https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127165
Bug ID: 127165
Summary: asm() limited to 30 arguments
Product: gcc
Version: 16.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: andrew.cooper3 at citrix dot com
Target Milestone: ---
The following logic is necessary to make a PSCI v1.2 compliant SMC call on
Aarch64 using inline assembly:
-----
struct psci_args {
unsigned long
x0, x1, x2, x3, x4, x5, x6, x7, x8,
x9, x10, x11, x12, x13, x14, x15, x16, x17;
};
void psci_1_2(struct psci_args *regs)
{
register unsigned long r0 asm("x0") = regs->x0;
register unsigned long r1 asm("x1") = regs->x1;
register unsigned long r2 asm("x2") = regs->x2;
register unsigned long r3 asm("x3") = regs->x3;
register unsigned long r4 asm("x4") = regs->x4;
register unsigned long r5 asm("x5") = regs->x5;
register unsigned long r6 asm("x6") = regs->x6;
register unsigned long r7 asm("x7") = regs->x7;
register unsigned long r8 asm("x8") = regs->x8;
register unsigned long r9 asm("x9") = regs->x9;
register unsigned long r10 asm("x10") = regs->x10;
register unsigned long r11 asm("x11") = regs->x11;
register unsigned long r12 asm("x12") = regs->x12;
register unsigned long r13 asm("x13") = regs->x13;
register unsigned long r14 asm("x14") = regs->x14;
register unsigned long r15 asm("x15") = regs->x15;
register unsigned long r16 asm("x16") = regs->x16;
register unsigned long r17 asm("x17") = regs->x17;
asm volatile (
"smc #0"
: "+r" (r0), "+r" (r1), "+r" (r2), "+r" (r3),
"+r" (r4), "+r" (r5), "+r" (r6), "+r" (r7),
"+r" (r8), "+r" (r9), "+r" (r10), "+r" (r11),
"+r" (r12), "+r" (r13), "+r" (r14), "+r" (r15),
"+r" (r16), "+r" (r17)
:
: "memory" );
regs->x0 = r0;
regs->x1 = r1;
regs->x2 = r2;
regs->x3 = r3;
regs->x4 = r4;
regs->x5 = r5;
regs->x6 = r6;
regs->x7 = r7;
regs->x8 = r8;
regs->x9 = r9;
regs->x10 = r10;
regs->x11 = r11;
regs->x12 = r12;
regs->x13 = r13;
regs->x14 = r14;
regs->x15 = r15;
regs->x16 = r16;
regs->x17 = r17;
}
-----
yet trying to compile it fails with:
<source>: In function 'psci_1_2':
<source>:28:5: error: more than 30 operands in 'asm'
28 | asm volatile (
| ^~~
Compiler returned: 1
Full Godbolt example: https://godbolt.org/z/Wj33abKvE
Clang can compile this just fine, and the limit of 30 arguments for an asm()
seems arbitrary, and isn't sufficient for architectures with 32 registers.
Is there anything stopping the limit being higher?
