Remove Hack in compiler/nativeGen/X86/CodeGen.hs

Remove the hack around Line 3914 labeled with:

    -- 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.

This bug is intended for house keeping.

changed weight to 5

added NCG backend Tbug Trac import labels

changed the description

changed milestone to %6.12 branch

changed milestone to %6.12.3

removed milestone

changed weight to 3

Trac metadata

Trac field	Value
Priority	normal → low

changed milestone to %7.0.2

changed milestone to %7.2.1

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TypeOfFailure	- → OtherFailure

changed milestone to %7.4.1

changed milestone to %7.6.1

changed weight to 0

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Priority	low → lowest

changed milestone to %7.6.2

changed milestone to %7.8.1

changed weight to 7

This was opened 4 years ago; let's see if we can remove the hack and close it now.

nb, it's now in nativeGen/X86/CodeGen.hs.

Trac metadata

Trac field	Value
Priority	lowest → high

assigned to @trac-thoughtpolice and unassigned @trac-clemens

changed milestone to %7.10.1

changed weight to 5

Trac metadata

Trac field	Value
Priority	high → normal

added 1 deleted label

removed milestone

Moving to 7.12.1 milestone; if you feel this is an error and should be addressed sooner, please move it back to the 7.10.1 milestone.

Attached file test-64bit-pc-rel-reloc.sh (download).

Test for 64 bit pc-relative relocations

I have just (2015/03/03) written a shell script (attached) that tests for binutils support for 64 bit pc-relative relocatons. The test passes on *all* modern linux systems, but fails on Mac OSX (Mavericks) and OpenBSD 5.5 (current is 5.6). The failure is one OpenBSD says:

linkasm.s:3: Error: can not do 8 byte pc-relative relocation

OpenBSD has GNU binutils 2.15 but they are unlikely to upgrade to a later version because later versions are under GPLv3 instead of GPLv2. However, they may at some stage switch to some other linker.

OSX has the linker from LLVM which theoretically could be fixed.

Trac metadata

Trac field	Value
CC	dterei, simonmar → dterei, erikd, simonmar

changed title from Remove Hack in compiler/nativeGen/MachCodeGen.hs to Remove Hack in compiler/nativeGen/X86/CodeGen.hs

I would not be surprised if it was better (equal or faster performance and smaller object file size) to use 32-bit offsets anyways, has anyone done a performance test?

changed weight to 3

As austin writes in D694, we are not going to able to change that in the near future anyways. Lowering severity.

Trac metadata

Trac field	Value
Priority	normal → low

Oh, I see the jump table entries are currently padded to 64 bits anyways. So then it should be slightly better to use a 64-bit relocation instead, but maybe it would be even better to pack the entries into 32 bits instead.

From D694: "If there still are broken binutils around, then maybe we should simply leave the current code (which works) in for another 10 years."

Trac metadata

Trac field	Value
Type	Bug → Task

changed milestone to %8.0.1

Milestone renamed

changed milestone to %8.2.1

This isn't happening any time soon.

mentioned in issue #11758 (closed)

See also #11758 (closed), where a failed attempt was made to delete the hack.

changed milestone to %8.4.1

Given that 8.2.1-rc1 is imminent, I'm bumping these off to the 8.4

mentioned in issue #13849 (closed)

changed milestone to %8.6.1

I tried to remove this hack again but the affected linker versions are still too prevalent. I suspect we'll have to wait a few more years for this.

changed milestone to %8.8.1

We won't be don't this in 8.6.