cli/q
Code Issues 1 Pull Requests Activity

Implemented position independent addresses for x86

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This commit is contained in:
Eduard Urbach
2025-03-07 11:39:13 +01:00
parent 0ac7fc9a85
commit 0bf299d007
3 changed files with 68 additions and 13 deletions
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28
src/asmc/move.go
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@ -4,7 +4,6 @@ import (
"strings"
"git.urbach.dev/cli/q/src/asm"
"git.urbach.dev/cli/q/src/config"
"git.urbach.dev/cli/q/src/x86"
)
@ -17,40 +16,43 @@ func (c *compiler) move(x asm.Instruction) {
c.code = x86.MoveRegisterRegister(c.code, operands.Destination, operands.Source)
case *asm.RegisterLabel:
start := len(c.code)
c.code = x86.MoveRegisterNumber(c.code, operands.Register, 0x00_00_00_00)
size := 4
opSize := len(c.code) - size - start
regLabel := x.Data.(*asm.RegisterLabel)
start := Address(len(c.code))
c.code = x86.LoadAddress(c.code, operands.Register, 0x00_00_00_00)
end := Address(len(c.code))
size := uint32(4)
position := end - size
opSize := position - start
if strings.HasPrefix(regLabel.Label, "data ") {
if strings.HasPrefix(operands.Label, "data ") {
c.dataPointers = append(c.dataPointers, &pointer{
Position: Address(len(c.code) - size),
Position: position,
OpSize: uint8(opSize),
Size: uint8(size),
Resolve: func() Address {
destination, exists := c.dataLabels[regLabel.Label]
destination, exists := c.dataLabels[operands.Label]
if !exists {
panic("unknown label")
}
return config.BaseAddress + c.dataStart + destination + 8
destination += c.dataStart - c.codeStart
distance := destination - end
return distance + 8
},
})
} else {
c.codePointers = append(c.codePointers, &pointer{
Position: Address(len(c.code) - size),
Position: position,
OpSize: uint8(opSize),
Size: uint8(size),
Resolve: func() Address {
destination, exists := c.codeLabels[regLabel.Label]
destination, exists := c.codeLabels[operands.Label]
if !exists {
panic("unknown label")
}
return config.BaseAddress + c.codeStart + destination
return destination - end
},
})
}

13
src/x86/LoadAddress.go Normal file
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@ -0,0 +1,13 @@
package x86
import (
"encoding/binary"
"git.urbach.dev/cli/q/src/cpu"
)
// LoadAddress calculates the address with the RIP-relative offset and writes the result to the destination register.
func LoadAddress(code []byte, destination cpu.Register, offset int) []byte {
code = encode(code, AddressMemory, destination, 0b101, 8, 0x8D)
return binary.LittleEndian.AppendUint32(code, uint32(offset))
}

40
src/x86/LoadAddress_test.go Normal file
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@ -0,0 +1,40 @@
package x86_test
import (
"testing"
"git.urbach.dev/cli/q/src/cpu"
"git.urbach.dev/cli/q/src/x86"
"git.urbach.dev/go/assert"
)
func TestLoadAddress(t *testing.T) {
usagePatterns := []struct {
Destination cpu.Register
Offset int
Code []byte
}{
{x86.RAX, 0, []byte{0x48, 0x8D, 0x05, 0x00, 0x00, 0x00, 0x00}},
{x86.RCX, 0, []byte{0x48, 0x8D, 0x0D, 0x00, 0x00, 0x00, 0x00}},
{x86.RDX, 0, []byte{0x48, 0x8D, 0x15, 0x00, 0x00, 0x00, 0x00}},
{x86.RBX, 0, []byte{0x48, 0x8D, 0x1D, 0x00, 0x00, 0x00, 0x00}},
{x86.RSP, 0, []byte{0x48, 0x8D, 0x25, 0x00, 0x00, 0x00, 0x00}},
{x86.RBP, 0, []byte{0x48, 0x8D, 0x2D, 0x00, 0x00, 0x00, 0x00}},
{x86.RSI, 0, []byte{0x48, 0x8D, 0x35, 0x00, 0x00, 0x00, 0x00}},
{x86.RDI, 0, []byte{0x48, 0x8D, 0x3D, 0x00, 0x00, 0x00, 0x00}},
{x86.R8, 0, []byte{0x4C, 0x8D, 0x05, 0x00, 0x00, 0x00, 0x00}},
{x86.R9, 0, []byte{0x4C, 0x8D, 0x0D, 0x00, 0x00, 0x00, 0x00}},
{x86.R10, 0, []byte{0x4C, 0x8D, 0x15, 0x00, 0x00, 0x00, 0x00}},
{x86.R11, 0, []byte{0x4C, 0x8D, 0x1D, 0x00, 0x00, 0x00, 0x00}},
{x86.R12, 0, []byte{0x4C, 0x8D, 0x25, 0x00, 0x00, 0x00, 0x00}},
{x86.R13, 0, []byte{0x4C, 0x8D, 0x2D, 0x00, 0x00, 0x00, 0x00}},
{x86.R14, 0, []byte{0x4C, 0x8D, 0x35, 0x00, 0x00, 0x00, 0x00}},
{x86.R15, 0, []byte{0x4C, 0x8D, 0x3D, 0x00, 0x00, 0x00, 0x00}},
}
for _, pattern := range usagePatterns {
t.Logf("lea %s, [rip+%d]", pattern.Destination, pattern.Offset)
code := x86.LoadAddress(nil, pattern.Destination, pattern.Offset)
assert.DeepEqual(t, code, pattern.Code)
}
}