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Loongarch relative branches immediate value inconsistent with other architectures #2689

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OBarronCS opened this issue Apr 23, 2025 · 2 comments · Fixed by #2699
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Loongarch relative branches immediate value inconsistent with other architectures #2689

OBarronCS opened this issue Apr 23, 2025 · 2 comments · Fixed by #2699
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bug Something is not working as it should LoongArch Arch

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@OBarronCS
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Capstone module affected Loongarch32 and Loongarch64
Source of Capstone pip install capstone==6.0.0a4
Version/git commit 6.0.0 alpha 4

Relative branches in Loongarch do not add the value of the immediate to the instruction address so that the target address is encoded in .imm, as occurs in other instructions.

Actual behavior

cstool -d loongarch64 "80 0d 00 40 " 0x1000
1000  80 0d 00 40  beqz	$t0, 0xc
	ID: 117 (beqz)
	op_count: 2
		operands[0].type: REG = t0
		operands[0].access: READ
		operands[1].type: IMM = 0xc
		operands[1].access: READ
	Registers read: t0
	Groups: jump branch_relative 


cstool -d loongarch64 "00 ec 0b 54" 0x1000
1000  00 ec 0b 54  bl	0xbec
	ID: 124 (bl)
	op_count: 1
		operands[0].type: IMM = 0xbec
		operands[0].access: READ
	Registers modified: ra
	Groups: call

Expected behavior

The expected behavior would be for the instruction address (the value 0x1000 above) to be added to the immediate, so that the immediate contains the target address, as occurs in other architectures.

An example je instruction in x86-64:

cstool -d x64 "74 4a"  0x1000
1000  74 4a                                            je	0x104c
	ID: 260 (je)
	Prefix:0x00 0x00 0x00 0x00 
	Opcode:0x74 0x00 0x00 0x00 
	rex: 0x0
	addr_size: 8
	modrm: 0x0
	disp: 0x0
	sib: 0x0
	imm_count: 1
		imms[1]: 0x104c
	op_count: 1
		operands[0].type: IMM = 0x104c
		operands[0].size: 8
	Registers read: rflags
	Registers modified: eip
	EFLAGS: TEST_ZF
	Groups: branch_relative jump

In this example, the constant offset 0x4c is added to the offset 0x1000 so that the branch target is encoded in the .imm value, 0x104c.
@Rot127 Rot127 added bug Something is not working as it should LoongArch Arch labels Apr 24, 2025
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Rot127 commented Apr 24, 2025

cc @jiegec

jiegec added a commit to jiegec/capstone that referenced this issue May 7, 2025
@jiegec
LoongArch: Compute absolute address for address operand
a76841b 
To match behavior with other archs, compute absolute address instead of
relative for address operands. Fixes capstone-engine#2689.
@jiegec jiegec mentioned this issue May 7, 2025
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@jiegec
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jiegec commented May 7, 2025

Fix proposed #2699

jiegec added a commit to jiegec/capstone that referenced this issue May 9, 2025
@jiegec
LoongArch: Compute absolute address for address operand
e993302 
To match behavior with other archs, compute absolute address instead of
relative for address operands. Fixes capstone-engine#2689.
kabeor pushed a commit that referenced this issue May 20, 2025
@jiegec
LoongArch: Compute absolute address for address operand (#2699)
829be2b 
To match behavior with other archs, compute absolute address instead of
relative for address operands. Fixes #2689.
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LoongArch: Compute absolute address for address operand jiegec/capstone
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@jiegec @Rot127 @OBarronCS