From 3d72c232258632969c1f2d2797cbbdaff8720e24 Mon Sep 17 00:00:00 2001
From: FreeArtMan <dos21h@gmail.com>
Date: Sun, 29 May 2016 21:39:29 +0100
Subject: [POST] added gcc inline assembly notes

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 md/writeup.md                     |   1 +
 md/writeup/gcc_inline_assembly.md | 183 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 184 insertions(+)
 create mode 100644 md/writeup/gcc_inline_assembly.md

(limited to 'md')

diff --git a/md/writeup.md b/md/writeup.md
index 96deda8..e3758f7 100644
--- a/md/writeup.md
+++ b/md/writeup.md
@@ -11,6 +11,7 @@
 [Multiboot USB drive](writeup/multiboot_usb_drive.md)  
 [Solving crackmes](writeup/crackme.md)  
 [Using iptables](writeup/using_iptables.md)  
+[GCC inline assembly](writeup/gcc_inline_assembly.md)  
 
 ## Projects
 
diff --git a/md/writeup/gcc_inline_assembly.md b/md/writeup/gcc_inline_assembly.md
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+# GCC inline assembly
+
+Here is attempt to make best notes about gcc inline asm. As this is just small
+operator that is for long time, i dont thing there is some full guide how to use
+it lets do it here for wisdom of internet.
+
+## Inline assembly syntax
+
+```
+asm [volatile] ( 
+        AssemblerTemplate
+        : OutputOperands
+        [ : InputOperands
+        [ : Clobbers ] ]
+)
+```
+
+### Output operands
+
+| Option | Note |
+|---|---|
+| "=r" | Write output to register |
+
+### Input operands
+
+| Option | Note |
+|---|---|
+| "r" | Input to register |
+
+### Clobbers 
+
+Clobbers used to tell GCC that registers are used. 
+
+| Clobber option | Note |
+|---|---|
+| "0" | map to register "0" same register |
+
+### Modifiers
+
+|Modifier|Specifies|
+|---|---|
+| = | Write-only operand, usually used for all output operands |
+| + | Read-write operand, must be listed as an output operand |
+| & | A register that should be used for output only |
+
+### Table of register names
+
+Table of AMD64 register names
+
+```text
++---+--------------------+  
+| r |    Register(s)     |  
++---+--------------------+  
+| a |   %eax, %ax, %al   |  
+| b |   %ebx, %bx, %bl   |  
+| c |   %ecx, %cx, %cl   |  
+| d |   %edx, %dx, %dl   |  
+| S |   %esi, %si        |  
+| D |   %edi, %di        |  
++---+--------------------+  
+```
+
+|Register|Name|
+|---|---|
+| rax | %%rax |
+| rbx | %%rbx |
+| rcx | %%rcx |
+| rdx | %%rdx |
+| rdi | %%rdi |
+| rsi | %%rsi |
+| rbp | %%rbp |
+| rsp | %%rsp |
+| r8  | %%r8  |
+| r9  | %%r9  |
+| r10 | %%r10 |
+| r11 | %%r11 |
+| r12 | %%r12 |
+| r13 | %%r13 |
+| r14 | %%r14 |
+| r15 | %%r15 |
+
+## Syscall calling convention
+
+<!--### Intel i386 Linux-->
+
+### Intel AMD64 Linux
+
+| Param | Register |
+| --- | --- | 
+| 1th            | __rdi__ |
+| 2th            | __rsi__ |
+| 3th            | __rdx__ |
+| 4th            | __rcx__ |
+| 5th            | __r8__  |
+| 6th            | __r9__  |
+| syscall number | __rax__ |
+
+## Example
+
+### AMD64 Add two numbers
+
+```
+int32_t a=1,b=2,c=-1;
+asm(	
+	"movl %1, %0\n\t"
+	"addl %2, %0\n\t"
+	:"=r"(c)
+	:"r"(a),"r"(b)
+	:"0");
+```
+__a__,__b__ - use regisers and save result __c__ to register, 
+make to use for __c__ same register by mentioning "0" in clobber register
+
+__Output__
+```
+	movl %edx, %edx
+	addl %ecx, %edx
+```
+
+```
+int32_t a=1,b=2,c=-1;
+asm(	
+	"movl %1, %0\n\t"
+	"addl %2, %0\n\t"
+	:"=r"(c)
+	:"g"(a),"g"(b)
+	:"0");
+```
+
+__Output__
+```
+	movl -4(%rbp), %edx
+	addl -8(%rbp), %edx
+```
+
+### AMD64 Call linux syscall mmap with inline asm
+
+```
+long sys_mmap(unsigned long addr, unsigned long len, unsigned long prot, unsigned long flags, unsigned long fd, unsigned long off)
+{
+	long ret;
+	asm(
+		"mov %p6, %%r9\n\t"
+		"mov %p5, %%r8\n\t"
+		"mov %p4, %%r10\n\t"
+		"mov %p3, %%rdx\n\t"
+		"mov %p2, %%rsi\n\t"
+		"mov %p1, %%rdi\n\t"
+		"mov $9, %%rax\n\t"
+		"syscall\n\t"
+		:"=a"(ret)
+		:[p1]"m"(addr),[p2]"m"(len),[p3]"m"(prot),[p4]"m"(flags),[p5]"m"(fd),[p6]"m"(off));
+	return ret;
+}
+```
+Put result of execution to __ret__, all paramters in memory
+
+<!--
+
+### Intel i386 BSD
+### Intel AMD64 BSD
+### ARM
+### MIPS
+
+-->
+
+## Switching on of intel/att syntax
+
+## Asm goto
+
+
+
+## Links
+
+1. https://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html
+2. https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
+3. https://en.wikipedia.org/wiki/Inline_assembler
+4. http://www.ethernut.de/en/documents/arm-inline-asm.html
+5. http://wiki.osdev.org/Inline_Assembly
+6. http://asm.sourceforge.net/articles/rmiyagi-inline-asm.txt
+7. http://wiki.osdev.org/Inline_Assembly/Examples
+8. http://wiki.osdev.org/Calling_Conventions
+
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