diff options
Diffstat (limited to 'linux/apps/ex12.subx')
-rw-r--r-- | linux/apps/ex12.subx | 43 |
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 |