From 91fcfdf79461fefa712e16b3d327987e0bf42798 Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Thu, 20 Mar 2025 19:29:52 +0100
Subject: gas: initial notes

---
 src/SUMMARY.md            |  1 +
 src/development/README.md |  1 +
 src/development/gas.md    | 42 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+)
 create mode 100644 src/development/gas.md

diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index 29f4eee..145d900 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -71,6 +71,7 @@
     - [c++](./development/c++.md)
     - [glibc](./development/glibc.md)
     - [gcc](./development/gcc.md)
+    - [gas](./development/gas.md)
     - [git](./development/git.md)
     - [cmake](./development/cmake.md)
     - [make](./development/make.md)
diff --git a/src/development/README.md b/src/development/README.md
index 3363308..437528d 100644
--- a/src/development/README.md
+++ b/src/development/README.md
@@ -4,6 +4,7 @@
 - [c++](./c++.md)
 - [glibc](./glibc.md)
 - [gcc](./gcc.md)
+- [gas](./gas.md)
 - [git](./git.md)
 - [cmake](./cmake.md)
 - [make](./make.md)
diff --git a/src/development/gas.md b/src/development/gas.md
new file mode 100644
index 0000000..a3da13f
--- /dev/null
+++ b/src/development/gas.md
@@ -0,0 +1,42 @@
+# gas
+
+## Frequently used directives
+- `.byte`, `.2byte`, `.4byte`, `.8byte` to define a N byte value
+  ```x86asm
+  .byte 0xaa
+  .2byte 0xaabb
+  .2byte 0xaa, 0xbb
+  .4byte 0xaabbccdd
+  .8byte 0xaabbccdd11223344
+  ```
+- `.ascii` to define an ascii string
+  ```x86asm
+  .ascii "foo"   ; allocates 3 bytes
+  ```
+- `.asciz` to define an ascii string with `'\0'` terminator
+  ```x86asm
+  .asciz "foo"   ; allocates 4 bytes (str + \0)
+  ```
+- `.macro` to define assembler macros. Arguments are accessed with the
+  `\arg` syntax.
+  ```x86asm
+  .macro defstr name str
+  \name:
+      .ascii "\str"
+  \name\()_len:
+      .8byte . - \name
+  .endm
+
+  ; use as
+  defstr foo, "foobar"
+  ```
+  > Use `\()` to concatenate macro argument and literal.
+
+
+- [GNU Assembler][gas_doc]
+- [GNU Assembler Directives][gas_directives]
+- [GNU Assembler `x86_64` dependent features][gas_x86_64]
+
+[gas_doc]: https://sourceware.org/binutils/docs/as
+[gas_directives]: https://sourceware.org/binutils/docs/as/Pseudo-Ops.html#Pseudo-Ops
+[gas_x86_64]: https://sourceware.org/binutils/docs/as/i386_002dDependent.html
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