On Thu, 24 Mar 2005, Bruce Evans wrote:
On Wed, 23 Mar 2005, Vinod Kashyap wrote:
...If any kernel module has the following, or a similar line in it: ----- char x[100] = {0}; ----- building of the GENERIC kernel on FreeBSD 5 -STABLE for amd64 as of 03/19/05, fails with the following message at the time of linking: "undefined reference to `memset'". ...Anyone knows what's happening?
gcc is expecting that memset() is in the library, but the FreeBSD kernel is freestanding and happens not to have memset() in its library.
As to why gcc calls memset() on amd64's but not on i386's: - gcc-3.3.3 doesn't call memset() on amd64's either. - gcc-3.4.2 on amd64's calls memset() starting with an array size of 65. It uses mov[qlwb] for sizes up to 16, then stos[qlwb] up to size 64. gcc-3.3.3 on i386's uses mov[lwb] for sizes up to 8, then stos[lwb] for all larger sizes. - the relevant change seems to be:
% Index: i386.c % =================================================================== % RCS file: /home/ncvs/src/contrib/gcc/config/i386/i386.c,v % retrieving revision 1.20 % retrieving revision 1.21 % diff -u -2 -r1.20 -r1.21 % --- i386.c 19 Jun 2004 20:40:00 -0000 1.20 % +++ i386.c 28 Jul 2004 04:47:35 -0000 1.21 % @@ -437,26 +502,36 @@ % ... % +const int x86_rep_movl_optimal = m_386 | m_PENT | m_PPRO | m_K6; % ...
Note that rep_movl is considered optimal on i386's but not on amd64's.
% @@ -10701,6 +11427,10 @@ % /* In case we don't know anything about the alignment, default to % library version, since it is usually equally fast and result in % - shorter code. */ % - if (!TARGET_INLINE_ALL_STRINGOPS && align < UNITS_PER_WORD) % + shorter code. % + % + Also emit call when we know that the count is large and call overhead % + will not be important. */ % + if (!TARGET_INLINE_ALL_STRINGOPS % + && (align < UNITS_PER_WORD || !TARGET_REP_MOVL_OPTIMAL)) % return 0; %
TARGET_REP_MOVL_OPTIMAL is x86_rep_movl_optimal modulo a mask. It is zero for amd64's, so 0 is returned for amd64's here unless you use -mfoo to set TARGET_INLINE_ALL_STRINGOPS. Returning 0 gives the library call instead of a stringop.
This is in i386_expand_clrstr(). There is an identical change in i386_expand_movstr() that gives library calls to memcpy() for (at least) copying structs.
Bruce _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"
