On Wed, 29 Nov 2023, Martin Storsjö wrote:
and related code in Chromium [2].
The first doesn't mention ARM, but both use const_seg on 64-bits
arches and data_seg on 32 bits.
I wouldn't really take that as an authority for this matter here - I would
expect this to be a similar historical mistake; someone has used _WIN64 to
distinguish x86 and x64 at a time when no other architectures were relevant
in Windows code.
[1]:
https://lallouslab.net/2017/05/30/using-cc-tls-callbacks-in-visual-studio-with-your-32-or-64bits-programs/
[2]:
https://chromium.googlesource.com/chromium/src/+/lkgr/base/win/dllmain.cc#64
I'll try to write a sensible repro case and build it on all arches. I
don't have ARM Windows machines, I hope that looking at the
cross-compiled executable sections will be enough.
Sure, hopefully inspecting that is enough. Otherwise I can help out running
any test binaries you want to inspect (you can probably mail me off-list for
that).
I went ahead and tested this myself - and as expected, _WIN64 is indeed
the wrong condition.
ARM and ARM64 all use the same section type as x64, it's only x86 which is
the odd one out. So like most other similar cases, you'll need to ifdef
for e.g. _M_IX86 and use the other common codepath for the rest. It might
be good to add a comment that explicitly clarifies which one each of the 4
architectures needs (to indicate that the ifdef isn't a mistake but an
intentional choice).
// Martin
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