[PATCH v6 10/13] ARC: ABI lists

Vineet Gupta Vineet.Gupta1@synopsys.com
Fri Jun 5 02:22:52 GMT 2020


On 6/3/20 12:29 PM, Adhemerval Zanella via Libc-alpha wrote:
> 
> 
> On 22/04/2020 22:41, Vineet Gupta via Libc-alpha wrote:
>> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
> 
> LGTM with a just isseu regarding the pulled memcpy from libgcc.

Just to be clear

This is libgcc routine calling memcpy from gcc and libgcc-static linked into libc
pulling in this PLT. And this is only for soft float + Os.  And there's just this
one instance in libc which uses PLT, all other internal memcpy calls are direct.

$ arc-linux-objdump -d lib/libc-2.31.9000.so

0001b014 <.plt>:
...
   1b0e4:	ld	r12,[pcl,0xe6f50] ;102034 <memcpy@@GLIBC_2.32+0x9b020>
   1b0ec:	j.d	[r12]
   1b0f0:	mov	r12,pcl

000d0fd8 <_fpadd_parts>:
...
   d17ba:	bl	1b0e4 <.plt+0xd0>	<-- memcpy via PLT


000655a4 <__libc_alloc_buffer_copy_bytes>:
...
   655c4:	bl.d	6736	;67014 <memcpy>
...

00067014 <memcpy>:
   67014:	push_s	blink
...

>> diff --git a/sysdeps/unix/sysv/linux/arc/localplt.data b/sysdeps/unix/sysv/linux/arc/localplt.data
>> new file mode 100644
>> index 000000000000..4479e8ee8a26
>> --- /dev/null
>> +++ b/sysdeps/unix/sysv/linux/arc/localplt.data
>> @@ -0,0 +1,12 @@
>> +libc.so: realloc
>> +libc.so: malloc
>> +libc.so: memalign
>> +libc.so: calloc
>> +libc.so: free
>> +# At -Os, a struct assignment in libgcc-static pulls this in
>> +libc.so: memcpy ?

> This is mosty likely an issue 

Care to elaborate what the issue is exactly: that memcpy being local to libc dso
is still routed via PLT ? Or that the entry is only present sometimes ?


> and we handle this issue with an
> assembly hack to redirect the autogenerate memcpy/memmove calls
> to internal definitions (sysdeps/generic/symbol-hacks.h).
> 
> I am not sure exactly if this would be avoided in ARC configuration,
> maybe it could adapt the sparc32 hack for the libgcc .udiv symbol
> (sysdeps/sparc/sparc32/Makefile).

I looked at the code and this seems different than our issue.


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