From b8a64b8ec9cd3d8f6e3f23e44312c4903eccac45 Mon Sep 17 00:00:00 2001 From: Clemens Fruhwirth Date: Wed, 12 Sep 2007 09:44:30 +0000 Subject: [PATCH] Sign extension hack to work around PC64 relocation limitation for binutils <2.17 for x86_64. binutils <2.17 can't generate PC64 relocations for x86_64. Hence we emit only 32 bit PC relative offsets, and artifically stick a zero in front of them to make them 64 bit (see PprMach.sh ppr_item in pprDataItem). This works as long as the offset is <32bit AND it's positive. This is not the case for offsets in jump tables, they are all negative. This hack sign extends them with a MOVSXL instruction into the dead index register, then adding the properly sign extended offset to the jump table base label giving the correct target address for the following jump. --- compiler/nativeGen/MachCodeGen.hs | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/compiler/nativeGen/MachCodeGen.hs b/compiler/nativeGen/MachCodeGen.hs index 65300a7..081d3ef 100644 --- a/compiler/nativeGen/MachCodeGen.hs +++ b/compiler/nativeGen/MachCodeGen.hs @@ -3896,7 +3896,8 @@ genSwitch expr ids op = OpAddr (AddrBaseIndex (EABaseReg tableReg) (EAIndex reg wORD_SIZE) (ImmInt 0)) -#if x86_64_TARGET_ARCH && darwin_TARGET_OS +#if x86_64_TARGET_ARCH +#if darwin_TARGET_OS -- on Mac OS X/x86_64, put the jump table in the text section -- to work around a limitation of the linker. -- ld64 is unable to handle the relocations for @@ -3909,6 +3910,23 @@ genSwitch expr ids LDATA Text (CmmDataLabel lbl : jumpTable) ] #else + -- HACK: On x86_64 binutils<2.17 is only able to generate PC32 + -- relocations, hence we only get 32-bit offsets in the jump + -- table. As these offsets are always negative we need to properly + -- sign extend them to 64-bit. This hack should be removed in + -- conjunction with the hack in PprMach.hs/pprDataItem once + -- binutils 2.17 is standard. + code = e_code `appOL` t_code `appOL` toOL [ + LDATA ReadOnlyData (CmmDataLabel lbl : jumpTable), + MOVSxL I32 + (OpAddr (AddrBaseIndex (EABaseReg tableReg) + (EAIndex reg wORD_SIZE) (ImmInt 0))) + (OpReg reg), + ADD wordRep (OpReg reg) (OpReg tableReg), + JMP_TBL (OpReg tableReg) [ id | Just id <- ids ] + ] +#endif +#else code = e_code `appOL` t_code `appOL` toOL [ LDATA ReadOnlyData (CmmDataLabel lbl : jumpTable), ADD wordRep op (OpReg tableReg), -- 1.7.10.4