PLT section

README.md

@@ -3,11 +3,27 @@ The process of [kernel modules compilation](https://www.kernel.org/doc/html/v5.6
 
 > But what to do if, for the variety of reasons, for the kernel you are interest in, headers are unavailable?
 
-This article focuses on Android, but most of information and techniques discussed here can be easily applied to generic Linux kernel as well.
+The code in this repo focuses on Android, but most of the information and techniques discussed here can be easily applied to the generic Linux kernel as well.
 
 # ELF symbols stealing 
 
-The main idea, is to use Android NDK to compile generic Linux kernel module. And embed it with ELF symbols collected from some existing kernel module (see `/vendor/lib/modules/*.ko`). In such a way, that the loader would be able to recognise and resolve all necessary dependencies and definitions.
+The main idea, is to use Android NDK to compile generic Linux kernel module. And embed it with ELF symbols collected from some existing kernel module (see `/vendor/lib/modules/*.ko`). In such a way, that the LKM loader would be able to recognise and resolve all necessary dependencies and definitions.
+
+## PLT section
+
+This part is pretty straight forward, we simply have to define a few ELF symbols, that Android LKM is expecting to find within *normal* module. We are going to really on [compiler keyword](https://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Variable-Attributes.html)  `__attribute__` for this.
+
+```c
+// insmod error: module PLT section(s) missing
+__attribute__((section(".plt")))
+char plt = 0;
+
+__attribute__((section(".init.plt")))
+char initplt = 0;
+
+__attribute__((section(".text.ftrace_trampoline")))
+char textftrace_trampoline = 0; // TODO: probably an overkill
+```
 
 ## .modinfo
 
@@ -73,7 +89,6 @@ readelf -a $KMODULE -W
   0000000000000310  000006ee00000101 R_AARCH64_ABS64        0000000000000000 cleanup_module + 0
 ```
 
-
 ## \_\_versions
 
 In its essence is a byte-array for declaring external dependencies required by the module:

bmod.c

@@ -11,7 +11,7 @@ __attribute__((section(".init.plt")))
 char initplt = 0;
 
 __attribute__((section(".text.ftrace_trampoline")))
-char textftrace_trampoline = 0; // TODO: probably irrelevant 
+char textftrace_trampoline = 0; // TODO: probably an overkill 
 
 
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