On Mon, 2012-04-16 at 12:41 -0700, Juli Mallett wrote: > On Mon, Apr 16, 2012 at 02:38, Andrew Turner <and...@freebsd.org> wrote: > > Log: > > Replace the C implementation of __aeabi_read_tp with an assembly version. > > This ensures we follow the ABI by preserving registers r1-r3. > > > +ENTRY(__aeabi_read_tp) > > + ldr r0, .Larm_tp_address > > + ldr r0, [r0] > > + RET > > + > > +.Larm_tp_address: > > + .word ARM_TP_ADDRESS > > + > > Why is this indirection required? Can't you just use ARM_TP_ADDRESS > instead of loading it from data? Also, is our convention for ARM to > use END() with ENTRY() or not?
It used to be possible to directly load ARM_TP_ADDRESS into a register when it had a cleverly-crafted value that made use of ARM's ability to encode a constant value into an instruction if it can be expressed as an 8-bit value shifted by anything up to 31 bits. (iirc, it used to be 0xe0000000). At some point that address became a problem for someone and it got changed to a value which can no longer be encoded within the instruction. The alternative is to load it with a single instruction by using a pc-relative address, or use a series of load-and-shift instructions to form the new more complex constant. Ick. -- Ian _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
