Changeset e18ba69

Timestamp:

09/30/2022 02:43:19 AM (19 months ago)

Author:

Xi Ruoyao <xry111@…>

Branches:

11.3, 11.3-rc1, 12.0, 12.0-rc1, 12.1, 12.1-rc1, bdubbs/gcc13, multilib, renodr/libudev-from-systemd, trunk, xry111/arm64, xry111/arm64-12.0, xry111/clfs-ng, xry111/loongarch, xry111/loongarch-12.0, xry111/loongarch-12.1, xry111/mips64el, xry111/pip3, xry111/rust-wip-20221008, xry111/update-glibc

Children:

77b46db

Parents:

cc0e77d

git-author:

Xi Ruoyao <xry111@…> (09/30/2022 02:39:03 AM)

git-committer:

Xi Ruoyao <xry111@…> (09/30/2022 02:43:19 AM)

Message:

toolchain technical note: rewrite the descrption for triplet

• Don't say "most building system", refine the dicussion for autoconf. Other building systems may use a variant of triplet, or use a completely different system designation.
• Explain why a triplet may contain 4 fields in detail. "Histroical reason" is not really correct because 3-field triplet is still used today for BSD, Fuchsia, IOS, Mac OS X (darwin), Solaris, etc.
• "machine" triplet to "system" triplet (strictly speaking, only the first field in the triplet is for the machine).

Why we need to say "vendor can be omitted" explicitly: we mention "gcc
-dumpmachine". On some distros (like Ubuntu) the output has no vendor
field. If you think this is too nasty, please remove both.

File:

• part3intro/toolchaintechnotes.xml (modified) (1 diff)

part3intro/toolchaintechnotes.xml

@@ -146 +146 @@
 
     <note>
-      <para>Almost all the build systems use names of the form
-      cpu-vendor-kernel-os, referred to as the machine triplet. (Sometimes,
-      the vendor field is omitted.) An astute
-      reader may wonder why a <quote>triplet</quote> refers to a four component
-      name. The reason is historical: initially, three component names were enough
-      to designate a machine unambiguously, but as new machines and systems
-      proliferated, that proved insufficient. The word <quote>triplet</quote>
-      remained. A simple way to determine your machine triplet is to run
-      the <command>config.guess</command>
+      <para>All packages involved with cross compilation in the book use an
+      autoconf-based building system.  The autoconf-based building system
+      accepts system types in the form cpu-vendor-kernel-os,
+      referred to as the system triplet.  Since the vendor field is mostly
+      irrelevant, autoconf allows to omit it. An astute reader may wonder
+      why a <quote>triplet</quote> refers to a four component name. The
+      reason is the kernel field and the os field originiated from one
+      <quote>system</quote> field.  Such a three-field form is still valid
+      today for some systems, for example
+      <literal>x86_64-unknown-freebsd</literal>.  But for other systems,
+      two systems can share the same kernel but still be too different to
+      use a same triplet for them.  For example, an Android running on a
+      mobile phone is completely different from Ubuntu running on an ARM64
+      server.  Without an emulation layer, you cannot run an executable for
+      the server on the mobile phone or vice versa.  So the
+      <quote>system</quote> field is separated into kernel and os fields to
+      designate these systems unambiguously.  For our example, the Android
+      system is designated <literal>aarch64-unknown-linux-android</literal>,
+      and the Ubuntu system is designated
+      <literal>aarch64-unknown-linux-gnu</literal>.  The word
+      <quote>triplet</quote> remained. A simple way to determine your
+      system triplet is to run the <command>config.guess</command>
       script that comes with the source for many packages. Unpack the binutils
       sources and run the script: <userinput>./config.guess</userinput> and note