From 2ec6d1e5250e5a36c919354649c3bc3f17261140 Mon Sep 17 00:00:00 2001
From: Kartik Agaram <vc@akkartik.com>
Date: Sat, 29 Sep 2018 16:17:11 -0700
Subject: 4619 - new syscall: mmap()

---
 subx/examples/ex12      | Bin 0 -> 167 bytes
 subx/examples/ex12.subx |  43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100755 subx/examples/ex12
 create mode 100644 subx/examples/ex12.subx

(limited to 'subx/examples')

diff --git a/subx/examples/ex12 b/subx/examples/ex12
new file mode 100755
index 00000000..236afe98
Binary files /dev/null and b/subx/examples/ex12 differ
diff --git a/subx/examples/ex12.subx b/subx/examples/ex12.subx
new file mode 100644
index 00000000..50c57928
--- /dev/null
+++ b/subx/examples/ex12.subx
@@ -0,0 +1,43 @@
+## example showing mmap syscall
+# Create a new segment using mmap, save the address, write to it.
+#
+# To run:
+#   $ subx translate ex12.subx ex12
+#   $ subx run ex12
+# You shouldn't get a segmentation fault.
+
+== code
+# instruction                     effective address                                                   operand     displacement    immediate
+# op          subop               mod             rm32          base        index         scale       r32
+# 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes
+
+  # mmap(0x1000)
+  bb/copy                         .               .             .           .             .           .           .               mmap_new_segment/imm32  # copy to EBX
+  b8/copy                         .               .             .           .             .           .           .               0x5a/imm32/mmap         # copy 8 to EAX
+  cd/syscall  0x80/imm8
+
+  # store to *EAX
+  c7/copy                         0/mod/direct    0/rm32/EAX    .           .             .           .           .               0x34/imm32              # copy 0x34 to *EAX
+
+  # exit(EAX)
+  89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           0/r32/EAX   .               .                       # copy EAX to EBX
+  b8/copy                         .               .             .           .             .           .           .               1/imm32/exit            # copy 1 to EAX
+  cd/syscall  0x80/imm8
+
+== data
+# various constants used here were found in the Linux sources (search for file mman-common.h)
+mmap_new_segment:  # type mmap_arg_struct
+  # addr
+  00 00 00 00  # null
+  # len
+  00 01 00 00  # 0x1000
+  # protection flags
+  03 00 00 00  # PROT_READ | PROT_WRITE
+  # sharing flags
+  22 00 00 00  # MAP_PRIVATE | MAP_ANONYMOUS
+  # fd
+  ff ff ff ff  # -1 since MAP_ANONYMOUS is specified
+  # offset
+  00 00 00 00  # 0 since MAP_ANONYMOUS is specified
+
+# vim:ft=subx:nowrap:tw&
-- 
cgit 1.4.1-2-gfad0