Decouple CodeGen from ErrorCode

Decouple CodeGen from ErrorCode

CodeGen's only dependency on ErrorCode was one MakeInstruction()
overload, which can be removed by making the caller responsible for
converting the ErrorCode to a BPF_RET'able value. Fortunately, there
are only two uses of this function:

1. SandboxBPF::RetExpression() which is easily fixed by simply calling
ErrorCode::err() to get the ErrorCode's error value.

2. codegen_unittest.cc which is merely testing the BPF code generator,
and so any return values will do: no need to be seccomp-bpf return
values... so just replace them with simple integer values.  (While
here, change a few bare "BPF_RET" arguments to "BPF_RET + BPF_K" just
to be consistent.)

After this CL, CodeGen focuses solely on assembling programs for the
abstract BPF machine, while higher-level abstractions (primarily
SandboxBPF) are responsible for using it in a way that's semantically
meaningful for seccomp-bpf.

BUG=414363
Committed: https://crrev.com/a5f2064030a34e71157085175b7ae93242509173
Cr-Commit-Position: refs/heads/master@{#295192}

[mdempsky, 2014-09-16 06:54:39]

mdempsky@chromium.org changed reviewers:
+ jln@chromium.org, rickyz@chromium.org

[mdempsky, 2014-09-16 06:54:40]

(Similar to https://codereview.chromium.org/572753002/, but decoupling CodeGen
instead of Trap now.)

[rickyz (no longer on Chrome), 2014-09-16 22:36:13]

On 2014/09/16 06:54:40, mdempsky wrote:
> (Similar to https://codereview.chromium.org/572753002/, but decoupling CodeGen
> instead of Trap now.)

LGTM

[rickyz (no longer on Chrome), 2014-09-16 22:36:46]

lgtm

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/sa...
File sandbox/linux/seccomp-bpf/sandbox_bpf.cc (right):

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/sa...
sandbox/linux/seccomp-bpf/sandbox_bpf.cc:891: return CondExpression(gen, err);
nit: fix indent

[rickyz (no longer on Chrome), 2014-09-16 22:36:49]

lgtm

[mdempsky, 2014-09-16 22:41:31]

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/sa...
File sandbox/linux/seccomp-bpf/sandbox_bpf.cc (right):

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/sa...
sandbox/linux/seccomp-bpf/sandbox_bpf.cc:891: return CondExpression(gen, err);
On 2014/09/16 22:36:46, rickyz wrote:
> nit: fix indent

Oops, done.

[jln (very slow on Chromium), 2014-09-16 22:42:29]

lgtm

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/sa...
File sandbox/linux/seccomp-bpf/sandbox_bpf.cc (right):

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/sa...
sandbox/linux/seccomp-bpf/sandbox_bpf.cc:896: SANDBOX_DIE("ErrorCode is not
suitable for returning from a BPF program");
Will this work with all compilers? I think there are cases where this is not
considered noreturn, so you may need to return NULL here.

[rickyz (no longer on Chrome), 2014-09-16 22:44:11]

Sorry for the spam, still figuring out how to use this thing :-)

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/co...
File sandbox/linux/seccomp-bpf/codegen.h (right):

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/co...
sandbox/linux/seccomp-bpf/codegen.h:46: //    
gen.MakeInstruction(BPF_RET+BPF_K, ErrorCode(ErrorCode::ERR_ALLOWED)));
This is a little out of date now (though feel free to ignore as well, since the
change to remove JoinInstructions will get rid of this line).

[mdempsky, 2014-09-16 22:47:44]

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/co...
File sandbox/linux/seccomp-bpf/codegen.h (right):

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/co...
sandbox/linux/seccomp-bpf/codegen.h:46: //    
gen.MakeInstruction(BPF_RET+BPF_K, ErrorCode(ErrorCode::ERR_ALLOWED)));
On 2014/09/16 22:44:10, rickyz wrote:
> This is a little out of date now (though feel free to ignore as well, since
the
> change to remove JoinInstructions will get rid of this line).

Yep, fixed in patch set 3. :)

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/sa...
File sandbox/linux/seccomp-bpf/sandbox_bpf.cc (right):

https://codereview.chromium.org/576673003/diff/1/sandbox/linux/seccomp-bpf/sa...
sandbox/linux/seccomp-bpf/sandbox_bpf.cc:896: SANDBOX_DIE("ErrorCode is not
suitable for returning from a BPF program");
On 2014/09/16 22:42:29, jln wrote:
> Will this work with all compilers?

I think so.  There are other functions in this file (e.g., BPFFailure) that call
SANDBOX_DIE() and don't have any return statements.

[mdempsky, 2014-09-16 23:05:19]

The CQ bit was checked by mdempsky@chromium.org

[commit-bot: I haz the power, 2014-09-16 23:07:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/576673003/40001

[commit-bot: I haz the power, 2014-09-17 00:46:11]

Committed patchset #3 (id:40001) as 91dd7a2bf7b21749675770fcd97cbcc02253ca18

[commit-bot: I haz the power, 2014-09-17 00:47:02]

Patchset 3 (id:??) landed as
https://crrev.com/a5f2064030a34e71157085175b7ae93242509173
Cr-Commit-Position: refs/heads/master@{#295192}