This changes allows a test to define and override the declared symbols,
taking control of all or some execptions.
With the ability to override specific exception handlers, litmus7 [1] a
tool used to generate c sources for a given memory model litmus test,
can override the el1h_sync symbol to implement tests with explicit
exception handlers. For example:
AArch64 LDRv0+I2V-dsb.ishst-once
{
[PTE(x)]=(oa:PA(x),valid:0);
x=1;
0:X1=x;
0:X3=PTE(x);
0:X2=(oa:PA(x),valid:1);
}
P0 | P0.F ;
L0: | ADD X8,X8,#1 ;
LDR W0,[X1] | STR X2,[X3] ;
| DSB ISHST ;
| ADR X9,L0 ;
| MSR ELR_EL1,X9 ;
| ERET ;
exists(0:X0=0 \/ 0:X8!=1)
In this test, a thread running in core P0 executes a load to a memory
location x. The PTE of the virtual address x is initially invalid. The
execution of the load causes a synchronous EL1 exception which is
handled by the code in P0.F. P0.F increments a counter which is
maintained in X8, updates the PTE of x and makes it valid, executes a
DSB ISHST and calls ERET which is expected to return and retry the
execution of the load in P0:L0.
The postcondition checks if there is any execution where the load wasn't
executed (X0 its destination register is not update), or that the P0.F
handler was invoked more than once (the counter X8 is not 1).
For this tests, litmus7 needs to control the el1h_sync. Calling
install_exception_handler() would be suboptimal because the
vector_stub would wrap around the code of P0.F and perturb the test.
[1]: https://diy.inria.fr/doc/litmus.html
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@xxxxxxx>
---
arm/cstart64.S | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/arm/cstart64.S b/arm/cstart64.S
index e4ab7d06..eda0daa5 100644
--- a/arm/cstart64.S
+++ b/arm/cstart64.S
@@ -275,8 +275,11 @@ exceptions_init:
/*
* Vector stubs
* Adapted from arch/arm64/kernel/entry.S
+ * Declare as weak to allow external tests to redefine and override a
+ * vector_stub.
*/
.macro vector_stub, name, vec
+.weak \name
\name:
stp x0, x1, [sp, #-S_FRAME_SIZE]!
stp x2, x3, [sp, #16]
@@ -369,7 +372,13 @@ vector_stub el0_error_32, 15
b \label
.endm
+
+/*
+ * Declare as weak to allow external tests to redefine and override the
+ * default vector table.
+ */
.align 11
+.weak vector_table
vector_table:
ventry el1t_sync // Synchronous EL1t
ventry el1t_irq // IRQ EL1t
--
2.25.1
