code review 132000043: debug/elf: support arm64 relocations

debug/elf: support arm64 relocations

This adds the minimal support for AArch64/arm64 relocations
needed to get cgo to work (when an isomorphic patch is applied
to gccgo) and a test.

This change uses the "AAarch64" name for the architecture rather
than the more widely accepted "arm64" because that's the name that
the relevant docs from ARM such as

   http://infocenter.arm.com/help/topic/com.arm.doc.ihi0056b/IHI0056B_aaelf64.pdf

all use.

Fixes issue 8533.

[mwhudson, 2014-08-21 09:37:45]

Hello golang-codereviews@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go/

[aram, 2014-08-21 09:44:35]

FWIW, the GOOS for the WIP Go on arm64 target is arm64.

[aram, 2014-08-21 09:53:11]

> FWIW, the GOOS for the WIP Go on arm64 target is arm64.

I meant GOARCH, obviously. And I was just mentioning some trivia, the name of
the constants should match the doc, e.g. we use R_X86_64_GLOB_DAT even though
out GOARCH is amd64. We should change the function names, though.

[gobot, 2014-08-21 09:54:40]

R=iant@golang.org (assigned by aram@mgk.ro)

[mwhudson, 2014-08-21 11:03:31]

On 2014/08/21 09:53:11, aram wrote:
> > FWIW, the GOOS for the WIP Go on arm64 target is arm64.
> 
> I meant GOARCH, obviously. And I was just mentioning some trivia, the name of
> the constants should match the doc, e.g. we use R_X86_64_GLOB_DAT even though
> out GOARCH is amd64. We should change the function names, though.

I changed the function name to applyRelocationsARM64.

[minux, 2014-08-21 14:54:00]

while you're here, why not add the full set of relocation values?

[mwhudson, 2014-08-21 20:26:44]

On 2014/08/21 14:54:00, minux wrote:
> while you're here, why not add the full set of relocation values?

OK, I've added all the relocations binutils knows about (via the power of
awk...).

[minux, 2014-08-22 15:11:55]

https://codereview.appspot.com/132000043/diff/120001/src/pkg/debug/elf/elf.go
File src/pkg/debug/elf/elf.go (right):

https://codereview.appspot.com/132000043/diff/120001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:14: * "ELF for the ARM® 64-bit Architecture (AArch64)"
(ARM IHI 0056B)
what's the copyright status? is it public domain?
do we need to add something below.

https://codereview.appspot.com/132000043/diff/120001/src/pkg/debug/elf/file.go
File src/pkg/debug/elf/file.go (right):

https://codereview.appspot.com/132000043/diff/120001/src/pkg/debug/elf/file.g...
src/pkg/debug/elf/file.go:533: return f.applyRelocationsAARCH64(dst, rels)
s/AARCH64/ARM64/

[mwhudson, 2014-08-25 01:48:07]

ptal

https://codereview.appspot.com/132000043/diff/120001/src/pkg/debug/elf/elf.go
File src/pkg/debug/elf/elf.go (right):

https://codereview.appspot.com/132000043/diff/120001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:14: * "ELF for the ARM® 64-bit Architecture (AArch64)"
(ARM IHI 0056B)
On 2014/08/22 15:11:54, minux wrote:
> what's the copyright status? is it public domain?

No, of course not, this is ARM we're talking about :)

> do we need to add something below.

I don't know, the document is here:
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0056b/IHI0056B_aaelf64.pdf

To be fair, in this revision the numbers are more derived from GNU binutils than
the ARM documentation... I could also "derive" them from LLVM if that would be
easier from a copyright/licensing POV (although clearly this is all derived from
the same place i.e. ARM Holdings plc)

https://codereview.appspot.com/132000043/diff/120001/src/pkg/debug/elf/file.go
File src/pkg/debug/elf/file.go (right):

https://codereview.appspot.com/132000043/diff/120001/src/pkg/debug/elf/file.g...
src/pkg/debug/elf/file.go:533: return f.applyRelocationsAARCH64(dst, rels)
On 2014/08/22 15:11:54, minux wrote:
> s/AARCH64/ARM64/

Done.

[iant, 2014-08-25 02:26:03]

Trivial nit: the first line of the CL description should be

debug/elf: support arm64 relocations

(lower case "support", arm64 rather than AArch64).

[iant, 2014-08-25 02:42:45]

It's fine with me if you split out the change adding the reloc numbers to
debug/elf/elf.go.

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go
File src/pkg/debug/elf/elf.go (right):

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:784: R_AARCH64_P32_ABS32                      
R_AARCH64 = 1
Do any of these values less than 256 actually appear in Aarch64 ELF files?  I
assume you got these from the GNU binutils but they are not in the Aarch64 ELF
spec
(http://infocenter.arm.com/help/topic/com.arm.doc.ihi0056b/IHI0056B_aaelf64.pdf).

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:834: R_AARCH64_NULL                           
R_AARCH64 = 256
I guess R_AARCH64_NULL is OK.  The spec shows it as withdrawn but also says it
should be treated as R_AARCH64_NONE.

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:864: R_AARCH64_LDST128_ABS_LO12_NC            
R_AARCH64 = 299
The spec does have reloc types for 287 through 293 and 300 through 308, and 310
and 313.

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:868: R_AARCH64_TLSGD_ADR_PAGE21               
R_AARCH64 = 513
512 is R_AARCH64_TLSGD_ADR_PREL21.

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:870: R_AARCH64_TLSIE_MOVW_GOTTPREL_G1         
R_AARCH64 = 539
Ths spec defines 515 through 538.

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:892: R_AARCH64_TLSDESC_CALL                   
R_AARCH64 = 569
570 and 571 are defined.

[mwhudson, 2014-08-25 03:38:45]

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go
File src/pkg/debug/elf/elf.go (right):

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:784: R_AARCH64_P32_ABS32                      
R_AARCH64 = 1
On 2014/08/25 02:42:44, iant wrote:
> Do any of these values less than 256 actually appear in Aarch64 ELF files?  I
> assume you got these from the GNU binutils but they are not in the Aarch64 ELF
> spec
>
(http://infocenter.arm.com/help/topic/com.arm.doc.ihi0056b/IHI0056B_aaelf64.pdf).

Ah, hm.  I indeed got them from GNU binutils.  They are the relocation codes for
the (still not completely formalized I think, but in practice defined) "ilp32"
model, where the AArch64 instructions are used with 32-bit pointers (so like
http://en.wikipedia.org/wiki/X32_ABI in the intel world).    There is a beta
specification here: 

http://infocenter.arm.com/help/topic/com.arm.doc.ihi0056c/IHI0056C_beta_aaelf...

I suppose you can build yourself a ilp32-targeting gccgo, build cgo with that
and then try to _use_ that cgo, in which case you probably need to know about
these relocations (although, certainly, this patch is not sufficient in that
case).

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:864: R_AARCH64_LDST128_ABS_LO12_NC            
R_AARCH64 = 299
On 2014/08/25 02:42:44, iant wrote:
> The spec does have reloc types for 287 through 293 and 300 through 308, and
310
> and 313.

Your patience for reading specs clearly vastly outweighs mine.  Done.

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:868: R_AARCH64_TLSGD_ADR_PAGE21               
R_AARCH64 = 513
On 2014/08/25 02:42:44, iant wrote:
> 512 is R_AARCH64_TLSGD_ADR_PREL21.

Done.

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:870: R_AARCH64_TLSIE_MOVW_GOTTPREL_G1         
R_AARCH64 = 539
On 2014/08/25 02:42:44, iant wrote:
> Ths spec defines 515 through 538.

Done.

https://codereview.appspot.com/132000043/diff/140001/src/pkg/debug/elf/elf.go...
src/pkg/debug/elf/elf.go:892: R_AARCH64_TLSDESC_CALL                   
R_AARCH64 = 569
On 2014/08/25 02:42:44, iant wrote:
> 570 and 571 are defined.

Done.  (I've also added the missing ILP32 codes from the draft spec).

[iant, 2014-08-28 03:14:28]

LGTM

[iant, 2014-08-28 03:19:01]

*** Submitted as https://code.google.com/p/go/source/detail?r=50f9b7e05ec3 ***

debug/elf: support arm64 relocations

This adds the minimal support for AArch64/arm64 relocations
needed to get cgo to work (when an isomorphic patch is applied
to gccgo) and a test.

This change uses the "AAarch64" name for the architecture rather
than the more widely accepted "arm64" because that's the name that
the relevant docs from ARM such as

  
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0056b/IHI0056B_aaelf64.pdf

all use.

Fixes issue 8533.

LGTM=iant
R=golang-codereviews, aram, gobot, iant, minux
CC=golang-codereviews
https://codereview.appspot.com/132000043

Committer: Ian Lance Taylor <iant@golang.org>