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Re: libffi 3.3 release candidate 1


On 10/25/19 10:04 PM, Andreas Schwab wrote:
On Okt 25 2019, John Paul Adrian Glaubitz wrote:
On 10/25/19 8:32 PM, Andreas Schwab wrote:
On Okt 25 2019, John Paul Adrian Glaubitz wrote:
It's qemu-user that we are using here, not qemu-system. qemu-user is more finicky
when it comes to running testsuites.

There is nothing finicky about this testsuite.  It's pure user-space.

Yes, but qemu-user has known bugs

If it cannot even get the user-space ABI right it is useless.

Qemu-user was used for building Nokia Internet tablet + phone products
(Debian derivative) Maemo & Meego OSes (over a decade ago), until
Nokia shut down its Linux efforts (and eventually sold its phone
business to MicroSoft). I think user-space Qemu has in general been
useful for this kind of work quite long time.

Problems can be categorized to few classes:

1. CPU emulation bugs
 - get more rare as emulation matures (new bugs may sometimes
   be found e.g. with new compiler versions)
 - obviously must be fixed for emu to be useful/trustworthy

2. User-space ABI translation
  - rare, but expected to happen occasionally, as kernel & libc change
    (kernel ABI extensions, libc starting to use something that wasn't
     yet translated fully etc)
  - should be easy to catch and in most cases straightforward to fix

3. Threading and other issues related to emulating just user-space
  - not all issues are fixable
  - AFAIK mainly an issue with some test-suites
  - those packages just need to be built with system emulator.
    User-space qemu is used for performance reasons, doing building
    with magnitude slower system emulator is not too bad, as long as
    majority of packages build fine with user-space qemu, and system
    emulator can emulate large enough amount of RAM etc

An obvious conclusion from these is that any bugs with user-space
qemu need to be vetted for whether they belong to above categories,
before forwarding them to package maintainers.

	- Eero

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