[PATCH] Semihosting ctr0 typo (adr/ldr)?

[Richard Earnshaw]

On 17/02/2021 10:01, Corinna Vinschen wrote:
> On Feb 16 22:56, iNvEr7 via Newlib wrote:
>>
>> ---
>>  libgloss/arm/crt0.S        | 2 +-
>>  newlib/libc/sys/arm/crt0.S | 2 +-
>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/libgloss/arm/crt0.S b/libgloss/arm/crt0.S
>> index 8490bde2f..b8bbcee18 100644
>> --- a/libgloss/arm/crt0.S
>> +++ b/libgloss/arm/crt0.S
>> @@ -283,7 +283,7 @@
>>  #ifdef ARM_RDI_MONITOR
>>  	/*  Issue Angel SWI to read stack info.  */
>>  	movs	r0, #AngelSWI_Reason_HeapInfo
>> -	adr	r1, .LC0	/*  Point at ptr to 4 words to receive data.  */
>> +	ldr	r1, .LC0	/*  Point at ptr to 4 words to receive data.  */
>>  #ifdef THUMB_VXM
>>  	bkpt	AngelSWI
>>  #elif defined(__thumb2__)
>> diff --git a/newlib/libc/sys/arm/crt0.S b/newlib/libc/sys/arm/crt0.S
>> index 5e677a23c..3c5771229 100644
>> --- a/newlib/libc/sys/arm/crt0.S
>> +++ b/newlib/libc/sys/arm/crt0.S
>> @@ -270,7 +270,7 @@
>>  #ifdef ARM_RDI_MONITOR
>>  	/*  Issue Angel SWI to read stack info.  */
>>  	movs	r0, #AngelSWI_Reason_HeapInfo
>> -	adr	r1, .LC0	/*  Point at ptr to 4 words to receive data.  */
>> +	ldr	r1, .LC0	/*  Point at ptr to 4 words to receive data.  */
>>  #ifdef THUMB_VXM
>>  	bkpt	AngelSWI
>>  #elif defined(__thumb2__)
>> --
>> 2.29.2
> 
> I'm a bit suprised that this problem hasn't been noticed for the
> last 10 years.  I'm not familiar with the ARM stuff at all, so maybe
> somebody from ARM can chime in here?
> 
> 
> Thanks,
> Corinna
> 

No, I don't think that is right, but it took some digging to be sure.

The specification for the HeapInfo syscall is here:

https://developer.arm.com/documentation/100863/0300/Semihosting-operations/SYS-HEAPINFO--0x16-?lang=en

and it says that the parameter is the /address of a pointer/ to the
4-word block.  In other words, it is not the address of the block itself.

It's odd that it is defined this way, but I think the code is doing what
the specification says.  Certainly the comments in the code seem to
reflect this.

R.