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X-Proofpoint-Spam-Info: AW1haW4tMjYwOTI0MDA2NiBTYWx0ZWRfX/bepRdgQpOsA xWKjLfYxbWbF4TY1O98/E/zTq2XLw85xvtdL2Cbt3c8Y6yvfpS4l5UwsK+036o4zrsk21+jc2S2 gZ17DfuytRe8BUSNYP9pe1bxDepVHtwF2+QtQJe8gh/9lpuCQMKF On 17/09/2026 17:40, Yonghong Song wrote: > > The arm64 ABI starts an argument twice the register size on an even-numbered > argument register, leaving a hole when the next free register is an odd one: > > u64 f(u64 a, __int128 v, u64 b); > > passes a in x0, v in x2:x3 -- skipping x1 -- and b in x4. pahole did not > model the hole, so b looked like it was in an unexpected register and the > whole function was dropped from BTF. Patch 1 skips the register the ABI > leaves behind, patch 3 adds a test for it. Only arm64 has this rule; the > other architectures are unaffected. > > Patch 2 is a small follow-up. Floating point and vector arguments are > allocated from a register bank of their own -- v0-v7 on arm64, xmm0-xmm7 on > x86-64 -- so a wide one never occupies a general purpose register pair and > must not trigger the even-register rule either. It does not change the BTF > emitted today, because such an argument still advances the general purpose > register index by its own size, so it comes with no test of its own; it > keeps the alignment rule scoped to the bank it applies to. > one small issue here; we record alignment for structs from DW_AT_align in associated tags; we should ensure that we utilize that alignment where available. However it's a bit broken in that we don't appear to record alignment for typedefs, just structs. I think we can tackle that with a followup though; unless anyone objects I'll land these patches later today. > Changelog: > v1 -> v2: > - v1: https://lore.kernel.org/bpf/20260911040955.339939-1-yonghong.song@linux.dev/ > - add commit "Do not align the argument register index for FP arguments". > > Yonghong Song (3): > dwarf_loader: Skip the argument register the arm64 ABI leaves as a > hole > dwarf_loader: Do not align the argument register index for FP > arguments > tests: tests: Add test for 16-byte aligned arguments on arm64 > > dwarf_loader.c | 72 ++++++++++++++++++++++++++++++++-- > dwarves.h | 11 ++++++ > tests/clang_parm_align16.sh | 77 +++++++++++++++++++++++++++++++++++++ > tests/test_lib.sh | 3 +- > 4 files changed, 158 insertions(+), 5 deletions(-) > create mode 100755 tests/clang_parm_align16.sh > > -- > 2.53.0-Meta >