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Fix code generation error in gcc6809 It turned out that under some circumstances, the gcc optimizer would select an instruction sequence that had the sense of a branch inverted. It seems this was due to a particular instruction pattern included in the machine description not being quite right with respect to how the condition codes were tracked. Removing that instruction pattern seems to fix things (subtraction with the arguments reversed). gcc seems to be smart enough to figure out how to reorganize code to work without this reversed sense subtraction and then do the right thing.
author William Astle <lost@l-w.ca>
date Thu, 24 Mar 2016 20:07:20 -0600
parents 8222f30a0781
children d7b7004b0883
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 These files are extra utility type scripts that can be used for various
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2 purposes.
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3
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4 as
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5
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6 This is a sort of front-end script that makes lwasm look approximately like
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7 gnu as which is useful for using lwasm as a backend to gcc. You may need to
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8 edit it to make it work fully.
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9
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10 ld
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11
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12 Similar to the "as" script above except for lwlink.
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15 ar
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16
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17 Similar to the "as" script above except for lwar.
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18
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19 gcc6809lw-*.patch
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21 These are patches to the main gcc source distribution for specific releases.
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22 The last number after the dash is a patch level for the specific patch. It
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23 is worth noting that a patch for a particular minor version of GCC may work
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24 with later minor versions in the same release sequence. That is, a patch
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25 for 4.6.1 might work with 4.6.4. These are different to the official
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26 gcc6809 releases in the following ways. First, all the source for as-6809
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27 is removed. Also, the special "helper" makefile and directory is removed.
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28 Also, as of this writing, the latest "official" release was for gcc 4.3.4
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29 which does not build on 64 bit linux.
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31 In the event you have used the "official" gcc6809 with the default as6809
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32 assembler that comes with it, you should be aware that while lwasm is mostly
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33 compatible with it syntax wise, there are differences, particularly in
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34 pseudo operations and source line syntax (most notably that you must have
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35 whitespace preceeding assembler directives and instructions). You will
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36 likely not run into these unless you are using inline asm. Refer to the
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37 lwtools documentation for the specific line format required by lwasm.
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38
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39 It is worth noting that neither gcc6809 nor lwtools comes with a standard C
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40 library.
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41
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42 It is also worth noting that for many projects, it will be more flexible to
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43 invoke lwlink directly rather than using the ld script or gcc as a front
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44 end. See the lwtools documentation for details on using lwlink.
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46 To use these scripts, you really need to understand how to build a gcc as a
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47 cross compiler. The basics are that you put the as, ld, and ar scripts
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48 whereever you plan to put your cross-development binaries. Then, when
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49 building the cross compiler, you tell it where the scripts are.
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51 Please note that the following recipe is an example only. If you are
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52 planning to install multiple instances of gcc6809 for different targets, you
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53 will most certainly need to modify the steps below. Providing a complete
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54 understanding of building a gcc toolchain for cross compilation is well
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55 beyond the scope of this document.
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56
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57 The following works for a single installation.
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59 1. Install the ar, as, and ld scripts named m6809-unknown-{as,ar,ld} in a
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60 directory in your path, say /usr/local/coco/bin/.
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62 2. Make symbolic links to /bin/true for similarly named nm, objdump, ranlib,
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63 and strip in the same directory Some of these may not be necessary.
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64
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65 3. Unpack gcc and apply the gcc6809 patch. The gcc6809lw* patch file
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66 in this directory is known to work with these instructions.
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68 4. Make sure /usr/local/coco/bin is in your PATH
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70 5. Make sure "." is NOT in your path or is at the END of PATH. If you have
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71 gazillions of errors pop up compiling "gemodes.c", this is your problem.
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73 6. In a directory (other than the gcc source, say "gcc-build" at the same
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74 level as the main gcc directory, do (assuming gcc 4.3.4):
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75
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76 configure --enable-languages=c --target=m6809-unknown \
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77 --program-prefix=m6809-unknown- --enable-obsolete \
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78 --srcdir=../gcc-4.3.4 --disable-threads --disable-nls \
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79 --disable-libssp --prefix=/usr/local/coco \
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80 --with-as=/usr/local/coco/bin/m6809-unknown-as \
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81 --with-ld=/usr/local/coco/bin/m6809-unknown-ld \
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82 --with-ar=/usr/local/coco/bin/m6809-unknown-ar
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83
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84 NOTE: the last three are required to prevent selection of the wrong binutils
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85 programs at runtime.
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86
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87 --with-sysroot might be useful if you have a C library involved.
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88
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89 7. Run "make". If errors appear, troubleshoot.
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90
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91 8. Run "make install". Note that you will have to have your PATH variable
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92 for "root" set up correctly if your install prefix requires root privileges.
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93
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94 The above is WOMM certified. YMMV.
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95
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96 NOTES ABOUT SPECIFIC PATCHES
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97 ============================
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98
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99 gcc6809lw-4.6.4-2.patch
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100
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101 This patch essentially disables the "soft registers". These were causing
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102 problems leading to compiler crashes. Removing the "t" constraint from
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103 the instruction patterns allowed various issues to go away. It is not clear
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104 if the original reasoning behind these soft registers is even valid any
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105 more.
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106
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107 Also fixes a clearly incorrect comparision when determining if a constant
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108 fits in 16 bits. For clarity, both the 8 bit and 16 bit comparisons are
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109 replaced with straight forward range comparisons rather than the excessively
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110 clever scheme that was present before.
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111
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112 gcc6809lw-4.6.4-3.patch
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113
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114 This is identical to the -2 version except it fixes the crt0.S file so it
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115 builds properly with the --pragma=newsource option. In fact, it never did
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116 build properly due to spaces in operands anyway. However, since gcc6809
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117 doesn't come with a C library, it hasn't proved to be an issue.
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118
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119 Patches to provide a proper crt0.S file based around the actual way lwtools
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120 works will be considered.
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121
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122 It's also worth noting that there are features inherited from previous
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123 versions of gcc6809 that are not properly supported by these patches. In
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124 particular, banking and "far calls" are not supported because there are no
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125 targets supported by lwtools that do anything meaningful in the face of such
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126 things. Patches to clean that up are also welcome. Either to do something
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127 meaningful or to remove such features entirely.
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128
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129 gcc6809lw-4.6.4-4.patch
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130
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131 This is identical to the -3 version except it fixes a code generation bug
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132 that showed up under optimization. It would result in the sense of a branch
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133 following a subtraction being inverted for whatever reason. This change
b4d0eafc5bfe Fix code generation error in gcc6809
William Astle <lost@l-w.ca>
parents: 415
diff changeset
134 seems to fix that.