From de8a15e9f0070a445c9627da4da22f4fc37782de Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Tue, 17 Nov 2020 18:24:38 -0800 Subject: 7262 --- html/313index-bounds-check.subx.html | 146 +++++++++++++++++++++++++++++++++++ 1 file changed, 146 insertions(+) create mode 100644 html/313index-bounds-check.subx.html (limited to 'html/313index-bounds-check.subx.html') diff --git a/html/313index-bounds-check.subx.html b/html/313index-bounds-check.subx.html new file mode 100644 index 00000000..06197c02 --- /dev/null +++ b/html/313index-bounds-check.subx.html @@ -0,0 +1,146 @@ + + + + +Mu - 313index-bounds-check.subx + + + + + + + + + + +https://github.com/akkartik/mu/blob/master/313index-bounds-check.subx +
+ 1 # Helper to check an array's bounds, and to abort if they're violated.
+ 2 # Really only intended to be called from code generated by mu.subx.
+ 3 
+ 4 == code
+ 5 
+ 6 __check-mu-array-bounds:  # index: int, elem-size: int, arr-size: int, function-name: (addr array byte), array-name: (addr array byte)
+ 7     # . prologue
+ 8     55/push-ebp
+ 9     89/<- %ebp 4/r32/esp
+10     # . save registers
+11     50/push-eax
+12     51/push-ecx
+13     52/push-edx
+14     # . not bothering saving ebx; it's only clobbered if we're going to abort
+15     # ecx = arr-size
+16     8b/-> *(ebp+0x10) 1/r32/ecx
+17     # var overflow/edx: int = 0
+18     ba/copy-to-edx 0/imm32
+19     # var offset/eax: int = index * elem-size
+20     8b/-> *(ebp+8) 0/r32/eax
+21     f7 4/subop/multiply-eax-with *(ebp+0xc)
+22     # check for overflow
+23     81 7/subop/compare %edx 0/imm32
+24     0f 85/jump-if-!= __check-mu-array-bounds:overflow/disp32
+25     # check bounds
+26     39/compare %eax 1/r32/ecx
+27     0f 82/jump-if-unsigned< $__check-mu-array-bounds:end/disp32  # negative index should always abort
+28     # abort if necessary
+29     (write-buffered Stderr "fn ")
+30     (write-buffered Stderr *(ebp+0x14))
+31     (write-buffered Stderr ": offset ")
+32     (write-int32-hex-buffered Stderr %eax)
+33     (write-buffered Stderr " is too large for array '")
+34     (write-buffered Stderr *(ebp+0x18))
+35     (write-buffered Stderr "'\n")
+36     (flush Stderr)
+37     # exit(1)
+38     bb/copy-to-ebx 1/imm32
+39     e8/call syscall_exit/disp32
+40 $__check-mu-array-bounds:end:
+41     # . restore registers
+42     5a/pop-to-edx
+43     59/pop-to-ecx
+44     58/pop-to-eax
+45     # . epilogue
+46     89/<- %esp 5/r32/ebp
+47     5d/pop-to-ebp
+48     c3/return
+49 
+50 __check-mu-array-bounds:overflow:
+51     # "fn " function-name ": offset to array '" array-name "' overflowed 32 bits\n"
+52     (write-buffered Stderr "fn ")
+53     (write-buffered Stderr *(ebp+0x14))
+54     (write-buffered Stderr ": offset to array '")
+55     (write-buffered Stderr *(ebp+0x18))
+56     (write-buffered Stderr "' overflowed 32 bits\n")
+57     (flush Stderr)
+58     # exit(1)
+59     bb/copy-to-ebx 1/imm32
+60     e8/call syscall_exit/disp32
+61 
+62 # potential alternative
+63 
+64 #? __bounds-check:  # msg: (addr array byte)
+65 #?   (write-buffered Stderr "abort: array bounds exceeded in fn ")
+66 #?   8b/-> *(esp+4) 0/r32/eax  # we're going to abort, so just clobber away
+67 #?   (write-buffered Stderr %eax)
+68 #?   (write-buffered Stderr Newline)
+69 #?   # exit(1)
+70 #?   bb/copy-to-ebx 1/imm32
+71 #?   e8/call syscall_exit/disp32
+72 
+73 # to be called as follows:
+74 #   var/reg <- index arr/rega: (addr array T), idx/regi: int
+75 #     | if size-of(T) is 1, 2, 4 or 8
+76 #         => # temporarily save array size to reg to check bounds
+77 #            "8b/-> *" rega " " reg "/r32"
+78 #            "c1/shift 5/subop/right %" reg " " log2(size-of(T)) "/imm32"
+79 #            "3b/compare " reg "/r32 *" rega
+80 #            "68/push \"" function "\"/imm32"  # pass function name to error message
+81 #            "0f 8d/jump-if->= __bounds_check/disp32"
+82 #            "81 0/subop/add %esp 4/imm32"  # drop function name
+83 #            # actually save the index addr in reg
+84 #            "8d/copy-address *(" rega "+" regi "<<" log2(size-of(T)) "+4) " reg "/r32"
+
+ + + -- cgit 1.4.1-2-gfad0