4619 - new syscall: mmap()

4 files changed, 61 insertions, 1 deletions

diff --git a/subx/020syscalls.cc b/subx/020syscalls.cc
index 2940b06c..5fdc40f6 100644
--- a/subx/020syscalls.cc
+++ b/subx/020syscalls.cc
@@ -77,6 +77,12 @@ void process_int80() {
     trace(91, "run") << "grow data segment to " << Reg[EBX].u << end();
     grow_data_segment(/*new end address*/Reg[EBX].u);
     break;
+  case 90:  // mmap: allocate memory outside existing segment allocations
+    trace(91, "run") << "mmap: allocate new segment" << end();
+    // Ignore most arguments for now: address hint, protection flags, sharing flags, fd, offset.
+    // We only support anonymous maps.
+    Reg[EAX].u = new_segment(/*length*/read_mem_u32(Reg[EBX].u+0x4));
+    break;
   default:
     raise << HEXWORD << EIP << ": unimplemented syscall " << Reg[EAX].u << '\n' << end();
   }
@@ -102,3 +108,14 @@ void check_mode(int reg) {
     exit(1);
   }
 }
+
+:(before "End Globals")
+uint32_t Next_segment = 0xb0000000;  // 0xc0000000 and up is reserved for Linux kernel
+const uint32_t SPACE_FOR_SEGMENT = 0x01000000;
+:(code)
+uint32_t new_segment(uint32_t length) {
+  uint32_t result = Next_segment;
+  Mem.push_back(vma(Next_segment, Next_segment+length));
+  Next_segment -= SPACE_FOR_SEGMENT;
+  return result;
+}
diff --git a/subx/035labels.cc b/subx/035labels.cc
index ddaeabad..75000233 100644
--- a/subx/035labels.cc
+++ b/subx/035labels.cc
@@ -42,7 +42,7 @@ b9/copy aaa/imm32  # copy to ECX
 b9/copy xxx/imm32  # copy to ECX
 +transform: packing instruction 'b9/copy xxx/imm32'
 # no change (we're just not printing metadata to the trace)
-+transform: instruction after packing: 'b9 xx'
++transform: instruction after packing: 'b9 xxx'
 
 //: a helper we'll find handy later
 :(code)
diff --git a/subx/examples/ex12 b/subx/examples/ex12
new file mode 100755
index 00000000..236afe98
--- /dev/null
+++ b/subx/examples/ex12
Binary files differdiff --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&