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Specialised unsafe.asm to unsafe_mem.asm, and renamed unsafe.memcmp to unsafe.compare

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MutexRaceCondition
2026-09-03 15:22:40 +02:00
parent 3d874cebbd
commit a1e19112c5
1 changed files with 12 additions and 12 deletions
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unsafe.asm → unsafe_mem.asm
+12 -12
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@@ -1,4 +1,4 @@
; int memcmp(uint8_t* a, uint8_t* b, size_t count); ; int compare(uint8_t* a, uint8_t* b, size_t count);
; Compares two memory segment of equal length lexicographically. ; Compares two memory segment of equal length lexicographically.
; Temporarily modifies the byte at address `a + count`. ; Temporarily modifies the byte at address `a + count`.
; ;
@@ -11,7 +11,7 @@
; - `0` if both segments are equal. ; - `0` if both segments are equal.
; - `<0` if the first segment is less than the second segment. ; - `<0` if the first segment is less than the second segment.
; - `>0` if the first segment is greater than the second segment. ; - `>0` if the first segment is greater than the second segment.
pub fn_memcmp: pub compare:
; Exclusive end point of the second segment. ; Exclusive end point of the second segment.
add r4, r3, r2 add r4, r3, r2
; Exclusive end point of the first segment. ; Exclusive end point of the first segment.
@@ -20,13 +20,13 @@ pub fn_memcmp:
load_8 flags, [r4] load_8 flags, [r4]
; Check if the first bytes behind the sequences are equal. ; Check if the first bytes behind the sequences are equal.
cmp flags, r6 cmp flags, r6
jne _memcmp__loop jne _compare__loop
; Change the byte directly behind the first segment. ; Change the byte directly behind the first segment.
xor r4, r6, 1 xor r4, r6, 1
; This would be problematic if someone calls memcmp with a first segment ; This would be problematic if someone calls compare with a first segment
; whose end point overlaps the program memory of this function. ; whose end point overlaps the program memory of this function.
store_8 [r3], r4 store_8 [r3], r4
_memcmp__loop: _compare__loop:
load_32 r4, [r1] load_32 r4, [r1]
add r1, r1, 4 add r1, r1, 4
load_32 r5, [r2] load_32 r5, [r2]
@@ -34,7 +34,7 @@ _memcmp__loop:
; Comparing two sequences of 4 bytes lexicographically is equivalent to ; Comparing two sequences of 4 bytes lexicographically is equivalent to
; comparing the corresponding big endian 32 bit words. ; comparing the corresponding big endian 32 bit words.
cmp r4, r5 cmp r4, r5
je _memcmp__loop je _compare__loop
; We overshot in the loop; decrement r1 again. (Only by 2, we backtrack the rest if necessary later) ; We overshot in the loop; decrement r1 again. (Only by 2, we backtrack the rest if necessary later)
sub r1, r1, 2 sub r1, r1, 2
; Restore the byte we changed. ; Restore the byte we changed.
@@ -45,24 +45,24 @@ _memcmp__loop:
mov r5, flags mov r5, flags
; Check if at least one of the two most significant bytes is not 0. ; Check if at least one of the two most significant bytes is not 0.
cmp r4, 0xffff cmp r4, 0xffff
jbe _memcmp__low2 jbe _compare__low2
; If it is, backtrack the remaining 2 indices. ; If it is, backtrack the remaining 2 indices.
; Shift the most significant bytes to the least significant ones. ; Shift the most significant bytes to the least significant ones.
sub r1, r1, 2 sub r1, r1, 2
lsr r4, r4, 16 lsr r4, r4, 16
_memcmp__low2: _compare__low2:
; r1 now points to a non-zero 16 bit value. ; r1 now points to a non-zero 16 bit value.
; If the 16 bit value at r1-2 is in-bounds, then it is 0. ; If the 16 bit value at r1-2 is in-bounds, then it is 0.
; Check if the most significant byte of the 16 bit value is 0. ; Check if the most significant byte of the 16 bit value is 0.
cmp r4, 0xff cmp r4, 0xff
ja _memcmp__low1 ja _compare__low1
; If it is, our target is the least significant byte. ; If it is, our target is the least significant byte.
add r1, r1, 1 add r1, r1, 1
_memcmp__low1: _compare__low1:
; Otherwise, the target is that non-zero byte. ; Otherwise, the target is that non-zero byte.
; Check if the target is out of bounds, i.e. the loop terminated through the "bounds check". ; Check if the target is out of bounds, i.e. the loop terminated through the "bounds check".
cmp r1, r3 cmp r1, r3
jae _memcmp__oob jae _compare__oob
; r5 is the comparison result in the format of `cmp`. Convert it to the desired format. ; r5 is the comparison result in the format of `cmp`. Convert it to the desired format.
; 00 => 0x40000000 > 0 ; 00 => 0x40000000 > 0
; 01 => 0x00000000 = 0 ; 01 => 0x00000000 = 0
@@ -70,6 +70,6 @@ _memcmp__low1:
xor r1, r5, 1 xor r1, r5, 1
lsl r1, r1, 30 lsl r1, r1, 30
jmp r13 jmp r13
_memcmp__oob: _compare__oob:
mov r1, 0 mov r1, 0
jmp r13 jmp r13