Update gcc inline assembly

1 files changed, 27 insertions, 0 deletions

diff --git a/md/writeup/gcc_inline_assembly.md b/md/writeup/gcc_inline_assembly.md
index 6e9985a..eda7764 100644
--- a/md/writeup/gcc_inline_assembly.md
+++ b/md/writeup/gcc_inline_assembly.md
@@ -155,6 +155,25 @@ long sys_mmap(unsigned long addr, unsigned long len, unsigned long prot, unsigne
 ```
 Put result of execution to __ret__, all paramters in memory
 
+### Intel random number with RDRAND
+
+```
+uint64_t get_hw_rand()
+{
+	uint64_t ret;
+	int i=0;
+	const int timeout = 10;
+	while (i<timeout)
+	{
+		asm("rdrand %0\n\t"
+			:"=a"(ret)::);
+		if (ret) break;
+		i++;
+	}
+	return ret;
+}
+```
+
 <!--
 
 ### Intel i386 BSD
@@ -166,6 +185,14 @@ Put result of execution to __ret__, all paramters in memory
 
 ## Switching on of intel/att syntax
 
+Inline assembler for GCC by default uses AT&T syntax. There is possible to turn on/off intel syntax.
+
+```
+asm(".intel_syntax noprefix");
+asm("mov eax, 1");
+asm(".att_syntax prefix");
+```
+
 ## Asm goto