Add x32 exploration blog post

Author: joaohf

blog/2023-09-02/index.md

@@ -0,0 +1,105 @@
+---
+title: Exploring x32 psABI for Erlang/OTP
+authors: [joaohf]
+tags: [meta-erlang, x32]
+---
+
+According to [Wikipedia X32 ABI](https://en.wikipedia.org/wiki/X32_ABI) page:
+
+> The x32 ABI is an application binary interface (ABI) and one of the interfaces
+> of the Linux kernel. The x32 ABI provides 32-bit integers, long and pointers
+> (ILP32) on Intel and AMD 64-bit hardware. The ABI allows programs to take
+> advantage of the benefits of x86-64 instruction set (larger number of CPU
+> registers, better floating-point performance, faster position-independent
+> code, shared libraries, function parameters passed via registers, faster
+> syscall instruction) while using 32-bit pointers and thus avoiding the
+> overhead of 64-bit pointers.
+
+So, I'm wondering if it would be possible to enable x32 support in Erlang/OTP
+build. That way, I could make a Yocto image for x32 that runs on x86-64
+machines.
+
+Here is some references about the subject:
+
+- [Yocto, Using x32 psABI](https://docs.yoctoproject.org/dev-manual/x32-psabi.html)
+- [x32-abi](https://sites.google.com/site/x32abi/home?authuser=0)
+- [X32 – A Native 32bit ABI For X86-64](http://linuxplumbersconf.org/2011/ocw//system/presentations/531/original/x32-LPC-2011-0906.pptx)
+- [Debian x32 port](https://wiki.debian.org/X32Port)
+- [System V Application Binary Interface AMD64 Architecture Processor Supplement (With LP64 and ILP32 Programming Models](https://raw.githubusercontent.com/wiki/hjl-tools/x86-psABI/x86-64-psABI-1.0.pdf)
+
+In fact, x32 seems to be around since 2011/2012 and has been integrated in many
+platforms. Like Ubuntu, Debian, Gentoo.
+
+Enabling it for Yocto is simple, just adding the follow snippet in your
+local.conf file:
+
+```
+MACHINE = "qemux86-64"
+DEFAULTTUNE = "x86-64-x32"
+baselib = "${@d.getVar('BASE_LIB:tune-' + (d.getVar('DEFAULTTUNE') or 'INVALID')) or 'lib'}"
+```
+
+Then, building erlang:
+
+```
+bitbake erlang
+```
+
+:::note
+
+For those that want to check all configure and compiler flags, I'm including the
+links to those logs:
+
+- [Configure log output](log.do_configure)
+- [Compile log output](log.do_compile)
+
+:::
+
+The build failed in one point related to ASM code in
+[erts/lib_src/pthread/ethread.c](https://github.com/erlang/otp/blob/maint-26/erts/lib_src/pthread/ethread.c#L193).
+Looks like an ASM incompatibility issue. In order to address it here is
+[a patch](https://github.com/joaohf/otp/commit/6cd15d5888a536af97f5d8e26b2db2e379fa7eab)
+that just adds one more compiler check to pick up the correct ifdef branch.
+
+Afer that, the build runs as expected. And testing it using QEMU shows exactly
+what I had in mind:
+
+```
+runqemu core-image-minimal-qemux86-64.ext4 slirp nographic serialstdio
+```
+
+- check the current kernel
+
+```
+root@qemux86-64:~# uname -a
+Linux qemux86-64 6.1.32-yocto-standard #1 SMP PREEMPT_DYNAMIC Mon Jun  5 13:43:33 UTC 2023 x86_64 GNU/Linux
+```
+
+- check /proc/cpuinfo to see the 'lm' (long mode)
+
+```
+root@qemux86-64:~# grep -o -w 'lm' /proc/cpuinfo
+lm
+```
+
+- check Erlang shell
+
+```
+Erlang/OTP 26 [erts-14.0.2] [source] [32-bit] [smp:4:4] [ds:4:4:10] [async-threads:1]
+
+Eshell V14.0.2 (press Ctrl+G to abort, type help(). for help)
+1> application:ensure_all_started(crypto).
+{ok,[crypto]}
+```
+
+Well, looks like we are running Erlang/OTP 32-bits in a x86_64 machine. Also, it
+was able to correct load the crypto (with ssl libraries compiled for x32 too).
+By the way, there is a second
+[patch need to proper compile the crypto application](https://github.com/joaohf/otp/commit/e63b5b703ffa0005bf6a8f4d3bcec18f786bda92).
+
+Some raised questions for further investigations:
+
+- What tests are necessary to prove that the x32 Erlang build is safe ?
+- Are there any other code change in order to fit the x32 build ?
+- Would [BeamAsm](https://www.erlang.org/doc/apps/erts/beamasm#faq) be available
+  for x32 ?