| Message ID | 1461086788-3102-3-git-send-email-lvivier@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 19 Apr 2016 19:26:28 +0200 Laurent Vivier <lvivier@redhat.com> wrote: > As the TOC pointer can be corrupted by the main program, > we must restore it in the exception handler. > > As we know where we are loaded, we can now compute it easily. > > To compute it only in the common part of the exception handler > (call_handler), store the address of call_handler at an absolute > address in memory to be able to call the handler from the exception > table (as SLOF does). > > Reported-by: Thomas Huth <thuth@redhat.com> > Signed-off-by: Laurent Vivier <lvivier@redhat.com> So, this looks ok as long as the unit tests are built with a single TOC. The more stricly correct approach would be to actually load the correct TOC pointer for the specific handler function you're going to jump to. That would need different paths for ABIv1 and v2, though (in practice ppc64 vs. ppc64le). With ABIv1 (ppc64) you'd need to load the TOC pointer from the procedure descriptor into r2 before jumping to the code address. With ABIv2 (ppc64le), I believe there's both a "far" and "near" entry point to the function - the "far" one has a few instructions to load the correct TOC before continuing onto the "near" version. I forget which entry point the plain symbol references. If it's the "far" one, the current code is probably already correct. > --- > powerpc/cstart64.S | 17 ++++++++++++++++- > 1 file changed, 16 insertions(+), 1 deletion(-) > > diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S > index c47b67d..1ddfa13 100644 > --- a/powerpc/cstart64.S > +++ b/powerpc/cstart64.S > @@ -13,6 +13,8 @@ > > #include "spapr.h" > > +#define P_HANDLER 0x2ff8 > + > .section .init > > /* > @@ -46,6 +48,11 @@ start: > add r4, r4, r31 > bl relocate > > + /* compute address of call_handler */ > + > + LOAD_REG_ADDR(r4, call_handler) > + std r4, P_HANDLER(0) > + > /* relocate vector table to base address 0x0 (MSR_IP = 0) */ > > /* source: r4, dest end: r5, destination: r6 */ > @@ -166,6 +173,12 @@ call_handler: > mfsrr1 r0 > std r0, _MSR(r1) > > + /* restore TOC pointer */ > + > + LOAD_REG_IMMEDIATE(r31, SPAPR_KERNEL_LOAD_ADDR) > + ld r2, (p_toc - start)(r31) > + add r2, r2, r31 > + > /* FIXME: build stack frame */ > > /* call generic handler */ > @@ -221,7 +234,7 @@ call_handler: > mfctr r0 > std r0,_CTR(r1) > > - LOAD_REG_ADDR(r0, call_handler) > + ld r0, P_HANDLER(0) > mtctr r0 > > li r0,\vec > @@ -245,3 +258,5 @@ VECTOR(0x900) > .align 7 > .globl __end_interrupts > __end_interrupts: > + .org P_HANDLER > + .llong 0 > -- > 2.5.5 >
On 20.04.2016 07:59, David Gibson wrote: > On Tue, 19 Apr 2016 19:26:28 +0200 > Laurent Vivier <lvivier@redhat.com> wrote: > >> As the TOC pointer can be corrupted by the main program, >> we must restore it in the exception handler. >> >> As we know where we are loaded, we can now compute it easily. >> >> To compute it only in the common part of the exception handler >> (call_handler), store the address of call_handler at an absolute >> address in memory to be able to call the handler from the exception >> table (as SLOF does). >> >> Reported-by: Thomas Huth <thuth@redhat.com> >> Signed-off-by: Laurent Vivier <lvivier@redhat.com> > > So, this looks ok as long as the unit tests are built with a single > TOC. In case there would be multiple TOCs, the previous exception handler would not work at all anymore, since it does not set up r2 at all. So for the current scope of kvm-unit-tests, I think this here is already enough - we can still extend it later in case we ever need to support multiple TOCs. So to me, this patch looks fine: Reviewed-by: Thomas Huth <thuth@redhat.com>
diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S index c47b67d..1ddfa13 100644 --- a/powerpc/cstart64.S +++ b/powerpc/cstart64.S @@ -13,6 +13,8 @@ #include "spapr.h" +#define P_HANDLER 0x2ff8 + .section .init /* @@ -46,6 +48,11 @@ start: add r4, r4, r31 bl relocate + /* compute address of call_handler */ + + LOAD_REG_ADDR(r4, call_handler) + std r4, P_HANDLER(0) + /* relocate vector table to base address 0x0 (MSR_IP = 0) */ /* source: r4, dest end: r5, destination: r6 */ @@ -166,6 +173,12 @@ call_handler: mfsrr1 r0 std r0, _MSR(r1) + /* restore TOC pointer */ + + LOAD_REG_IMMEDIATE(r31, SPAPR_KERNEL_LOAD_ADDR) + ld r2, (p_toc - start)(r31) + add r2, r2, r31 + /* FIXME: build stack frame */ /* call generic handler */ @@ -221,7 +234,7 @@ call_handler: mfctr r0 std r0,_CTR(r1) - LOAD_REG_ADDR(r0, call_handler) + ld r0, P_HANDLER(0) mtctr r0 li r0,\vec @@ -245,3 +258,5 @@ VECTOR(0x900) .align 7 .globl __end_interrupts __end_interrupts: + .org P_HANDLER + .llong 0
As the TOC pointer can be corrupted by the main program, we must restore it in the exception handler. As we know where we are loaded, we can now compute it easily. To compute it only in the common part of the exception handler (call_handler), store the address of call_handler at an absolute address in memory to be able to call the handler from the exception table (as SLOF does). Reported-by: Thomas Huth <thuth@redhat.com> Signed-off-by: Laurent Vivier <lvivier@redhat.com> --- powerpc/cstart64.S | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)