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xen-ia64-devel

[Xen-devel] [PATCH] x86-64: reduce symbol table size

To: <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] [PATCH] x86-64: reduce symbol table size
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Fri, 10 Jul 2009 15:26:30 +0100
Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Fri, 10 Jul 2009 07:27:05 -0700
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With all of Xen's symbols sitting within a 2Gb range on x86-64, they
can be referred to by the kallsyms-like offset table using 4- instead
of 8-byte slots.

The marker table can use 4-byte slots in all cases, just like the table
entry counts can (though that's only a minor improvement).

If ia64's PERCPU_ADDR got moved down to (KERNEL_START + 2Gb -
PERCPU_PAGE_SIZE), it could also utilize the more compact form.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- 2009-06-10.orig/xen/common/symbols.c        2007-04-02 12:16:26.000000000 
+0200
+++ 2009-06-10/xen/common/symbols.c     2009-06-30 16:58:32.000000000 +0200
@@ -18,21 +18,27 @@
 #include <xen/string.h>
 #include <xen/spinlock.h>
 
-extern unsigned long symbols_addresses[];
-extern unsigned long symbols_num_syms;
-extern u8 symbols_names[];
+#ifdef SYMBOLS_ORIGIN
+extern const unsigned int symbols_offsets[1];
+#define symbols_address(n) (SYMBOLS_ORIGIN + symbols_offsets[n])
+#else
+extern const unsigned long symbols_addresses[];
+#define symbols_address(n) symbols_addresses[n]
+#endif
+extern const unsigned int symbols_num_syms;
+extern const u8 symbols_names[];
 
-extern u8 symbols_token_table[];
-extern u16 symbols_token_index[];
+extern const u8 symbols_token_table[];
+extern const u16 symbols_token_index[];
 
-extern unsigned long symbols_markers[];
+extern const unsigned int symbols_markers[];
 
 /* expand a compressed symbol data into the resulting uncompressed string,
    given the offset to where the symbol is in the compressed stream */
 static unsigned int symbols_expand_symbol(unsigned int off, char *result)
 {
     int len, skipped_first = 0;
-    u8 *tptr, *data;
+    const u8 *tptr, *data;
 
     /* get the compressed symbol length from the first symbol byte */
     data = &symbols_names[off];
@@ -70,7 +76,7 @@ static unsigned int symbols_expand_symbo
  * symbols array */
 static unsigned int get_symbol_offset(unsigned long pos)
 {
-    u8 *name;
+    const u8 *name;
     int i;
 
     /* use the closest marker we have. We have markers every 256 positions,
@@ -107,13 +113,13 @@ const char *symbols_lookup(unsigned long
 
     while (high-low > 1) {
         mid = (low + high) / 2;
-        if (symbols_addresses[mid] <= addr) low = mid;
+        if (symbols_address(mid) <= addr) low = mid;
         else high = mid;
     }
 
     /* search for the first aliased symbol. Aliased symbols are
            symbols with the same address */
-    while (low && symbols_addresses[low - 1] == symbols_addresses[low])
+    while (low && symbols_address(low - 1) == symbols_address(low))
         --low;
 
         /* Grab name */
@@ -121,8 +127,8 @@ const char *symbols_lookup(unsigned long
 
     /* Search for next non-aliased symbol */
     for (i = low + 1; i < symbols_num_syms; i++) {
-        if (symbols_addresses[i] > symbols_addresses[low]) {
-            symbol_end = symbols_addresses[i];
+        if (symbols_address(i) > symbols_address(low)) {
+            symbol_end = symbols_address(i);
             break;
         }
     }
@@ -132,8 +138,8 @@ const char *symbols_lookup(unsigned long
         symbol_end = is_kernel_inittext(addr) ?
             (unsigned long)_einittext : (unsigned long)_etext;
 
-    *symbolsize = symbol_end - symbols_addresses[low];
-    *offset = addr - symbols_addresses[low];
+    *symbolsize = symbol_end - symbols_address(low);
+    *offset = addr - symbols_address(low);
     return namebuf;
 }
 
--- 2009-06-10.orig/xen/common/symbols-dummy.c  2006-10-04 08:49:30.000000000 
+0200
+++ 2009-06-10/xen/common/symbols-dummy.c       2009-06-30 16:55:43.000000000 
+0200
@@ -6,11 +6,15 @@
 #include <xen/config.h>
 #include <xen/types.h>
 
-unsigned long symbols_addresses[1];
-unsigned long symbols_num_syms;
-u8 symbols_names[1];
+#ifdef SYMBOLS_ORIGIN
+const unsigned int symbols_offsets[1];
+#else
+const unsigned long symbols_addresses[1];
+#endif
+const unsigned int symbols_num_syms;
+const u8 symbols_names[1];
 
-u8 symbols_token_table[1];
-u16 symbols_token_index[1];
+const u8 symbols_token_table[1];
+const u16 symbols_token_index[1];
 
-unsigned long symbols_markers[1];
+const unsigned int symbols_markers[1];
--- 2009-06-10.orig/xen/include/asm-x86/config.h        2009-06-10 
15:09:22.000000000 +0200
+++ 2009-06-10/xen/include/asm-x86/config.h     2009-06-30 16:52:22.000000000 
+0200
@@ -259,6 +259,8 @@ extern unsigned int video_mode, video_fl
 #define __HYPERVISOR_DS32 0xe010
 #define __HYPERVISOR_DS   __HYPERVISOR_DS64
 
+#define SYMBOLS_ORIGIN XEN_VIRT_START
+
 /* For generic assembly code: use macros to define operation/operand sizes. */
 #define __OS          "q"  /* Operation Suffix */
 #define __OP          "r"  /* Operand Prefix */
--- 2009-06-10.orig/xen/tools/symbols.c 2008-12-03 10:55:25.000000000 +0100
+++ 2009-06-10/xen/tools/symbols.c      2009-07-01 09:53:36.000000000 +0200
@@ -108,10 +108,7 @@ static int read_symbol(FILE *in, struct 
        else if (toupper((uint8_t)stype) == 'A')
        {
                /* Keep these useful absolute symbols */
-               if (strcmp(sym, "__kernel_syscall_via_break") &&
-                   strcmp(sym, "__kernel_syscall_via_epc") &&
-                   strcmp(sym, "__kernel_sigtramp") &&
-                   strcmp(sym, "__gp"))
+               if (strcmp(sym, "__gp"))
                        return -1;
 
        }
@@ -135,18 +132,9 @@ static int read_symbol(FILE *in, struct 
 static int symbol_valid(struct sym_entry *s)
 {
        /* Symbols which vary between passes.  Passes 1 and 2 must have
-        * identical symbol lists.  The symbols_* symbols below are only added
-        * after pass 1, they would be included in pass 2 when --all-symbols is
-        * specified so exclude them to get a stable symbol list.
+        * identical symbol lists.
         */
        static char *special_symbols[] = {
-               "symbols_addresses",
-               "symbols_num_syms",
-               "symbols_names",
-               "symbols_markers",
-               "symbols_token_table",
-               "symbols_token_index",
-
        /* Exclude linker generated symbols which vary between passes */
                "_SDA_BASE_",           /* ppc */
                "_SDA2_BASE_",          /* ppc */
@@ -251,8 +239,9 @@ static void write_src(void)
        unsigned int *markers;
        char buf[KSYM_NAME_LEN+1];
 
+       printf("#include <xen/config.h>\n");
        printf("#include <asm/types.h>\n");
-       printf("#if BITS_PER_LONG == 64\n");
+       printf("#if BITS_PER_LONG == 64 && !defined(SYMBOLS_ORIGIN)\n");
        printf("#define PTR .quad\n");
        printf("#define ALGN .align 8\n");
        printf("#else\n");
@@ -260,16 +249,21 @@ static void write_src(void)
        printf("#define ALGN .align 4\n");
        printf("#endif\n");
 
-       printf(".data\n");
+       printf("\t.section .rodata, \"a\"\n");
 
+       printf("#ifndef SYMBOLS_ORIGIN\n");
+       printf("#define SYMBOLS_ORIGIN 0\n");
        output_label("symbols_addresses");
+       printf("#else\n");
+       output_label("symbols_offsets");
+       printf("#endif\n");
        for (i = 0; i < table_cnt; i++) {
-               printf("\tPTR\t%#llx\n", table[i].addr);
+               printf("\tPTR\t%#llx - SYMBOLS_ORIGIN\n", table[i].addr);
        }
        printf("\n");
 
        output_label("symbols_num_syms");
-       printf("\tPTR\t%d\n", table_cnt);
+       printf("\t.long\t%d\n", table_cnt);
        printf("\n");
 
        /* table of offset markers, that give the offset in the compressed 
stream
@@ -293,7 +287,7 @@ static void write_src(void)
 
        output_label("symbols_markers");
        for (i = 0; i < ((table_cnt + 255) >> 8); i++)
-               printf("\tPTR\t%d\n", markers[i]);
+               printf("\t.long\t%d\n", markers[i]);
        printf("\n");
 
        free(markers);



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