Re: [PATCH v3 03/21] perf llvm: Fix arm64 adrp instruction disassembly mismatch with objdump

[Tengda Wu]

On 2026/7/9 15:49, Tengda Wu wrote:
> 
> 
> On 2026/7/9 14:18, Namhyung Kim wrote:
>> On Wed, Jul 01, 2026 at 03:53:37AM +0000, Tengda Wu wrote:
>>> The operands of 'adrp' instructions parsed by libllvm are currently
>>> represented as raw immediates rather than the "address <symbol+offset>"
>>> format used by objdump. This inconsistency causes arm64_mov__parse()
>>> to fail when parsing these instructions during post-processing.
>>>
>>> Example of the mismatch:
>>>   Current: adrp x18, 8014
>>>   Fix:     adrp x18, ffff800081f5f000 <this_cpu_vector>
>>>
>>> Fix this by manually extracting the target address from the raw adrp
>>> instruction via symbol_lookup_callback(). The address is then converted
>>> to a specific symbol during symbol__disassemble_llvm() and formatted
>>> to match objdump's output, ensuring compatibility with existing
>>> parsers.
>>>
>>> Signed-off-by: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
>>> ---
>>>  tools/perf/util/llvm.c | 50 ++++++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 50 insertions(+)
>>>
>>> diff --git a/tools/perf/util/llvm.c b/tools/perf/util/llvm.c
>>> index a0deb742a733..533d47e8084d 100644
>>> --- a/tools/perf/util/llvm.c
>>> +++ b/tools/perf/util/llvm.c
>>> @@ -94,6 +94,7 @@ static void init_llvm(void)
>>>  struct symbol_lookup_storage {
>>>  	u64 branch_addr;
>>>  	u64 pcrel_load_addr;
>>> +	u64 pcrel_adrp_addr;
>>>  };
>>>  
>>>  static const char *
>>> @@ -108,6 +109,18 @@ symbol_lookup_callback(void *disinfo, uint64_t value,
>>>  		storage->branch_addr = value;
>>>  	else if (*ref_type == LLVMDisassembler_ReferenceType_In_PCrel_Load)
>>>  		storage->pcrel_load_addr = value;
>>
>> Is this used by arm64?  If not, would be possible to reuse
>> pcrel_load_addr unless it'd complicate the code significantly?
>>
>> I think it's the common concept of PC-relative addressing while it
>> requires two instructions to set up the final address on arm64.
>>
>> Thanks,
>> Namhyung
>>

I checked the LLVM internal implementation and conducted further experiments.
You are correct, arm64 does not trigger LLVMDisassembler_ReferenceType_In_PCrel_Load
at all. Instead, it utilizes its own architecture-specific reference types
like LLVMDisassembler_ReferenceType_In_ARM64_ADRP, _LDRXl, etc.
Therefore, 'pcrel_load_addr' is completely safe to reuse here.

I will reuse 'pcrel_load_addr' to avoid adding unnecessary fields and
optimize this patch in the next version.

Thanks,
Tengda

> 
>>> +	else if (*ref_type == LLVMDisassembler_ReferenceType_In_ARM64_ADRP) {
>>> +		uint64_t adrp_imm;
>>> +
>>> +		/* immhi (bits 23:5) and immlo (bits 30:29) */
>>> +		adrp_imm = ((value & 0x00ffffe0) >> 3) | ((value >> 29) & 0x3);
>>> +		/* Sign-extend the 21-bit immediate to 64-bit */
>>> +		if (adrp_imm & (1ULL << 20))
>>> +			adrp_imm |= ~((1ULL << 21) - 1);
>>> +
>>> +		/* Calculate the target page address */
>>> +		storage->pcrel_adrp_addr = (address & ~0xFFFLL) + (adrp_imm << 12);
>>> +	}
>>>  	*ref_type = LLVMDisassembler_ReferenceType_InOut_None;
>>>  	return NULL;
>>>  }
>>> @@ -204,6 +217,7 @@ int symbol__disassemble_llvm(const char *filename, struct symbol *sym,
>>>  
>>>  		storage.branch_addr = 0;
>>>  		storage.pcrel_load_addr = 0;
>>> +		storage.pcrel_adrp_addr = 0;
>>>  
>>>  		/*
>>>  		 * LLVM's API has the code be disassembled as non-const, cast
>>> @@ -227,6 +241,42 @@ int symbol__disassemble_llvm(const char *filename, struct symbol *sym,
>>>  				free(name);
>>>  			}
>>>  		}
>>> +		if (storage.pcrel_adrp_addr != 0) {
>>> +			/*
>>> +			 * ADRP (Address Page) instructions encode a 21-bit signed
>>> +			 * immediate offset relative to the current PC's page.
>>> +			 *
>>> +			 * To maintain consistency with standard objdump output,
>>> +			 * we truncate the raw encoded immediate at the comma
>>> +			 * and replace it with the resolved absolute page address.
>>> +			 *
>>> +			 * Example conversion:
>>> +			 * From: adrp x18, 8014
>>> +			 * To:   adrp x18, ffff800081f5f000 <this_cpu_vector>
>>> +			 */
>>> +			char *name;
>>> +			char *s = strchr(disasm_buf, ',');
>>> +
>>> +			if (s == NULL)
>>> +				goto err;
>>> +
>>> +			s++;
>>> +			*s = '\0';
>>> +			disasm_len = strlen(disasm_buf);
>>> +			disasm_len += scnprintf(disasm_buf + disasm_len,
>>> +						sizeof(disasm_buf) - disasm_len,
>>> +						" %"PRIx64,
>>> +						storage.pcrel_adrp_addr);
>>> +			name = llvm_name_for_data(dso, filename,
>>> +						  storage.pcrel_adrp_addr);
>>> +			if (name) {
>>> +				disasm_len += scnprintf(disasm_buf + disasm_len,
>>> +							sizeof(disasm_buf) -
>>> +							disasm_len,
>>> +							" <%s>", name);
>>> +				free(name);
>>> +			}
>>> +		}
>>>  		if (storage.pcrel_load_addr != 0) {
>>>  			char *name = llvm_name_for_data(dso, filename,
>>>  							storage.pcrel_load_addr);
>>> -- 
>>> 2.34.1
>>>