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1 files changed, 43 insertions, 0 deletions

diff --git a/linux/apps/ex12.subx b/linux/apps/ex12.subx
new file mode 100644
index 00000000..476d8cda
--- /dev/null
+++ b/linux/apps/ex12.subx
@@ -0,0 +1,43 @@
+# Example showing mmap syscall.
+# Create a new segment using mmap, save the address, write to it.
+#
+# To run:
+#   $ bootstrap/bootstrap translate apps/ex12.subx -o ex12
+#   $ bootstrap/bootstrap run ex12
+# You shouldn't get a segmentation fault.
+
+== code
+#   instruction                     effective address                                                   register    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
+
+Entry:
+    # mmap(Mmap-new-segment->len)
+    bb/copy-to-ebx  Mmap-new-segment/imm32
+    e8/call  syscall_mmap/disp32
+
+    # write to *eax to check that we have access to the newly-allocated segment
+    c7          0/subop/copy        0/mod/direct    0/rm32/eax    .           .             .           .           .               0x34/imm32        # copy to *eax
+
+    # exit(eax)
+    89/copy                         3/mod/direct    3/rm32/ebx    .           .             .           0/r32/eax   .               .                 # copy eax to ebx
+    e8/call  syscall_exit/disp32
+
+== 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
+    0/imm32
+    # len
+    0x100/imm32
+    # protection flags
+    3/imm32  # PROT_READ | PROT_WRITE
+    # sharing flags
+    0x22/imm32  # MAP_PRIVATE | MAP_ANONYMOUS
+    # fd
+    -1/imm32  # since MAP_ANONYMOUS is specified
+    # offset
+    0/imm32  # since MAP_ANONYMOUS is specified
+
+# . . vim:nowrap:textwidth=0