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annotate Firmware-deblobbing @ 33:7aed57fc1928

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FC-modem-family article fully rewritten for the new reality of FC Tango modules
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 28 Sep 2020 00:48:17 +0000
parents f68ca40fa5c1
children 14b8e532c966
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1 The state of blobs vs. blob-free firmware in FreeCalypso
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2 ========================================================
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3
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4 As of 2019, we have 3 different firmware versions for Standard Modem
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5 functionality:
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6
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7 * Magnetite hybrid is the current production firmware version. The only blobs
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8 are Nucleus, OSL and OSX glue components of GPF, and TI's proprietary TMS470
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9 compiler. Everything other than Nucleus and OSL/OSX is compiled from source,
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10 but the compiler is TI's proprietary TMS470. The same Magnetite source tree
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11 also supports other configurations (maintained only for regression testing)
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12 which have more blobs, as well as handset configurations which are currently
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13 frozen for lack of suitable development hardware.
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14
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15 * Selenite-470 is FC Selenite built with TI's TMS470 compiler: all code is
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16 compiled from source, no blobs other than the compiler and its RTS library
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17 (libc/libgcc equivalent). The blob version of Nucleus is replaced with a
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18 different (slightly newer) version in full source form, while the blob
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19 versions of OSL and OSX glue components have been replaced with reconstructed
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20 sources, i.e., a reconstruction based on disassembly. This fw version is
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21 currently considered experimental, not cleared for production, and the reason
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22 is OSL/OSX: the reconstruction is of uncertain correctness and known to be
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23 incomplete.
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24
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25 * Selenite-gcc is FC Selenite built with gcc. This version has no blobs
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26 whatsoever (there is no support in the gcc+binutils toolchain for TI's TMS470
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27 ABI, thus it is physically impossible to include any of TI's COFF blobs in
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28 the link), and it is built with a FLOSS compiler. However, it is even more
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29 experimental and not-for-production than Selenite-470: not only is the OSL/OSX
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30 issue still there, but there is also widespread breakage from the use of a
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31 different compiler which was never anticipated by the original developers.
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32 The old FC Citrine firmware (unmaintained since 2016) also suffers from all
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33 of the same problems, plus additional ones, and therefore should not be
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34 considered at all.
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35
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36 When it comes to the firmware, right now those OSL and OSX glue components of
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37 GPF form the biggest bone in our collective throat. Just 10 C source files are
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38 missing:
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39
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40 os_com.c
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41 os_drv.c
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42 os_evt.c
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43 os_isr.c
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44 os_mem.c
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45 os_mis.c
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46 os_pro.c
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47 os_sem.c
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48 os_tim.c
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49 osx.c
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50
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51 If we can ever find these 10 missing files (does not even need to be exactly
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52 the same version as in TCS211 GPF), then Selenite-470 would immediately become
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53 the new production firmware replacing Magnetite (the Nucleus change isn't the
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54 problem, it's OSL and OSX), and the way would be cleared to begin work on
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55 bringing Selenite-gcc up to par. But in the absence of these 10 files, the
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56 following two interlocking problems get in the way of FC Selenite:
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57
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58 1) I (Mother Mychaela) am not willing to skip Selenite-470 and jump directly to
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59 Selenite-gcc, as doing so would violate the fundamental principle of
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60 incrementality: we need to be making one small change at a time, requiring
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61 full stability after each incremental change before going to the next.
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62
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63 2) I am not able to produce a reconstructed C source for certain parts of OSL
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64 which would result in correct object code when compiled with TMS470: the
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65 issue is potential race conditions in the OSL timer code. The existing COFF
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66 object code avoids the race, I can produce C code for compilation with gcc
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67 which also avoids the race, but I don't know the requisite magic for C code
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68 to be compiled with TMS470.
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69
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70 At this point you are going to ask - OK, so what do we do if we can't find
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71 those 10 missing files? The Mother's current plan is as follows: if these 10
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72 files are still missing when we get our handset UI development board built, I
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73 will create a third firmware source tree (not Magnetite, not Selenite, but to
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74 be named after some other mineral) with the following key properties:
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75
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76 * Just like Selenite, it will be hybrid only, no legacy blob-laden
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77 configurations;
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78
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79 * Both modem and handset configurations will be included;
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80
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81 * The compiler will be TMS470 - sorry, no gcc;
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82
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83 * The version of Nucleus will be the new source-enabled one, same as Selenite;
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84
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85 * I will do some careful surgery on the OSL/OSX blobs to make them work with
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86 the new version of Nucleus.
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87
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88 The result of these listed key properties is that the new firmware tree will
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89 have blobs for OSL and OSX and will use the TMS470 compiler as required by
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90 these blobs, but absolutely everything else will be source-enabled. This
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91 situation will then persist until someone can wave a few million dollars in
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92 front of TI to convince their execs to direct their archivists to dig up the 10
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93 missing files, or until the world civilization collapses into a Mad Max world,
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94 allowing us to seize those archives with a Spetsnaz unit without police
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95 interference.
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96
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97 Special modem applications
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98 ==========================
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99
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100 The above plan states that the third firmware source tree will be created as
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101 described if the original OSL and OSX source files are still missing when we
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102 get our handset UI development board built. The reason for this coupling is
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103 that when we get this UIDB built, the floodgates will open for intensive
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104 handset UI development. The latter work will need to be done without the
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105 clutter of Magnetite, yet Selenite is blocked by the lack of the 10 missing
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106 files - hence the case for the third firmware source tree as described above.
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107
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108 Alternatively, a third fw source tree similar to the one described (but perhaps
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109 without the handset configuration) can be created if someone commissions
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110 significant work on modem firmware, work that is significant enough to call for
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111 a source tree that is as stable as Magnetite, but free of the clutter.
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112
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113 cdginc header files
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114 ===================
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115
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116 Another area of deblobbing that hasn't been done yet, but can be done when and
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117 if a serious need arises, is the cdginc header file set. The cdginc files which
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118 are currently used for our hybrid config aren't blobs in the strict sense: they
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119 are C header files included by the sources being recompiled, but they have been
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120 auto-generated (from true human-editable sources which we do have) by a tool
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121 (ccdgen) which currently exists only as a Windows binary sans source.
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122
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123 If anyone needs to make changes to cdginc, the proper course of action should
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124 be to hire a Windows reverser to reverse ccdgen.exe and to produce a perfect
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125 form, fit and function replacement.