powerpc: Use gas sections for arranging exception vectors

Use assembler sections of fixed size and location to arrange the 64-bit
Book3S exception vector code (64-bit Book3E also uses it in head_64.S
for 0x0..0x100).

This allows better flexibility in arranging exception code and hiding
unimportant details behind macros.

Gas sections can be a bit painful to use this way, mainly because the
assembler does not know where they will be finally linked. Taking
absolute addresses requires a bit of trickery for example, but it can
be hidden behind macros for the most part.

Generated code is mostly the same except locations, offsets, alignments.

The "+ 0x2" is only required for the trap number / kvm exit number,
which gets loaded as a constant into a register.

Previously, code also used + 0x2 for label names, but we changed to
using "H" to distinguish HV case for that. Remove the last vestiges
of that.

__after_prom_start is taking absolute address of a label in another
fixed section. Newer toolchains seemed to compile this okay, but older
ones do not. FIXED_SYMBOL_ABS_ADDR is more foolproof, it just takes an
additional line to define.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 245 insertions, 16 deletions

diff --git a/arch/powerpc/include/asm/head-64.h b/arch/powerpc/include/asm/head-64.h
index 613f743e91aa..ab90c2fa1ea6 100644
--- a/arch/powerpc/include/asm/head-64.h
+++ b/arch/powerpc/include/asm/head-64.h
@@ -3,28 +3,218 @@
 
 #include <asm/cache.h>
 
+/*
+ * We can't do CPP stringification and concatination directly into the section
+ * name for some reason, so these macros can do it for us.
+ */
+.macro define_ftsec name
+	.section ".head.text.\name\()","ax",@progbits
+.endm
+.macro define_data_ftsec name
+	.section ".head.data.\name\()","a",@progbits
+.endm
+.macro use_ftsec name
+	.section ".head.text.\name\()"
+.endm
+
+/*
+ * Fixed (location) sections are used by opening fixed sections and emitting
+ * fixed section entries into them before closing them. Multiple fixed sections
+ * can be open at any time.
+ *
+ * Each fixed section created in a .S file must have corresponding linkage
+ * directives including location, added to  arch/powerpc/kernel/vmlinux.lds.S
+ *
+ * For each fixed section, code is generated into it in the order which it
+ * appears in the source.  Fixed section entries can be placed at a fixed
+ * location within the section using _LOCATION postifx variants. These must
+ * be ordered according to their relative placements within the section.
+ *
+ * OPEN_FIXED_SECTION(section_name, start_address, end_address)
+ * FIXED_SECTION_ENTRY_BEGIN(section_name, label1)
+ *
+ * USE_FIXED_SECTION(section_name)
+ * label3:
+ *     li  r10,128
+ *     mv  r11,r10
+
+ * FIXED_SECTION_ENTRY_BEGIN_LOCATION(section_name, label2, start_address)
+ * FIXED_SECTION_ENTRY_END_LOCATION(section_name, label2, end_address)
+ * CLOSE_FIXED_SECTION(section_name)
+ *
+ * ZERO_FIXED_SECTION can be used to emit zeroed data.
+ *
+ * Troubleshooting:
+ * - If the build dies with "Error: attempt to move .org backwards" at
+ *   CLOSE_FIXED_SECTION() or elsewhere, there may be something
+ *   unexpected being added there. Remove the '. = x_len' line, rebuild, and
+ *   check what is pushing the section down.
+ * - If the build dies in linking, check arch/powerpc/kernel/vmlinux.lds.S
+ *   for instructions.
+ * - If the kernel crashes or hangs in very early boot, it could be linker
+ *   stubs at the start of the main text.
+ */
+
+#define OPEN_FIXED_SECTION(sname, start, end)			\
+	sname##_start = (start);				\
+	sname##_end = (end);					\
+	sname##_len = (end) - (start);				\
+	define_ftsec sname;					\
+	. = 0x0;						\
+start_##sname:
+
+#define OPEN_TEXT_SECTION(start)				\
+	text_start = (start);					\
+	.section ".text","ax",@progbits;			\
+	. = 0x0;						\
+start_text:
+
+#define ZERO_FIXED_SECTION(sname, start, end)			\
+	sname##_start = (start);				\
+	sname##_end = (end);					\
+	sname##_len = (end) - (start);				\
+	define_data_ftsec sname;				\
+	. = 0x0;						\
+	. = sname##_len;
+
+#define USE_FIXED_SECTION(sname)				\
+	fs_label = start_##sname;				\
+	fs_start = sname##_start;				\
+	use_ftsec sname;
+
+#define USE_TEXT_SECTION()					\
+	fs_label = start_text;					\
+	fs_start = text_start;					\
+	.text
+
+#define CLOSE_FIXED_SECTION(sname)				\
+	USE_FIXED_SECTION(sname);				\
+	. = sname##_len;					\
+end_##sname:
+
+
+#define __FIXED_SECTION_ENTRY_BEGIN(sname, name, __align)	\
+	USE_FIXED_SECTION(sname);				\
+	.align __align;						\
+	.global name;						\
+name:
+
+#define FIXED_SECTION_ENTRY_BEGIN(sname, name)			\
+	__FIXED_SECTION_ENTRY_BEGIN(sname, name, 0)
+
+#define FIXED_SECTION_ENTRY_BEGIN_LOCATION(sname, name, start)		\
+	USE_FIXED_SECTION(sname);				\
+	name##_start = (start);					\
+	.if (start) < sname##_start;				\
+	.error "Fixed section underflow";			\
+	.abort;							\
+	.endif;							\
+	. = (start) - sname##_start;				\
+	.global name;						\
+name:
+
+#define FIXED_SECTION_ENTRY_END_LOCATION(sname, name, end)		\
+	.if (end) > sname##_end;				\
+	.error "Fixed section overflow";			\
+	.abort;							\
+	.endif;							\
+	.if (. - name > end - name##_start);			\
+	.error "Fixed entry overflow";				\
+	.abort;							\
+	.endif;							\
+	. = ((end) - sname##_start);				\
+
+
+/*
+ * These macros are used to change symbols in other fixed sections to be
+ * absolute or related to our current fixed section.
+ *
+ * - DEFINE_FIXED_SYMBOL / FIXED_SYMBOL_ABS_ADDR is used to find the
+ *   absolute address of a symbol within a fixed section, from any section.
+ *
+ * - ABS_ADDR is used to find the absolute address of any symbol, from within
+ *   a fixed section.
+ */
+#define DEFINE_FIXED_SYMBOL(label)				\
+	label##_absolute = (label - fs_label + fs_start)
+
+#define FIXED_SYMBOL_ABS_ADDR(label)				\
+	(label##_absolute)
+
+#define ABS_ADDR(label) (label - fs_label + fs_start)
+
+/*
+ * Following are the BOOK3S exception handler helper macros.
+ * Handlers come in a number of types, and each type has a number of varieties.
+ *
+ * EXC_REAL_*        - real, unrelocated exception vectors
+ * EXC_VIRT_*        - virt (AIL), unrelocated exception vectors
+ * TRAMP_REAL_*   - real, unrelocated helpers (virt can call these)
+ * TRAMP_VIRT_*  - virt, unreloc helpers (in practice, real can use)
+ * TRAMP_KVM         - KVM handlers that get put into real, unrelocated
+ * EXC_COMMON_*  - virt, relocated common handlers
+ *
+ * The EXC handlers are given a name, and branch to name_common, or the
+ * appropriate KVM or masking function. Vector handler verieties are as
+ * follows:
+ *
+ * EXC_{REAL|VIRT}_BEGIN/END - used to open-code the exception
+ *
+ * EXC_{REAL|VIRT}  - standard exception
+ *
+ * EXC_{REAL|VIRT}_suffix
+ *     where _suffix is:
+ *   - _MASKABLE               - maskable exception
+ *   - _OOL                    - out of line with trampoline to common handler
+ *   - _HV                     - HV exception
+ *
+ * There can be combinations, e.g., EXC_VIRT_OOL_MASKABLE_HV
+ *
+ * The one unusual case is __EXC_REAL_OOL_HV_DIRECT, which is
+ * an OOL vector that branches to a specified handler rather than the usual
+ * trampoline that goes to common. It, and other underscore macros, should
+ * be used with care.
+ *
+ * KVM handlers come in the following verieties:
+ * TRAMP_KVM
+ * TRAMP_KVM_SKIP
+ * TRAMP_KVM_HV
+ * TRAMP_KVM_HV_SKIP
+ *
+ * COMMON handlers come in the following verieties:
+ * EXC_COMMON_BEGIN/END - used to open-code the handler
+ * EXC_COMMON
+ * EXC_COMMON_ASYNC
+ * EXC_COMMON_HV
+ *
+ * TRAMP_REAL and TRAMP_VIRT can be used with BEGIN/END. KVM
+ * and OOL handlers are implemented as types of TRAMP and TRAMP_VIRT handlers.
+ */
+
 #define EXC_REAL_BEGIN(name, start, end)			\
-	. = start ;							\
-	.global exc_real_##start##_##name ;				\
-exc_real_##start##_##name:
+	FIXED_SECTION_ENTRY_BEGIN_LOCATION(real_vectors, exc_real_##start##_##name, start)
 
-#define EXC_REAL_END(name, start, end)
+#define EXC_REAL_END(name, start, end)			\
+	FIXED_SECTION_ENTRY_END_LOCATION(real_vectors, exc_real_##start##_##name, end)
 
 #define EXC_VIRT_BEGIN(name, start, end)			\
-	. = start ;							\
-	.global exc_virt_##start##_##name ;				\
-exc_virt_##start##_##name:
+	FIXED_SECTION_ENTRY_BEGIN_LOCATION(virt_vectors, exc_virt_##start##_##name, start)
 
-#define EXC_VIRT_END(name, start, end)
+#define EXC_VIRT_END(name, start, end)			\
+	FIXED_SECTION_ENTRY_END_LOCATION(virt_vectors, exc_virt_##start##_##name, end)
 
 #define EXC_COMMON_BEGIN(name)					\
+	USE_TEXT_SECTION();						\
 	.align	7;							\
 	.global name;							\
+	DEFINE_FIXED_SYMBOL(name);					\
 name:
 
 #define TRAMP_REAL_BEGIN(name)					\
-	.global name ;							\
-name:
+	FIXED_SECTION_ENTRY_BEGIN(real_trampolines, name)
+
+#define TRAMP_VIRT_BEGIN(name)					\
+	FIXED_SECTION_ENTRY_BEGIN(virt_trampolines, name)
 
 #ifdef CONFIG_KVM_BOOK3S_64_HANDLER
 #define TRAMP_KVM_BEGIN(name)						\
@@ -33,9 +223,13 @@ name:
 #define TRAMP_KVM_BEGIN(name)
 #endif
 
-#define EXC_REAL_NONE(start, end)
+#define EXC_REAL_NONE(start, end)				\
+	FIXED_SECTION_ENTRY_BEGIN_LOCATION(real_vectors, exc_real_##start##_##unused, start); \
+	FIXED_SECTION_ENTRY_END_LOCATION(real_vectors, exc_real_##start##_##unused, end)
 
-#define EXC_VIRT_NONE(start, end)
+#define EXC_VIRT_NONE(start, end)				\
+	FIXED_SECTION_ENTRY_BEGIN_LOCATION(virt_vectors, exc_virt_##start##_##unused, start); \
+	FIXED_SECTION_ENTRY_END_LOCATION(virt_vectors, exc_virt_##start##_##unused, end);
 
 
 #define EXC_REAL(name, start, end)				\
@@ -77,6 +271,10 @@ name:
 	TRAMP_REAL_BEGIN(tramp_real_##name);				\
 	STD_EXCEPTION_PSERIES_OOL(vec, name##_common);			\
 
+#define EXC_REAL_OOL(name, start, end)			\
+	__EXC_REAL_OOL(name, start, end);			\
+	__TRAMP_REAL_REAL_OOL(name, start);
+
 #define __EXC_REAL_OOL_MASKABLE(name, start, end)		\
 	__EXC_REAL_OOL(name, start, end);
 
@@ -84,6 +282,10 @@ name:
 	TRAMP_REAL_BEGIN(tramp_real_##name);				\
 	MASKABLE_EXCEPTION_PSERIES_OOL(vec, name##_common);		\
 
+#define EXC_REAL_OOL_MASKABLE(name, start, end)		\
+	__EXC_REAL_OOL_MASKABLE(name, start, end);		\
+	__TRAMP_REAL_REAL_OOL_MASKABLE(name, start);
+
 #define __EXC_REAL_OOL_HV_DIRECT(name, start, end, handler)	\
 	EXC_REAL_BEGIN(name, start, end);			\
 	__OOL_EXCEPTION(start, label, handler);				\
@@ -96,6 +298,10 @@ name:
 	TRAMP_REAL_BEGIN(tramp_real_##name);				\
 	STD_EXCEPTION_HV_OOL(vec, name##_common);			\
 
+#define EXC_REAL_OOL_HV(name, start, end)			\
+	__EXC_REAL_OOL_HV(name, start, end);			\
+	__TRAMP_REAL_REAL_OOL_HV(name, start);
+
 #define __EXC_REAL_OOL_MASKABLE_HV(name, start, end)		\
 	__EXC_REAL_OOL(name, start, end);
 
@@ -103,36 +309,56 @@ name:
 	TRAMP_REAL_BEGIN(tramp_real_##name);				\
 	MASKABLE_EXCEPTION_HV_OOL(vec, name##_common);			\
 
+#define EXC_REAL_OOL_MASKABLE_HV(name, start, end)		\
+	__EXC_REAL_OOL_MASKABLE_HV(name, start, end);	\
+	__TRAMP_REAL_REAL_OOL_MASKABLE_HV(name, start);
+
 #define __EXC_VIRT_OOL(name, start, end)			\
 	EXC_VIRT_BEGIN(name, start, end);			\
 	__OOL_EXCEPTION(start, label, tramp_virt_##name);		\
 	EXC_VIRT_END(name, start, end);
 
 #define __TRAMP_REAL_VIRT_OOL(name, realvec)				\
-	TRAMP_REAL_BEGIN(tramp_virt_##name);				\
+	TRAMP_VIRT_BEGIN(tramp_virt_##name);			\
 	STD_RELON_EXCEPTION_PSERIES_OOL(realvec, name##_common);	\
 
+#define EXC_VIRT_OOL(name, start, end, realvec)		\
+	__EXC_VIRT_OOL(name, start, end);			\
+	__TRAMP_REAL_VIRT_OOL(name, realvec);
+
 #define __EXC_VIRT_OOL_MASKABLE(name, start, end)		\
 	__EXC_VIRT_OOL(name, start, end);
 
 #define __TRAMP_REAL_VIRT_OOL_MASKABLE(name, realvec)		\
-	TRAMP_REAL_BEGIN(tramp_virt_##name);				\
+	TRAMP_VIRT_BEGIN(tramp_virt_##name);			\
 	MASKABLE_RELON_EXCEPTION_PSERIES_OOL(realvec, name##_common);	\
 
+#define EXC_VIRT_OOL_MASKABLE(name, start, end, realvec)	\
+	__EXC_VIRT_OOL_MASKABLE(name, start, end);		\
+	__TRAMP_REAL_VIRT_OOL_MASKABLE(name, realvec);
+
 #define __EXC_VIRT_OOL_HV(name, start, end)			\
 	__EXC_VIRT_OOL(name, start, end);
 
 #define __TRAMP_REAL_VIRT_OOL_HV(name, realvec)			\
-	TRAMP_REAL_BEGIN(tramp_virt_##name);				\
+	TRAMP_VIRT_BEGIN(tramp_virt_##name);			\
 	STD_RELON_EXCEPTION_HV_OOL(realvec, name##_common);		\
 
+#define EXC_VIRT_OOL_HV(name, start, end, realvec)		\
+	__EXC_VIRT_OOL_HV(name, start, end);			\
+	__TRAMP_REAL_VIRT_OOL_HV(name, realvec);
+
 #define __EXC_VIRT_OOL_MASKABLE_HV(name, start, end)		\
 	__EXC_VIRT_OOL(name, start, end);
 
 #define __TRAMP_REAL_VIRT_OOL_MASKABLE_HV(name, realvec)		\
-	TRAMP_REAL_BEGIN(tramp_virt_##name);				\
+	TRAMP_VIRT_BEGIN(tramp_virt_##name);			\
 	MASKABLE_RELON_EXCEPTION_HV_OOL(realvec, name##_common);	\
 
+#define EXC_VIRT_OOL_MASKABLE_HV(name, start, end, realvec)	\
+	__EXC_VIRT_OOL_MASKABLE_HV(name, start, end);	\
+	__TRAMP_REAL_VIRT_OOL_MASKABLE_HV(name, realvec);
+
 #define TRAMP_KVM(area, n)						\
 	TRAMP_KVM_BEGIN(do_kvm_##n);					\
 	KVM_HANDLER(area, EXC_STD, n);					\
@@ -141,6 +367,9 @@ name:
 	TRAMP_KVM_BEGIN(do_kvm_##n);					\
 	KVM_HANDLER_SKIP(area, EXC_STD, n);				\
 
+/*
+ * HV variant exceptions get the 0x2 bit added to their trap number.
+ */
 #define TRAMP_KVM_HV(area, n)						\
 	TRAMP_KVM_BEGIN(do_kvm_H##n);					\
 	KVM_HANDLER(area, EXC_HV, n + 0x2);				\