On 2025-04-02 09:58, Jan Beulich wrote:
When determining the symbol for a given address (e.g. for the %pS
logging format specifier), so far the size of a symbol (function) was
assumed to be everything until the next symbol. There may be gaps
though, which would better be recognizable in output (often suggesting
something odd is going on).
Insert "fake" end symbols in the address table, accompanied by zero-
length type/name entries (to keep lookup reasonably close to how it
was).
Note however that this, with present GNU binutils, won't work for
xen.efi: The linker loses function sizes (they're not part of a normal
symbol table entry), and hence nm has no way of reporting them.
The address table growth is quite significant on x86 release builds (due
to functions being aligned to 16-byte boundaries), though: Its size
almost doubles.
Requested-by: Andrew Cooper <andrew.coop...@citrix.com>
Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
Note: Style-wise this is a horrible mix. I'm trying to match styles with
what's used in the respective functions.
Older GNU ld retains section symbols, which nm then also lists. Should
we perhaps strip those as we read in nm's output? They don't provide any
useful extra information, as our linker scripts add section start
symbols anyway. (For the purposes here, luckily such section symbols are
at least emitted without size.)
Even for section start symbols there is the question of whether they
really need retaining (except perhaps when producing a map file). The
main question here likely is whether livepatch may have a need to look
them up by name. (Section end symbols may actually be slightly more
useful to keep, but that may also want considering more closely.)
---
--- a/xen/tools/symbols.c
+++ b/xen/tools/symbols.c
@@ -318,24 +334,42 @@ static void write_src(void)
printf("#else\n");
output_label("symbols_offsets");
printf("#endif\n");
- for (i = 0; i < table_cnt; i++) {
+ for (i = 0, ends = 0; i < table_cnt; i++) {
printf("\tPTR\t%#llx - SYMBOLS_ORIGIN\n", table[i].addr);
+
+ table[i].addr_idx = i + ends;
+
+ if (!want_symbol_end(i)) {
+ /* If there's another symbol at the same address,
+ * propagate this symbol's size if the next one has
+ * no size, or if the next one's size is larger. */
Why do we want to shrink the next symbol's size?
The code looks good - I just don't understand this condition.
Thanks,
Jason
+ if (table[i].size &&
+ i + 1 < table_cnt &&
+ table[i + 1].addr == table[i].addr &&
+ (!table[i + 1].size ||
+ table[i + 1].size > table[i].size))
+ table[i + 1].size = table[i].size;
+ continue;
+ }
+
+ ++ends;
+ printf("\tPTR\t%#llx - SYMBOLS_ORIGIN\n",
+ table[i].addr + table[i].size);
}
printf("\n");
output_label("symbols_num_addrs");
- printf("\t.long\t%d\n", table_cnt);
+ printf("\t.long\t%d\n", table_cnt + ends);
printf("\n");
/* table of offset markers, that give the offset in the compressed stream
* every 256 symbols */
- markers = (unsigned int *) malloc(sizeof(unsigned int) * ((table_cnt +
255) / 256));
+ markers = malloc(sizeof(*markers) * ((table_cnt + ends + 255) >> 8));
output_label("symbols_names");
- off = 0;
- for (i = 0; i < table_cnt; i++) {
- if ((i & 0xFF) == 0)
- markers[i >> 8] = off;
+ for (i = 0, off = 0, ends = 0; i < table_cnt; i++) {
+ if (((i + ends) & 0xFF) == 0)
+ markers[(i + ends) >> 8] = off;
printf("\t.byte 0x%02x", table[i].len);
for (k = 0; k < table[i].len; k++)
