https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115289
Bug ID: 115289
Summary: PPC: Document the machine constraint 'Y' and make it
non-internal
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: mpe+gcc at ellerman dot id.au
Target Milestone: ---
Please document the "Y" inline asm constraint for powerpc. It's needed to
correctly pass arbitrary pointer arguments to inline asm using a DS-form
instruction.
The Linux Kernel plans to use the constraint, see:
https://lore.kernel.org/linuxppc-dev/20240529123029.146953-1-...@ellerman.id.au/
A minimal reproducer for the problem seen in the kernel is below.
$ cat test.c
struct {
long a;
long b;
short c;
char d[8];
} e;
void f(void) {
unsigned long v = 0;
unsigned long *g = (unsigned long *)&e.d;
asm goto("std%X0 %1,%0 # put_user\n" : "=m"(*g) : "r"(v) : : out);
out:
}
$ gcc-14 -Wall -nostdinc -O2 -c -o test.o test.c
/tmp/ccsSkWJz.s: Assembler messages:
/tmp/ccsSkWJz.s:21: Error: operand out of domain (18 is not a multiple of 4)
