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[RFC] : Fix Ada boostrap failure on S/390 with -mzarch

Message ID 20170403142327.GA29110@maggie
State New
Headers show

Commit Message

Andreas Krebbel April 3, 2017, 2:23 p.m. UTC 
Hi Eric,

I ran into a similiar problem as PR80117 on S/390 starting with your
patch merging the system*.ads files for some biarch plattforms.
Starting with that change GCC does not bootstrap on S/390 when
configured with --with-mode=zarch.

On S/390 UNITS_PER_WORD is:
8 with -m64
4 with -m31
8 with -m31 -mzarch

This has been chosen to support use of 64 bit registers also in 32 bit
code.  Code compiled with -m31 -mzarch is supposed to adhere to the 32
bit ABI.  In order to make that work it was required to prevent
UNITS_PER_WORD from being used in ABI-relevant contexts.  That's why
Ulrich added the TARGET_UNWIND_WORD_MODE in 2008 (for SPU).

More target hooks were needed for UNITS_PER_WORD uses in libgcc:
TARGET_LIBGCC_CMP_RETURN_MODE, and TARGET_LIBGCC_SHIFT_COUNT_MODE.

The use of the UNITS_PER_WORD in the system.ads files looks like
adding another ABI/API-relevant use to me.

Now I could either fix this by reverting that change for S/390
(similiar to what Andreas Schwab did to fix the BZ) or I could just
use the size of the long data type (as we do in the ABI-relevant parts
of the backend as well).  Which one do you prefer?

Bye,

-Andreas-

Comments

Eric Botcazou April 3, 2017, 4:18 p.m. UTC | #1 
> On S/390 UNITS_PER_WORD is:
> 8 with -m64
> 4 with -m31
> 8 with -m31 -mzarch
> 
> This has been chosen to support use of 64 bit registers also in 32 bit
> code.  Code compiled with -m31 -mzarch is supposed to adhere to the 32
> bit ABI.  In order to make that work it was required to prevent
> UNITS_PER_WORD from being used in ABI-relevant contexts.  That's why
> Ulrich added the TARGET_UNWIND_WORD_MODE in 2008 (for SPU).

We do that for 32-bit SPARC on Solaris (-mv8plus) but UNITS_PER_WORD is 4.

> Now I could either fix this by reverting that change for S/390
> (similiar to what Andreas Schwab did to fix the BZ) or I could just
> use the size of the long data type (as we do in the ABI-relevant parts
> of the backend as well).  Which one do you prefer?

Having System.Word_Size != Standard'Word_Size is a bit disturbing.  Does it 
work to change only Memory_Size to 2 ** Long_Integer'Size?  This will also 
correct the definition of Address below.
diff mbox

Patch

diff --git a/gcc/ada/system-linux-s390.ads b/gcc/ada/system-linux-s390.ads
index 485a8de..144c46d 100644
--- a/gcc/ada/system-linux-s390.ads
+++ b/gcc/ada/system-linux-s390.ads
@@ -69,7 +69,7 @@  package System is
    Null_Address : constant Address;
 
    Storage_Unit : constant := 8;
-   Word_Size    : constant := Standard'Word_Size;
+   Word_Size    : constant := Long_Integer'Size;
    Memory_Size  : constant := 2 ** Word_Size;
 
    --  Address comparison