https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?id=4783a4ddd4740d948fb987ed8a7cf2932d5ad5c4 From 4783a4ddd4740d948fb987ed8a7cf2932d5ad5c4 Mon Sep 17 00:00:00 2001 From: Yao Zi Date: Sat, 13 Dec 2025 08:27:22 +0000 Subject: dwarf_loader: Handle DW_AT_location attrs containing DW_OP_plus_uconst LLVM has a GlobalMerge pass, which tries to group multiple global variables together and address them with through a single register with offsets coded in instructions, to reduce register pressure. Address of symbols transformed by the pass may be represented by an DWARF expression consisting of DW_OP_addrx and DW_OP_plus_uconst, which naturally matches the way a merged variable is addressed. However, our dwarf_loader currently ignores anything but the first in the location expression, including the DW_OP_plus_uconst atom, which appears the second operation in this case. This could result in broken BTF information produced by pahole, where several merged symbols are given the same offset, even though in fact they don't overlap. LLVM has enabled MergeGlobal pass for PowerPC[1] and RISC-V[2] by default since version 20, let's handle DW_OP_plus_uconst operations in DW_AT_location attributes correctly to ensure correct BTF could be produced for LLVM-built kernels. Fixes: a6ea527aab91 ("variable: Add ->addr member") Reported-by: q66 Closes: https://github.com/ClangBuiltLinux/linux/issues/2089 Link: https://github.com/llvm/llvm-project/commit/aaa37d6755e6 # [1] Link: https://github.com/llvm/llvm-project/commit/9d02264b03ea # [2] Link: https://lore.kernel.org/dwarves/20251213082721.51017-2-me@ziyao.cc/ Signed-off-by: Yao Zi Acked-by: Yonghong Song Signed-off-by: Alan Maguire --- dwarf_loader.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/dwarf_loader.c b/dwarf_loader.c index 79be3f5..77aab8a 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -708,6 +708,11 @@ static enum vscope dwarf__location(Dwarf_Die *die, uint64_t *addr, struct locati case DW_OP_addrx: scope = VSCOPE_GLOBAL; *addr = expr[0].number; + + if (location->exprlen == 2 && + expr[1].atom == DW_OP_plus_uconst) + *addr += expr[1].number; + break; case DW_OP_reg1 ... DW_OP_reg31: case DW_OP_breg0 ... DW_OP_breg31: -- cgit 1.3-korg