From d6ab9c60288369ec991826b158d751dd4cb3319e Mon Sep 17 00:00:00 2001 From: Moritz Angermann Date: Tue, 22 Jun 2021 15:39:44 +0800 Subject: [aarch64-macho] Fix off-by-one error in the linker We need to be careful about the sign bit for BR26 relocation otherwise we end up encoding a large positive number and reading back a large negative number. --- rts/linker/MachO.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'rts/linker') diff --git a/rts/linker/MachO.c b/rts/linker/MachO.c index cdafcb1c89..1a18ee6a74 100644 --- a/rts/linker/MachO.c +++ b/rts/linker/MachO.c @@ -551,7 +551,17 @@ relocateSectionAarch64(ObjectCode * oc, Section * section) } else { value = (uint64_t)symbol->addr; // address of the symbol. } - if((value - pc + addend) >> (2 + 26)) { + // We've got: + // + 2 bits, for alignment + // + 26 bits for for the relocation value + // - 1 bit for signage. + // + // Thus we can encode 26 bits for relocation, including the sign + // bit. However as branches need to be 4-byte aligned, we only + // need 26 bits to address a 28 bit range. Thus discarding the + // sign bit, we can encode a range of +/- 27bits. + // + if((value - pc + addend) >> (2 + 26 - 1)) { /* we need a stub */ /* check if we already have that stub */ if(findStub(section, (void**)&value, 0)) { -- cgit v1.2.1