On 18/05/2022 13.07, Janis Schoetterl-Glausch wrote:
On 5/17/22 18:09, Thomas Huth wrote:
On 17/05/2022 14.02, Claudio Imbrenda wrote:
On Mon, 16 May 2022 16:43:32 +0200
Janis Schoetterl-Glausch <scgl@xxxxxxxxxxxxx> wrote:
gcc 12 warns if a memory operand to inline asm points to memory in the
first 4k bytes. However, in our case, these operands are fine, either
because we actually want to use that memory, or expect and handle the
resulting exception.
Therefore, silence the warning.
I really dislike this
I agree the pragmas are ugly. But maybe we should mimic what the kernel
is doing here?
$ git show 8b202ee218395
commit 8b202ee218395319aec1ef44f72043e1fbaccdd6
Author: Sven Schnelle <svens@xxxxxxxxxxxxx>
Date: Mon Apr 25 14:17:42 2022 +0200
s390: disable -Warray-bounds
gcc-12 shows a lot of array bound warnings on s390. This is caused
by the S390_lowcore macro which uses a hardcoded address of 0.
Wrapping that with absolute_pointer() works, but gcc no longer knows
that a 12 bit displacement is sufficient to access lowcore. So it
emits instructions like 'lghi %r1,0; l %rx,xxx(%r1)' instead of a
single load/store instruction. As s390 stores variables often
read/written in lowcore, this is considered problematic. Therefore
disable -Warray-bounds on s390 for gcc-12 for the time being, until
there is a better solution.
... so we should maybe disable it in the Makefile, too, until the
kernel folks found a nicer solution?
Thomas
Neat, wasn't aware of that commit.
I don't think we need to concern ourselves with performance in this case and can define
+#define HIDE_PTR(ptr) \
+({ \
+ uint64_t __ptr; \
+ asm ("" : "=d" (__ptr) : "0" (ptr)); \
+ (typeof(ptr))__ptr; \
+})
+
in some header (which?).
Another alternative would be to define some extern symbols for the addresses we want to use.
It might be nice to have a symbol for the lowcore anyway, then we can get rid of
static struct lowcore *lc;
struct lowcore *lc = (struct lowcore *)0x0;
...
in a bunch of tests.
I like that idea.
And use that symbol to derive the addresses we want to use.
emulator.c uses -1 to generate an addressing exception, we either need another symbol for
that or use another invalid address. (Can't get to -1 from lowcore/0 because the max array
size is signed int64 max)
Maybe use INT64_MAX or something similar? Would that work?
Thomas
