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Remove undefined behavior from shifts

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`asl` and `asr` in `src/link/patch.c` courtesy of @pinobatch, and rearranged in RGBASM
evaluators.
This commit is contained in:
ISSOtm
2020-01-17 09:08:49 +01:00
parent 1bd41bf79a
commit b11d121c48
10 changed files with 244 additions and 37 deletions
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1
include/asm/warning.h
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@@ -20,6 +20,7 @@ enum WarningID {
WARNING_OBSOLETE,
WARNING_SHIFT,
WARNING_USER,
WARNING_SHIFT_AMOUNT,
NB_WARNINGS,

62
src/asm/constexpr.c
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@@ -205,28 +205,52 @@ void constexpr_BinaryOp(struct ConstExpression *expr,
result = value1 & value2;
break;
case T_OP_SHL:
if (value1 < 0)
warning(WARNING_SHIFT, "Left shift of negative value: %d",
value1);
if (value2 < 0)
fatalerror("Shift by negative value: %d",
value2);
else if (value2 >= 32)
fatalerror("Shift by too big value: %d",
value2);
result = (uint32_t)value1 << value2;
break;
case T_OP_SHR:
if (value2 < 0)
fatalerror("Shift by negative value: %d",
value2);
else if (value2 >= 32)
fatalerror("Shift by too big value: %d",
value2);
warning(WARNING_SHIFT_AMOUNT, "Shifting %s by negative amount %d",
op == T_OP_SHL ? "left" : "right",
value2);
if (op == T_OP_SHR) {
value2 = -value2; /* Right shift == neg left */
result = value1 >> value2;
if (value1 < 0)
warning(WARNING_SHIFT, "Shifting negative value %d",
value1);
}
if (value2 >= 0) {
// Shift left
if (value2 >= 32) {
warning(WARNING_SHIFT_AMOUNT, "Shifting left by large amount %d",
value2);
result = 0;
} else {
/*
* Use unsigned to force a bitwise shift
* Casting back is OK because the types
* implement two's complement behavior
*/
result = (uint32_t)value1 << value2;
}
} else {
// Shift right
value2 = -value2;
if (value2 >= 32) {
warning(WARNING_SHIFT_AMOUNT, "Shifting right by large amount %d",
value2);
result = value1 < 0 ? -1 : 0;
} else if (value1 >= 0) {
result = value1 >> value2;
} else {
/*
* The C standard leaves shifting right
* negative values undefined, so use a
* left shift manually sign-extended
*/
result = (uint32_t)value1 >> value2 |
-((uint32_t)1 << (32 - value2));
}
}
break;
case T_OP_MUL:
result = (uint32_t)value1 * (uint32_t)value2;

60
src/asm/rpn.c
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@@ -409,22 +409,59 @@ void rpn_AND(struct Expression *expr, const struct Expression *src1,
expr->nRPNPatchSize++;
}
static int32_t shift(int32_t shiftee, int32_t amount)
{
if (shiftee < 0)
warning(WARNING_SHIFT, "Shifting negative value %d", shiftee);
if (amount >= 0) {
// Left shift
if (amount >= 32) {
warning(WARNING_SHIFT_AMOUNT, "Shifting left by large amount %d",
amount);
return 0;
} else {
/*
* Use unsigned to force a bitwise shift
* Casting back is OK because the types implement two's
* complement behavior
*/
return (uint32_t)shiftee << amount;
}
} else {
// Right shift
amount = -amount;
if (amount >= 32) {
warning(WARNING_SHIFT_AMOUNT, "Shifting right by large amount %d",
amount);
return shiftee < 0 ? -1 : 0;
} else if (shiftee >= 0) {
return shiftee >> amount;
} else {
/*
* The C standard leaves shifting right negative values
* undefined, so use a left shift manually sign-extended
*/
return (uint32_t)shiftee >> amount
| -((uint32_t)1 << (32 - amount));
}
}
}
void rpn_SHL(struct Expression *expr, const struct Expression *src1,
const struct Expression *src2)
{
mergetwoexpressions(expr, src1, src2);
if (!expr->isReloc) {
if (src1->nVal < 0)
warning(WARNING_SHIFT, "Left shift of negative value: %d",
src1->nVal);
if (src2->nVal < 0)
fatalerror("Shift by negative value: %d", src2->nVal);
else if (src2->nVal >= 32)
fatalerror("Shift by too big value: %d", src2->nVal);
warning(WARNING_SHIFT_AMOUNT, "Shifting left by negative value: %d",
src2->nVal);
expr->nVal = ((uint32_t)src1->nVal << src2->nVal);
expr->nVal = shift(src1->nVal, src2->nVal);
}
pushbyte(expr, RPN_SHL);
@@ -438,11 +475,10 @@ void rpn_SHR(struct Expression *expr, const struct Expression *src1,
if (!expr->isReloc) {
if (src2->nVal < 0)
fatalerror("Shift by negative value: %d", src2->nVal);
else if (src2->nVal >= 32)
fatalerror("Shift by too big value: %d", src2->nVal);
warning(WARNING_SHIFT_AMOUNT, "Shifting right by negative value: %d",
src2->nVal);
expr->nVal = (src1->nVal >> src2->nVal);
expr->nVal = shift(src1->nVal, -src2->nVal);
}
pushbyte(expr, RPN_SHR);

3
src/asm/warning.c
View File

@@ -36,6 +36,7 @@ static enum WarningState const defaultWarnings[NB_WARNINGS] = {
WARNING_DISABLED, /* Obsolete things */
WARNING_DISABLED, /* Shifting undefined behavior */
WARNING_ENABLED, /* User warnings */
WARNING_DISABLED, /* Strange shift amount */
};
static enum WarningState warningStates[NB_WARNINGS];
@@ -70,6 +71,7 @@ static char const *warningFlags[NB_WARNINGS_ALL] = {
"obsolete",
"shift",
"user",
"shift-amount",
/* Meta warnings */
"all",
@@ -106,6 +108,7 @@ static uint8_t const _weverythingCommands[] = {
WARNING_OBSOLETE,
WARNING_SHIFT,
WARNING_USER,
WARNING_SHIFT_AMOUNT,
META_WARNING_DONE
};

46
src/link/patch.c
View File

@@ -18,6 +18,47 @@
#include "extern/err.h"
static int32_t asl(int32_t value, int32_t shiftamt); // Forward decl for below
static int32_t asr(int32_t value, int32_t shiftamt)
{
uint32_t uvalue = value;
// Get the easy cases out of the way
if (shiftamt == 0)
return value;
if (value == 0 || shiftamt <= -32)
return 0;
if (shiftamt > 31)
return (value < 0) ? -1 : 0;
if (shiftamt < 0)
return asl(value, -shiftamt);
if (value > 0)
return uvalue >> shiftamt;
{
// Calculate an OR mask for sign extension
// 1->0x80000000, 2->0xC0000000, ..., 31->0xFFFFFFFE
uint32_t shiftamt_high_bits = -((uint32_t)1 << (32 - shiftamt));
return (uvalue >> shiftamt) | shiftamt_high_bits;
}
}
static int32_t asl(int32_t value, int32_t shiftamt)
{
// Repeat the easy cases here to avoid INT_MIN funny business
if (shiftamt == 0)
return value;
if (value == 0 || shiftamt >= 32)
return 0;
if (shiftamt < -31)
return (value < 0) ? -1 : 0;
if (shiftamt < 0)
return asr(value, -shiftamt);
return (uint32_t)value << shiftamt;
}
/* This is an "empty"-type stack */
struct RPNStack {
int32_t *buf;
@@ -182,14 +223,13 @@ static int32_t computeRPNExpr(struct Patch const *patch,
value = popRPN() <= value;
break;
/* FIXME: sanitize shifts */
case RPN_SHL:
value = popRPN();
value = popRPN() << value;
value = asl(popRPN(), value);
break;
case RPN_SHR:
value = popRPN();
value = popRPN() >> value;
value = asr(popRPN(), value);
break;
case RPN_BANK_SYM:

4
test/asm/overflow.err
View File

@@ -2,10 +2,8 @@ warning: overflow.asm(24): [-Wdiv]
Division of min value by -1
warning: overflow.asm(25): [-Wdiv]
Division of min value by -1
warning: overflow.asm(34): [-Wshift]
Left shift of negative value: -1
warning: overflow.asm(35): [-Wshift]
Left shift of negative value: -1
Shifting negative value -1
warning: overflow.asm(39): [-Wlarge-constant]
Integer constant '4294967296' is too large
warning: overflow.asm(42): [-Wlarge-constant]

27
test/asm/shift.asm Normal file
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@@ -0,0 +1,27 @@
test: macro
; Test the rpn system, as well as the linker...
dl \1 + zero
; ...as well as the constexpr system
result\@ equ \1
printt "\1 = {result\@}\n"
endm
section "test", ROM0[0]
test 1 << 1
test 1 << 32
test 1 << 9001
test -1 << 1
test -1 << 32
test -1 << -9001
test -1 >> 1
test -1 >> 32
test -1 >> 9001
test -4 >> 1
test -4 >> 2
test -1 >> -9001
SECTION "Zero", ROM0[0]
zero:

66
test/asm/shift.err Normal file
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@@ -0,0 +1,66 @@
warning: shift.asm(13) -> shift.asm::test(3): [-Wshift-amount]
Shifting left by large amount 32
warning: shift.asm(13) -> shift.asm::test(6): [-Wshift-amount]
Shifting left by large amount 32
warning: shift.asm(14) -> shift.asm::test(3): [-Wshift-amount]
Shifting left by large amount 9001
warning: shift.asm(14) -> shift.asm::test(6): [-Wshift-amount]
Shifting left by large amount 9001
warning: shift.asm(15) -> shift.asm::test(3): [-Wshift]
Shifting negative value -1
warning: shift.asm(16) -> shift.asm::test(3): [-Wshift]
Shifting negative value -1
warning: shift.asm(16) -> shift.asm::test(3): [-Wshift-amount]
Shifting left by large amount 32
warning: shift.asm(16) -> shift.asm::test(6): [-Wshift-amount]
Shifting left by large amount 32
warning: shift.asm(17) -> shift.asm::test(3): [-Wshift-amount]
Shifting left by negative value: -9001
warning: shift.asm(17) -> shift.asm::test(3): [-Wshift]
Shifting negative value -1
warning: shift.asm(17) -> shift.asm::test(3): [-Wshift-amount]
Shifting right by large amount 9001
warning: shift.asm(17) -> shift.asm::test(6): [-Wshift-amount]
Shifting left by negative amount -9001
warning: shift.asm(17) -> shift.asm::test(6): [-Wshift-amount]
Shifting right by large amount 9001
warning: shift.asm(19) -> shift.asm::test(3): [-Wshift]
Shifting negative value -1
warning: shift.asm(19) -> shift.asm::test(6): [-Wshift]
Shifting negative value -1
warning: shift.asm(20) -> shift.asm::test(3): [-Wshift]
Shifting negative value -1
warning: shift.asm(20) -> shift.asm::test(3): [-Wshift-amount]
Shifting right by large amount 32
warning: shift.asm(20) -> shift.asm::test(6): [-Wshift]
Shifting negative value -1
warning: shift.asm(20) -> shift.asm::test(6): [-Wshift-amount]
Shifting right by large amount 32
warning: shift.asm(21) -> shift.asm::test(3): [-Wshift]
Shifting negative value -1
warning: shift.asm(21) -> shift.asm::test(3): [-Wshift-amount]
Shifting right by large amount 9001
warning: shift.asm(21) -> shift.asm::test(6): [-Wshift]
Shifting negative value -1
warning: shift.asm(21) -> shift.asm::test(6): [-Wshift-amount]
Shifting right by large amount 9001
warning: shift.asm(22) -> shift.asm::test(3): [-Wshift]
Shifting negative value -4
warning: shift.asm(22) -> shift.asm::test(6): [-Wshift]
Shifting negative value -4
warning: shift.asm(23) -> shift.asm::test(3): [-Wshift]
Shifting negative value -4
warning: shift.asm(23) -> shift.asm::test(6): [-Wshift]
Shifting negative value -4
warning: shift.asm(24) -> shift.asm::test(3): [-Wshift-amount]
Shifting right by negative value: -9001
warning: shift.asm(24) -> shift.asm::test(3): [-Wshift]
Shifting negative value -1
warning: shift.asm(24) -> shift.asm::test(3): [-Wshift-amount]
Shifting left by large amount 9001
warning: shift.asm(24) -> shift.asm::test(6): [-Wshift-amount]
Shifting right by negative amount -9001
warning: shift.asm(24) -> shift.asm::test(6): [-Wshift]
Shifting negative value -1
warning: shift.asm(24) -> shift.asm::test(6): [-Wshift-amount]
Shifting left by large amount 9001

12
test/asm/shift.out Normal file
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@@ -0,0 +1,12 @@
1 << 1 = $2
1 << 32 = $0
1 << 9001 = $0
-1 << 1 = $FFFFFFFE
-1 << 32 = $0
-1 << -9001 = $FFFFFFFF
-1 >> 1 = $FFFFFFFF
-1 >> 32 = $FFFFFFFF
-1 >> 9001 = $FFFFFFFF
-4 >> 1 = $FFFFFFFE
-4 >> 2 = $FFFFFFFF
-1 >> -9001 = $0

BIN
test/asm/shift.out.bin Normal file
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