Author: jhb
Date: Wed Dec 14 00:18:12 2016
New Revision: 310045
URL: https://svnweb.freebsd.org/changeset/base/310045
Log:
Use casts to force an unsigned comparison in db_search_symbol().
On all of our platforms, db_expr_t is a signed integer while
db_addr_t is an unsigned integer value. db_search_symbol used variables
of type db_expr_t to hold the current offset of the requested address from
the "best" symbol found so far. This value was initialized to '~0'.
When a new symbol is found from a symbol table, the associated diff for the
new symbol is compared against the existing value as 'if (newdiff < diff)'
to determine if the new symbol had a smaller diff and was thus a closer
match.
On 64-bit MIPS, the '~0' was treated as a negative value (-1). A lookup
that found a perfect match of an address against a symbol returned a diff
of 0. However, in signed comparisons, 0 is not less than -1. As a result,
DDB on 64-bit MIPS never resolved any addresses to symbols. Workaround
this by using casts to force an unsigned comparison.
Probably the diff returned from db_search_symbol() and X_db_search_symbol()
should be changed to a db_addr_t instead of a db_expr_t as it is an
unsigned value (and is an offset of an address, so should fit in the same
size as an address).
Sponsored by: DARPA / AFRL
Modified:
head/sys/ddb/db_sym.c
Modified: head/sys/ddb/db_sym.c
==============================================================================
--- head/sys/ddb/db_sym.c Tue Dec 13 23:34:07 2016 (r310044)
+++ head/sys/ddb/db_sym.c Wed Dec 14 00:18:12 2016 (r310045)
@@ -373,10 +373,10 @@ db_search_symbol(db_addr_t val, db_strat
register int i;
c_db_sym_t ret = C_DB_SYM_NULL, sym;
- newdiff = diff = ~0;
+ newdiff = diff = val;
for (i = 0; i < db_nsymtab; i++) {
sym = X_db_search_symbol(&db_symtabs[i], val, strategy, &newdiff);
- if (newdiff < diff) {
+ if ((uintmax_t)newdiff < (uintmax_t)diff) {
db_last_symtab = &db_symtabs[i];
diff = newdiff;
ret = sym;
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