1439659 - MOZ_LITTLE_ENDIAN and MOZ_BIG_ENDIAN should be function-like macros

Status: RESOLVED FIXED

(Core :: MFBT, enhancement, P3)

Description

[Jason Orendorff [:jorendorff]]

We have a lot of code that does stuff like

    #if MOZ_LITTLE_ENDIAN
    ...
    #else
    ...
    #endif

without first doing #include "mozilla/EndianUtils.h" directly. The code only works because of unified builds or because the file includes EndianUtils.h indirectly.

When you disturb the house of cards, the symptom is you get is... well, just imagine it. *One* Gecko source file thinks you're on a big-endian machine. Mirror universe. You the programmer aren't expecting that at all. It's maddening to track down. I literally manually rm -rf'd my objdir and rebuilt before I could believe what the debugger was telling me.

If we changed these macros to be function-like, the symptom would be: compiler errors. For these particular macros, I think it's worth doing.

Comment 1

[Nathan Froyd [:froydnj]]

+0x01000000

Comment 2

[Jeff Walden [:Waldo]]

Attachment: Bug 1439659 - Make |MOZ_{LITTLE,BIG}_ENDIAN| into function macros so that invoking them inside |#if| conditions when they haven't been defined yet is a compile error. r=froydnj

Comment 3

[Jeff Walden [:Waldo]]

Perhaps worth noting, when you have function-macros like this it is, um, "less possible" to accidentally use #ifdef with a macro designed to be used with #if. As apparently happened a few places previously, as you can see in certain places in the patch's changes.

Unfortunately it's only "less possible" because at least with my clang, the result I got was a compiler warning about extra tokens at end of those lines. Still, a warning is better than the nothing that was happening before.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/6b57e33999e9
Make |MOZ_{LITTLE,BIG}_ENDIAN| into function macros so that invoking them inside |#if| conditions when they haven't been defined yet is a compile error.  r=froydnj

Comment 5

[Dorel Luca [:dluca]]

https://hg.mozilla.org/mozilla-central/rev/6b57e33999e9

Comment 6

[Jeff Walden [:Waldo]]

Attachment: Bug 1439659 - Fix inadvertent typo (that would have been immediately obvious as compile error in a big-endian build, because of this bug's change, happily). r=froydnj

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/7bebdc108aa3
Fix inadvertent typo (that would have been immediately obvious as compile error in a big-endian build, because of this bug's change, happily).  r=froydnj

Comment 8

[Cristina Coroiu [:ccoroiu]]

https://hg.mozilla.org/mozilla-central/rev/7bebdc108aa3