[PATCH] symbols: don't over-align data

[Jan Beulich <jbeulich@xxxxxxxx>]

Arrays of .byte or .short don't really need aligning better than 1 or 2
bytes respectively. Arrays of .long also don't need aligning to 8 bytes
(which would have happened when BITS_PER_LONG is 64 and SYMBOLS_ORIGIN is
not defined).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Strictly speaking, however, we may have been under-aligning the arrays for
x86-64: The psABI mandates
"An array uses the same alignment as its elements, except that a local or
 global array variable of length at least 16 bytes or a C99 variable-
 length array variable always has alignment of at least 16 bytes."
I don't think the compiler can leverage that though, as long as we declare
the arrays as incomplete ones (without dimension). Note the subtlety
though: C99 distinguishes [] and [*] (only the latter being "variable
length"), while the psABI may not mean to limit its constraint to the
latter form.

This, contextually (not functionally), goes on top of "symbols: check
table sizes don't change between linking passes 2 and 3"

--- a/xen/tools/symbols.c
+++ b/xen/tools/symbols.c
@@ -252,7 +252,7 @@ static void read_map(FILE *in)
        }
 }
 
-static void output_label(const char *label, bool keep)
+static void output_label(const char *label, const char *align, bool keep)
 {
        static bool pending;
 
@@ -266,10 +266,10 @@ static void output_label(const char *lab
                return;
 
        if (symbol_prefix_char) {
-               printf("DATA(%c%s, ALGN)\n", symbol_prefix_char, label);
+               printf("DATA(%c%s, %s)\n", symbol_prefix_char, label, align);
                printf("#define CURRENT %c%s\n", symbol_prefix_char, label);
        } else {
-               printf("DATA(%s, ALGN)\n", label);
+               printf("DATA(%s, %s)\n", label, align);
                printf("#define CURRENT %s\n", label);
        }
 }
@@ -353,9 +353,9 @@ static void write_src(void)
 
        printf("#ifndef SYMBOLS_ORIGIN\n");
        printf("#define SYMBOLS_ORIGIN 0\n");
-       output_label("symbols_addresses", false);
+       output_label("symbols_addresses", "ALGN", false);
        printf("#else\n");
-       output_label("symbols_offsets", true);
+       output_label("symbols_offsets", "ALGN", true);
        printf("#endif\n");
        for (i = 0, ends = 0; i < table_cnt; i++) {
                printf("\tPTR\t%#llx - SYMBOLS_ORIGIN\n", table[i].addr);
@@ -380,14 +380,14 @@ static void write_src(void)
                       table[i].addr + table[i].size);
        }
 
-       output_label("symbols_num_addrs", false);
+       output_label("symbols_num_addrs", "4", false);
        printf("\t.long\t%d\n", table_cnt + ends);
 
        /* table of offset markers, that give the offset in the compressed 
stream
         * every 256 symbols */
        markers = malloc(sizeof(*markers) * ((table_cnt + ends + 255) >> 8));
 
-       output_label("symbols_names", false);
+       output_label("symbols_names", "1", false);
        for (i = 0, off = 0, ends = 0; i < table_cnt; i++) {
                if (((i + ends) & 0xFF) == 0)
                        markers[(i + ends) >> 8] = off;
@@ -412,11 +412,11 @@ static void write_src(void)
                ++off;
        }
 
-       output_label("symbols_markers", false);
+       output_label("symbols_markers", "4", false);
        for (i = 0; i < ((table_cnt + ends + 255) >> 8); i++)
                printf("\t.long\t%d\n", markers[i]);
 
-       output_label("symbols_token_table", false);
+       output_label("symbols_token_table", "1", false);
        off = 0;
        for (i = 0; i < 256; i++) {
                best_idx[i] = off;
@@ -425,12 +425,12 @@ static void write_src(void)
                off += strlen(buf) + 1;
        }
 
-       output_label("symbols_token_index", false);
+       output_label("symbols_token_index", "2", false);
        for (i = 0; i < 256; i++)
                printf("\t.short\t%d\n", best_idx[i]);
 
        if (sort_by_name) {
-               output_label("symbols_num_names", false);
+               output_label("symbols_num_names", "4", false);
                printf("\t.long\t%d\n", table_cnt);
 
                /* Sorted by original symbol names and type. */
@@ -439,12 +439,12 @@ static void write_src(void)
                /* A fixed sized array with two entries: offset in the
                 * compressed stream (for symbol name), and offset in
                 * symbols_addresses (or symbols_offset). */
-               output_label("symbols_sorted_offsets", false);
+               output_label("symbols_sorted_offsets", "4", false);
                for (i = 0; i < table_cnt; i++)
                        printf("\t.long %u, %u\n", table[i].stream_offset, 
table[i].addr_idx);
        }
 
-       output_label(NULL, false);
+       output_label(NULL, NULL, false);
        free(markers);
 }