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frv gas: align code with nops
- From: Alexandre Oliva <aoliva at redhat dot com>
- To: binutils at sources dot redhat dot com
- Date: 05 May 2004 23:57:47 -0300
- Subject: frv gas: align code with nops
- Organization: Red Hat Global Engineering Services Compiler Team
We currently use the all-zero bit pattern to pad code for alignment,
but that's bad, for the reasons explained in the comments below. Ok
to install? Ok for 2.15? Tested on i686-pc-linux-gnu-x-frv-uclinux.
Index: gas/ChangeLog
from Alexandre Oliva <aoliva@redhat.com>
* config/tc-frv.h (MAX_MEM_FOR_RS_ALIGN_CODE): New.
(HANDLE_ALIGN): New.
Index: gas/config/tc-frv.h
===================================================================
RCS file: /cvs/uberbaum/gas/config/tc-frv.h,v
retrieving revision 1.5
diff -u -p -r1.5 tc-frv.h
--- gas/config/tc-frv.h 6 May 2004 02:46:45 -0000 1.5
+++ gas/config/tc-frv.h 6 May 2004 02:56:17 -0000
@@ -86,3 +86,44 @@ extern long md_pcrel_from_section PARAMS
for any relocations that pic won't support. */
#define tc_frob_file() frv_frob_file ()
extern void frv_frob_file PARAMS ((void));
+
+/* We don't want 0x00 for code alignment because this generates `add.p
+ gr0, gr0, gr0' patterns. Although it's fine as a nop instruction,
+ it has the VLIW packing bit set, which means if you have a bunch of
+ them in a row and attempt to execute them, you'll exceed the VLIW
+ capacity and fail. This also gets GDB confused sometimes, because
+ it won't set breakpoints in instructions other than the first of a
+ VLIW pack, so you used to be unable to set a breakpoint in the
+ initial instruction of a function that followed such
+ alignment-introduced instructions.
+
+ We could have arranged to emit `nop' instructions (0x80880000),
+ maybe even VLIW-pack sequences of nop instructions as much as
+ possible for the selected machine type, just in case the alignment
+ code actually happens to run, but this is probably too much effort
+ for little gain. This code is not meant to be run anyway, so just
+ emit nops. */
+#define MAX_MEM_FOR_RS_ALIGN_CODE (3 + 4)
+#define HANDLE_ALIGN(FRAGP) do \
+ if ((FRAGP)->fr_type == rs_align_code) \
+ { \
+ valueT count = ((FRAGP)->fr_next->fr_address \
+ - ((FRAGP)->fr_address + (FRAGP)->fr_fix)); \
+ unsigned char *dest = (FRAGP)->fr_literal + (FRAGP)->fr_fix; \
+ if ((count & 3) != 0) \
+ { \
+ memset (dest, 0, (count & 3)); \
+ (FRAGP)->fr_fix += (count & 3); \
+ dest += (count & 3); \
+ count -= (count & 3); \
+ } \
+ if (count) \
+ { \
+ (FRAGP)->fr_var = 4; \
+ *dest++ = 0x80; \
+ *dest++ = 0x88; \
+ *dest++ = 0x00; \
+ *dest++ = 0x00; \
+ } \
+ } \
+ while (0)
--
Alexandre Oliva http://www.ic.unicamp.br/~oliva/
Red Hat Compiler Engineer aoliva@{redhat.com, gcc.gnu.org}
Free Software Evangelist oliva@{lsd.ic.unicamp.br, gnu.org}