diff options
Diffstat (limited to 'gas/NOTES')
| -rw-r--r-- | gas/NOTES | 47 |
1 files changed, 6 insertions, 41 deletions
@@ -5,23 +5,16 @@ PORTING: Sorry, no description of the interfaces is written up yet. Look at existing back ends and work from there. -New hosts: If your host system has a strange header file setup, create a -config/ho-foo.h file for it and include the appropriate header files or -definitions there. If your host has a broken compiler, or some broken macros -in header files, create a host-specific file and repair the damage there. -(See, for example, ho-rs6000.h. The "assert" macro on that system doesn't work -right, and a flag is set to rewrite an expression in tc-m68k.c that the native -compiler mis-compiles.) - -New target formats: Look at the BFD_ASSEMBLER code. The a.out code might be a -fair example. There are no "good" examples yet, unfortunately, nor any good -documentation of the changes. +New hosts: The configure script, which is generated by autoconf, +should handle all host specific configuration. + +New target formats: Look at the BFD_ASSEMBLER code. The a.out or ELF +code might be a fair example. There are no "good" examples yet, +unfortunately, nor any good documentation of the changes. New target processors: Check first to see if the BFD_ASSEMBLER interface is supported by the file format code you need to use. -New environments: ??? - DOCUMENTATION: The internals of gas need documenting. @@ -45,10 +38,6 @@ non-BFD_ASSEMBLER version often has multiple conditional tests inside it for various processors or formats. As the various targets get converted over, these will gradually go away. -As of the moment I'm editing this file, only the "sun4" and "decstation-bsd" -targets can really use the BFD code. Other back ends still need merging or -touching up. - TO DO: Remove DONTDEF code, commented-out code. @@ -105,30 +94,6 @@ Torbjorn Granlund <tege@cygnus.com> writes, regarding alpha .align: since these two instructions can dual-issue. Since .align is ued a lot by gcc, it is an important optimization. -Torbjorn Granlund <tege@cygnus.com> writes, regarding i386/i486/pentium: - - In a new publication from Intel, "Optimization for Intel's 32 bit - Processors", they recommended code alignment on a 16 byte boundary if that - requires less than 8 bytes of fill instructions. The Pentium is not - affected by such alignment, the 386 wants alignment on a 4 byte boundary. - It is the 486 that is most helped by large alignment. - - Recommended nop instructions: - 1 byte: 90 xchg %eax,%eax - 2 bytes: 8b c0 movl %eax,%eax - 3 bytes: 8d 76 00 leal 0(%esi),%esi - 4 bytes: 8d 74 26 00 leal 0(%esi),%esi - 5 bytes: 8b c0 8d 76 00 movl %eax,%eax; leal 0(%esi),%esi - 6 bytes: 8d b6 00 00 00 00 leal 0(%esi),%esi - 7 bytes: 8d b4 26 00 00 00 00 leal 0(%esi),%esi - - Note that `leal 0(%esi),%esi' has a few different encodings... - - There are faster instructions for certain lengths, that are not true nops. - If you can determine that a register and the condition code is dead (by - scanning forwards for a register that is written before it is read, and - similar for cc) you can use a `incl reg' for a 3 times faster 1 cycle nop... - (From old "NOTES" file to-do list, not really reviewed:) fix relocation types for i860, perhaps by adding a ref pointer to fixS? |