[PATCH] x86-64: Speed up dwarf2 unwinder

This changes the dwarf2 unwinder to do a binary search for CIEs
instead of a linear work. The linker is unfortunately not
able to build a proper lookup table at link time, instead it creates
one at runtime as soon as the bootmem allocator is usable (so you'll continue
using the linear lookup for the first [hopefully] few calls).
The code should be ready to utilize a build-time created table once
a fixed linker becomes available.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>

diff --git a/Makefile b/Makefile
index 62a1343..389ff0c 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -499,6 +499,7 @@ endif
 
 ifdef CONFIG_UNWIND_INFO
 CFLAGS         += -fasynchronous-unwind-tables
+LDFLAGS_vmlinux        += --eh-frame-hdr
 endif
 
 ifdef CONFIG_DEBUG_INFO

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 69240b5..9d0d11c 100644 (file)
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -125,6 +125,10 @@
                *(__param)                                              \
                VMLINUX_SYMBOL(__stop___param) = .;                     \
        }                                                               \
+                                                                       \
+       /* Unwind data binary search table */                           \
+       EH_FRAME_HDR                                                    \
+                                                                       \
        __end_rodata = .;                                               \
        . = ALIGN(4096);
 
@@ -157,6 +161,18 @@
                *(.kprobes.text)                                        \
                VMLINUX_SYMBOL(__kprobes_text_end) = .;
 
+#ifdef CONFIG_STACK_UNWIND
+               /* Unwind data binary search table */
+#define EH_FRAME_HDR                                                   \
+               .eh_frame_hdr : AT(ADDR(.eh_frame_hdr) - LOAD_OFFSET) { \
+                       VMLINUX_SYMBOL(__start_unwind_hdr) = .;         \
+                       *(.eh_frame_hdr)                                \
+                       VMLINUX_SYMBOL(__end_unwind_hdr) = .;           \
+               }
+#else
+#define EH_FRAME_HDR
+#endif
+
                /* DWARF debug sections.
                Symbols in the DWARF debugging sections are relative to
                the beginning of the section so we begin them at 0.  */

diff --git a/include/linux/unwind.h b/include/linux/unwind.h
index 73e1751..749928c 100644 (file)
--- a/include/linux/unwind.h
+++ b/include/linux/unwind.h
@@ -26,6 +26,7 @@ struct module;
  * Initialize unwind support.
  */
 extern void unwind_init(void);
+extern void unwind_setup(void);
 
 #ifdef CONFIG_MODULES
 
@@ -73,6 +74,7 @@ extern int unwind_to_user(struct unwind_frame_info *);
 struct unwind_frame_info {};
 
 static inline void unwind_init(void) {}
+static inline void unwind_setup(void) {}
 
 #ifdef CONFIG_MODULES
 

diff --git a/init/main.c b/init/main.c
index ee12324..36f608a 100644 (file)
--- a/init/main.c
+++ b/init/main.c
@@ -503,6 +503,7 @@ asmlinkage void __init start_kernel(void)
        printk(KERN_NOTICE);
        printk(linux_banner);
        setup_arch(&command_line);
+       unwind_setup();
        setup_per_cpu_areas();
        smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
 

diff --git a/kernel/unwind.c b/kernel/unwind.c
index 2e23686..f7e50d1 100644 (file)
--- a/kernel/unwind.c
+++ b/kernel/unwind.c
@@ -11,13 +11,15 @@
 
 #include <linux/unwind.h>
 #include <linux/module.h>
-#include <linux/delay.h>
+#include <linux/bootmem.h>
+#include <linux/sort.h>
 #include <linux/stop_machine.h>
 #include <asm/sections.h>
 #include <asm/uaccess.h>
 #include <asm/unaligned.h>
 
 extern char __start_unwind[], __end_unwind[];
+extern const u8 __start_unwind_hdr[], __end_unwind_hdr[];
 
 #define MAX_STACK_DEPTH 8
 
@@ -100,6 +102,8 @@ static struct unwind_table {
        } core, init;
        const void *address;
        unsigned long size;
+       const unsigned char *header;
+       unsigned long hdrsz;
        struct unwind_table *link;
        const char *name;
 } root_table;
@@ -145,6 +149,10 @@ static struct unwind_table *find_table(unsigned long pc)
        return table;
 }
 
+static unsigned long read_pointer(const u8 **pLoc,
+                                  const void *end,
+                                  signed ptrType);
+
 static void init_unwind_table(struct unwind_table *table,
                               const char *name,
                               const void *core_start,
@@ -152,14 +160,30 @@ static void init_unwind_table(struct unwind_table *table,
                               const void *init_start,
                               unsigned long init_size,
                               const void *table_start,
-                              unsigned long table_size)
+                              unsigned long table_size,
+                              const u8 *header_start,
+                              unsigned long header_size)
 {
+       const u8 *ptr = header_start + 4;
+       const u8 *end = header_start + header_size;
+
        table->core.pc = (unsigned long)core_start;
        table->core.range = core_size;
        table->init.pc = (unsigned long)init_start;
        table->init.range = init_size;
        table->address = table_start;
        table->size = table_size;
+       /* See if the linker provided table looks valid. */
+       if (header_size <= 4
+           || header_start[0] != 1
+           || (void *)read_pointer(&ptr, end, header_start[1]) != table_start
+           || header_start[2] == DW_EH_PE_omit
+           || read_pointer(&ptr, end, header_start[2]) <= 0
+           || header_start[3] == DW_EH_PE_omit)
+               header_start = NULL;
+       table->hdrsz = header_size;
+       smp_wmb();
+       table->header = header_start;
        table->link = NULL;
        table->name = name;
 }
@@ -169,7 +193,143 @@ void __init unwind_init(void)
        init_unwind_table(&root_table, "kernel",
                          _text, _end - _text,
                          NULL, 0,
-                         __start_unwind, __end_unwind - __start_unwind);
+                         __start_unwind, __end_unwind - __start_unwind,
+                         __start_unwind_hdr, __end_unwind_hdr - __start_unwind_hdr);
+}
+
+static const u32 bad_cie, not_fde;
+static const u32 *cie_for_fde(const u32 *fde, const struct unwind_table *);
+static signed fde_pointer_type(const u32 *cie);
+
+struct eh_frame_hdr_table_entry {
+       unsigned long start, fde;
+};
+
+static int cmp_eh_frame_hdr_table_entries(const void *p1, const void *p2)
+{
+       const struct eh_frame_hdr_table_entry *e1 = p1;
+       const struct eh_frame_hdr_table_entry *e2 = p2;
+
+       return (e1->start > e2->start) - (e1->start < e2->start);
+}
+
+static void swap_eh_frame_hdr_table_entries(void *p1, void *p2, int size)
+{
+       struct eh_frame_hdr_table_entry *e1 = p1;
+       struct eh_frame_hdr_table_entry *e2 = p2;
+       unsigned long v;
+
+       v = e1->start;
+       e1->start = e2->start;
+       e2->start = v;
+       v = e1->fde;
+       e1->fde = e2->fde;
+       e2->fde = v;
+}
+
+static void __init setup_unwind_table(struct unwind_table *table,
+                                       void *(*alloc)(unsigned long))
+{
+       const u8 *ptr;
+       unsigned long tableSize = table->size, hdrSize;
+       unsigned n;
+       const u32 *fde;
+       struct {
+               u8 version;
+               u8 eh_frame_ptr_enc;
+               u8 fde_count_enc;
+               u8 table_enc;
+               unsigned long eh_frame_ptr;
+               unsigned int fde_count;
+               struct eh_frame_hdr_table_entry table[];
+       } __attribute__((__packed__)) *header;
+
+       if (table->header)
+               return;
+
+       if (table->hdrsz)
+               printk(KERN_WARNING ".eh_frame_hdr for '%s' present but unusable\n",
+                      table->name);
+
+       if (tableSize & (sizeof(*fde) - 1))
+               return;
+
+       for (fde = table->address, n = 0;
+            tableSize > sizeof(*fde) && tableSize - sizeof(*fde) >= *fde;
+            tableSize -= sizeof(*fde) + *fde, fde += 1 + *fde / sizeof(*fde)) {
+               const u32 *cie = cie_for_fde(fde, table);
+               signed ptrType;
+
+               if (cie == &not_fde)
+                       continue;
+               if (cie == NULL
+                   || cie == &bad_cie
+                   || (ptrType = fde_pointer_type(cie)) < 0)
+                       return;
+               ptr = (const u8 *)(fde + 2);
+               if (!read_pointer(&ptr,
+                                 (const u8 *)(fde + 1) + *fde,
+                                 ptrType))
+                       return;
+               ++n;
+       }
+
+       if (tableSize || !n)
+               return;
+
+       hdrSize = 4 + sizeof(unsigned long) + sizeof(unsigned int)
+               + 2 * n * sizeof(unsigned long);
+       header = alloc(hdrSize);
+       if (!header)
+               return;
+       header->version          = 1;
+       header->eh_frame_ptr_enc = DW_EH_PE_abs|DW_EH_PE_native;
+       header->fde_count_enc    = DW_EH_PE_abs|DW_EH_PE_data4;
+       header->table_enc        = DW_EH_PE_abs|DW_EH_PE_native;
+       put_unaligned((unsigned long)table->address, &header->eh_frame_ptr);
+       BUILD_BUG_ON(offsetof(typeof(*header), fde_count)
+                    % __alignof(typeof(header->fde_count)));
+       header->fde_count        = n;
+
+       BUILD_BUG_ON(offsetof(typeof(*header), table)
+                    % __alignof(typeof(*header->table)));
+       for (fde = table->address, tableSize = table->size, n = 0;
+            tableSize;
+            tableSize -= sizeof(*fde) + *fde, fde += 1 + *fde / sizeof(*fde)) {
+               const u32 *cie = fde + 1 - fde[1] / sizeof(*fde);
+
+               if (!fde[1])
+                       continue; /* this is a CIE */
+               ptr = (const u8 *)(fde + 2);
+               header->table[n].start = read_pointer(&ptr,
+                                                     (const u8 *)(fde + 1) + *fde,
+                                                     fde_pointer_type(cie));
+               header->table[n].fde = (unsigned long)fde;
+               ++n;
+       }
+       WARN_ON(n != header->fde_count);
+
+       sort(header->table,
+            n,
+            sizeof(*header->table),
+            cmp_eh_frame_hdr_table_entries,
+            swap_eh_frame_hdr_table_entries);
+
+       table->hdrsz = hdrSize;
+       smp_wmb();
+       table->header = (const void *)header;
+}
+
+static void *__init balloc(unsigned long sz)
+{
+       return __alloc_bootmem_nopanic(sz,
+                                      sizeof(unsigned int),
+                                      __pa(MAX_DMA_ADDRESS));
+}
+
+void __init unwind_setup(void)
+{
+       setup_unwind_table(&root_table, balloc);
 }
 
 #ifdef CONFIG_MODULES
@@ -193,7 +353,8 @@ void *unwind_add_table(struct module *module,
        init_unwind_table(table, module->name,
                          module->module_core, module->core_size,
                          module->module_init, module->init_size,
-                         table_start, table_size);
+                         table_start, table_size,
+                         NULL, 0);
 
        if (last_table)
                last_table->link = table;
@@ -303,6 +464,26 @@ static sleb128_t get_sleb128(const u8 **pcur, const u8 *end)
        return value;
 }
 
+static const u32 *cie_for_fde(const u32 *fde, const struct unwind_table *table)
+{
+       const u32 *cie;
+
+       if (!*fde || (*fde & (sizeof(*fde) - 1)))
+               return &bad_cie;
+       if (!fde[1])
+               return &not_fde; /* this is a CIE */
+       if ((fde[1] & (sizeof(*fde) - 1))
+           || fde[1] > (unsigned long)(fde + 1) - (unsigned long)table->address)
+               return NULL; /* this is not a valid FDE */
+       cie = fde + 1 - fde[1] / sizeof(*fde);
+       if (*cie <= sizeof(*cie) + 4
+           || *cie >= fde[1] - sizeof(*fde)
+           || (*cie & (sizeof(*cie) - 1))
+           || cie[1])
+               return NULL; /* this is not a (valid) CIE */
+       return cie;
+}
+
 static unsigned long read_pointer(const u8 **pLoc,
                                   const void *end,
                                   signed ptrType)
@@ -610,49 +791,108 @@ int unwind(struct unwind_frame_info *frame)
        unsigned i;
        signed ptrType = -1;
        uleb128_t retAddrReg = 0;
-       struct unwind_table *table;
+       const struct unwind_table *table;
        struct unwind_state state;
 
        if (UNW_PC(frame) == 0)
                return -EINVAL;
        if ((table = find_table(pc)) != NULL
            && !(table->size & (sizeof(*fde) - 1))) {
-               unsigned long tableSize = table->size;
-
-               for (fde = table->address;
-                    tableSize > sizeof(*fde) && tableSize - sizeof(*fde) >= *fde;
-                    tableSize -= sizeof(*fde) + *fde,
-                    fde += 1 + *fde / sizeof(*fde)) {
-                       if (!*fde || (*fde & (sizeof(*fde) - 1)))
-                               break;
-                       if (!fde[1])
-                               continue; /* this is a CIE */
-                       if ((fde[1] & (sizeof(*fde) - 1))
-                           || fde[1] > (unsigned long)(fde + 1)
-                                       - (unsigned long)table->address)
-                               continue; /* this is not a valid FDE */
-                       cie = fde + 1 - fde[1] / sizeof(*fde);
-                       if (*cie <= sizeof(*cie) + 4
-                           || *cie >= fde[1] - sizeof(*fde)
-                           || (*cie & (sizeof(*cie) - 1))
-                           || cie[1]
-                           || (ptrType = fde_pointer_type(cie)) < 0) {
-                               cie = NULL; /* this is not a (valid) CIE */
-                               continue;
+               const u8 *hdr = table->header;
+               unsigned long tableSize;
+
+               smp_rmb();
+               if (hdr && hdr[0] == 1) {
+                       switch(hdr[3] & DW_EH_PE_FORM) {
+                       case DW_EH_PE_native: tableSize = sizeof(unsigned long); break;
+                       case DW_EH_PE_data2: tableSize = 2; break;
+                       case DW_EH_PE_data4: tableSize = 4; break;
+                       case DW_EH_PE_data8: tableSize = 8; break;
+                       default: tableSize = 0; break;
+                       }
+                       ptr = hdr + 4;
+                       end = hdr + table->hdrsz;
+                       if (tableSize
+                           && read_pointer(&ptr, end, hdr[1])
+                              == (unsigned long)table->address
+                           && (i = read_pointer(&ptr, end, hdr[2])) > 0
+                           && i == (end - ptr) / (2 * tableSize)
+                           && !((end - ptr) % (2 * tableSize))) {
+                               do {
+                                       const u8 *cur = ptr + (i / 2) * (2 * tableSize);
+
+                                       startLoc = read_pointer(&cur,
+                                                               cur + tableSize,
+                                                               hdr[3]);
+                                       if (pc < startLoc)
+                                               i /= 2;
+                                       else {
+                                               ptr = cur - tableSize;
+                                               i = (i + 1) / 2;
+                                       }
+                               } while (startLoc && i > 1);
+                               if (i == 1
+                                   && (startLoc = read_pointer(&ptr,
+                                                               ptr + tableSize,
+                                                               hdr[3])) != 0
+                                   && pc >= startLoc)
+                                       fde = (void *)read_pointer(&ptr,
+                                                                  ptr + tableSize,
+                                                                  hdr[3]);
                        }
+               }
+
+               if (fde != NULL) {
+                       cie = cie_for_fde(fde, table);
                        ptr = (const u8 *)(fde + 2);
-                       startLoc = read_pointer(&ptr,
-                                               (const u8 *)(fde + 1) + *fde,
-                                               ptrType);
-                       endLoc = startLoc
-                                + read_pointer(&ptr,
-                                               (const u8 *)(fde + 1) + *fde,
-                                               ptrType & DW_EH_PE_indirect
-                                               ? ptrType
-                                               : ptrType & (DW_EH_PE_FORM|DW_EH_PE_signed));
-                       if (pc >= startLoc && pc < endLoc)
-                               break;
-                       cie = NULL;
+                       if(cie != NULL
+                          && cie != &bad_cie
+                          && cie != &not_fde
+                          && (ptrType = fde_pointer_type(cie)) >= 0
+                          && read_pointer(&ptr,
+                                          (const u8 *)(fde + 1) + *fde,
+                                          ptrType) == startLoc) {
+                               if (!(ptrType & DW_EH_PE_indirect))
+                                       ptrType &= DW_EH_PE_FORM|DW_EH_PE_signed;
+                               endLoc = startLoc
+                                        + read_pointer(&ptr,
+                                                       (const u8 *)(fde + 1) + *fde,
+                                                       ptrType);
+                               if(pc >= endLoc)
+                                       fde = NULL;
+                       } else
+                               fde = NULL;
+               }
+               if (fde == NULL) {
+                       for (fde = table->address, tableSize = table->size;
+                            cie = NULL, tableSize > sizeof(*fde)
+                            && tableSize - sizeof(*fde) >= *fde;
+                            tableSize -= sizeof(*fde) + *fde,
+                            fde += 1 + *fde / sizeof(*fde)) {
+                               cie = cie_for_fde(fde, table);
+                               if (cie == &bad_cie) {
+                                       cie = NULL;
+                                       break;
+                               }
+                               if (cie == NULL
+                                   || cie == &not_fde
+                                   || (ptrType = fde_pointer_type(cie)) < 0)
+                                       continue;
+                               ptr = (const u8 *)(fde + 2);
+                               startLoc = read_pointer(&ptr,
+                                                       (const u8 *)(fde + 1) + *fde,
+                                                       ptrType);
+                               if (!startLoc)
+                                       continue;
+                               if (!(ptrType & DW_EH_PE_indirect))
+                                       ptrType &= DW_EH_PE_FORM|DW_EH_PE_signed;
+                               endLoc = startLoc
+                                        + read_pointer(&ptr,
+                                                       (const u8 *)(fde + 1) + *fde,
+                                                       ptrType);
+                               if (pc >= startLoc && pc < endLoc)
+                                       break;
+                       }
                }
        }
        if (cie != NULL) {