Date: Sun, 15 Sep 2013 21:29:29 GMT From: Robert Watson <rwatson@FreeBSD.org> To: Perforce Change Reviews <perforce@FreeBSD.org> Subject: PERFORCE change 719157 for review Message-ID: <201309152129.r8FLTThp072194@skunkworks.freebsd.org>
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http://p4web.freebsd.org/@@719157?ac=10 Change 719157 by rwatson@rwatson_zenith_cl_cam_ac_uk on 2013/09/15 21:28:53 Begin to flesh out the framing around a software CCall/CReturn path: branch from a low-level exception handler in the vector table to one of two higher-level paths: CHERICCall and CHERICReturn. Select the path based on the cause register. Many more assertions required here -- and this is still just an (increasingly complicated) NOP. Affected files ... .. //depot/projects/ctsrd/cheribsd/src/sys/mips/cheri/ccall.S#4 edit Differences ... ==== //depot/projects/ctsrd/cheribsd/src/sys/mips/cheri/ccall.S#4 (text+ko) ==== @@ -43,17 +43,80 @@ #include "assym.s" +/* + * Software implementations of CCall, CReturn handlers for CHERI. + * + * The low-level CHERICCallVector exception handler, which has been relocated + * to the MIPS exception vector table, jumps to either CHERICCall or + * CHERICReturn running in the normal kernel address space. + * + * Notice that 'j' is used, implying that the kernel is in the 32-bit kernel + * segment so that the target fits in the available immediate -- this is also + * true of other FreeBSD exception handlers. + */ + .set noreorder /* Preserve nops, allow instructions in b-d slots. */ /* - * Software implementations of CCall, CReturn handlers for CHERI. + * CCall/CReturn low-level exception handler; this code must be position- + * independent, as it will be relocated into the vector table. + */ +VECTOR(CHERICCallVector, unknown) + .set push + .set noat + CHERI_EXCEPTION_ENTER(k0) + + /* + * Determine whether this is a CCall or CReturn instruction. + * + * XXXRW: Panic if CGetCause returns something other than CALL/RETURN. + * + * XXXRW: Panic if not entering from userspace. + */ + CGetCause k0 + andi k0, k0, 0x1 /* CALL is odd; RETURN is even. */ + beqz k0, CReturn_label + nop /* Branch-delay slot. */ + + j CHERICCall + nop /* Branch-delay slot. */ + +CReturn_label: + j CHERICReturn + nop /* Branch-delay slot. */ + + .set pop +VECTOR_END(CHERICCallVector) + +/* + * Software implementation of CCall; this code does not need to be position- + * independent. + * + * XXXRW: Gubbins missing. + */ +CHERICCall: + .set push + .set noat + + /* XXXRW: For now, increment PC as though it were a no-op. */ + MFC0 k0, MIPS_COP_0_EXC_PC + PTR_ADDU k0, 4 + MTC0 k0, MIPS_COP_0_EXC_PC + COP0_SYNC + + CHERI_EXCEPTION_RETURN(k0) + eret + .set pop + +/* + * Software implementation of CReturn; this code does not need to be position- + * independent. * * XXXRW: Gubbins missing. */ -VECTOR(CHERICCallVector, unknown) +CHERICReturn: .set push .set noat - CHERI_EXCEPTION_ENTER(k0) /* XXXRW: For now, increment PC as though it were a no-op. */ MFC0 k0, MIPS_COP_0_EXC_PC @@ -64,4 +127,3 @@ CHERI_EXCEPTION_RETURN(k0) eret .set pop -VECTOR_END(CHERICCallVector)
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