ w/arch/powerpc/kernel/vmlinux.lds.S
@@ -330,7 +330,6 @@ SECTIONS
        }
        .hash : AT(ADDR(.hash) - LOAD_OFFSET) { *(.hash) }
        .gnu.hash : AT(ADDR(.gnu.hash) - LOAD_OFFSET) { *(.gnu.hash) }
-       .interp : AT(ADDR(.interp) - LOAD_OFFSET) { *(.interp) }
        .rela.dyn : AT(ADDR(.rela.dyn) - LOAD_OFFSET)
        {
                __rela_dyn_start = .;

[MaskRay]

Close as intended behavior. There is a pending patch that removes .interp : AT(ADDR(.interp) - LOAD_OFFSET) { *(.interp) } ClangBuiltLinux/linux#2137

[vishalc-ibm]

https://lore.kernel.org/all/20251018-ppc-fix-lld-interp-v1-1-a083de6dccc9@kernel.org/

Consider reviewing at this patch.