[PATCH] elf: Fix rtld-audit trampoline for aarch64

[Vladislav Khmelevsky]

Thank you for reviewing!
Yes, it is true tat inly x0/x1 are used as return register. But I have a specific audit library code that was storing some metadata in a free registers during plt entrer and reading it during plt exit :) As for a normal use cases both problems doesn't really affect anything.

> 17 нояб. 2022 г., в 22:15, Adhemerval Zanella Netto <adhemerval.zanella@linaro.org> написал(а):
> 
> 
> 
> On 17/11/22 05:47, Vladislav Khmelevsky wrote:
>> This patch fixes two problems with audit:
>> 1. The DL_OFFSET_RV_VPCS offset was mixed up with DL_OFFSET_RG_VPCS,
>> resulting in x2 register value nulling in RG structure.
>> 2. We need to preserve the x8 register before function call, but don't have
>> to save it's new value and restore it before return. Anyway the final
>> restore was using OFFSET_RV instead of OFFSET_RG value which is wrong (althoug doesn't affect anything).
> 
> Patch looks ok, although I think currently the ABI only uses x0 and/or x1
> to return value (for __int128_t for instance). So I think it should not
> be a user-visible issue (at least tst-audit26 does check that lr_vpcs
> and lrv_vpcs are zeroed). Are you seeing any issue with current code?
> If so could you open a bug please?
> 
>> ---
>> sysdeps/aarch64/dl-trampoline.S | 4 +---
>> 1 file changed, 1 insertion(+), 3 deletions(-)
>> 
>> diff --git a/sysdeps/aarch64/dl-trampoline.S b/sysdeps/aarch64/dl-trampoline.S
>> index 909b208578..d66f0b9c45 100644
>> --- a/sysdeps/aarch64/dl-trampoline.S
>> +++ b/sysdeps/aarch64/dl-trampoline.S
>> @@ -298,12 +298,11 @@ _dl_runtime_profile:
>> 	stp	x2, x3, [x29, #OFFSET_RV + DL_OFFSET_RV_X0 + 16*1]
>> 	stp	x4, x5, [x29, #OFFSET_RV + DL_OFFSET_RV_X0 + 16*2]
>> 	stp	x6, x7, [x29, #OFFSET_RV + DL_OFFSET_RV_X0 + 16*3]
>> -	str	x8,     [x29, #OFFSET_RG + DL_OFFSET_RG_X0 + 16*4]
>> 	stp	q0, q1, [x29, #OFFSET_RV + DL_OFFSET_RV_V0 + 32*0]
>> 	stp	q2, q3, [x29, #OFFSET_RV + DL_OFFSET_RV_V0 + 32*1]
>> 	stp	q4, q5, [x29, #OFFSET_RV + DL_OFFSET_RV_V0 + 32*2]
>> 	stp	q6, q7, [x29, #OFFSET_RV + DL_OFFSET_RV_V0 + 32*3]
>> -	str	xzr,    [X29, #OFFSET_RV + DL_OFFSET_RG_VPCS]
>> +	str	xzr,    [X29, #OFFSET_RV + DL_OFFSET_RV_VPCS]
>> 
>> 	/* Setup call to pltexit  */
>> 	ldp	x0, x1, [x29, #OFFSET_SAVED_CALL_X0]
>> @@ -315,7 +314,6 @@ _dl_runtime_profile:
>> 	ldp	x2, x3, [x29, #OFFSET_RV + DL_OFFSET_RV_X0 + 16*1]
>> 	ldp	x4, x5, [x29, #OFFSET_RV + DL_OFFSET_RV_X0 + 16*2]
>> 	ldp	x6, x7, [x29, #OFFSET_RV + DL_OFFSET_RV_X0 + 16*3]
>> -	ldr	x8,     [x29, #OFFSET_RV + DL_OFFSET_RV_X0 + 16*4]
>> 	ldp	q0, q1, [x29, #OFFSET_RV + DL_OFFSET_RV_V0 + 32*0]
>> 	ldp	q2, q3, [x29, #OFFSET_RV + DL_OFFSET_RV_V0 + 32*1]
>> 	ldp	q4, q5, [x29, #OFFSET_RV + DL_OFFSET_RV_V0 + 32*2]