FreeCalypso > hg > freecalypso-tools
annotate toolchain/binutils-patches/elf32-arm.patch @ 995:74024eb17e04
fc-loadtool help: improve language regarding 16 MiB flash chips
In FC project history, 16 MiB flash originally meant Pirelli DP-L10.
Then we got FCDEV3B with the same flash (our own design), but now we are
discovering more Calypso devices that used such large flash, both late
Calypso era (Sony Ericsson K2x0) as well as much earlier ones (FIC FLUID
devices.txt file with 2004 dates, Leonardo+ rev 5). Hence we need to
migrate to more generic or neutral language in associated documentation,
without giving elevated status to specific examples that drove our
early project history.
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sun, 03 Dec 2023 21:11:12 +0000 |
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1 # The present patch to the ARM ELF linking code in binutils (made against |
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2 # binutils-2.21.1a) is a hack that affects the generation of Thumb->ARM |
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3 # call veneers. The binutils linker can make these veneers in two forms: |
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4 # |
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5 # "Short" "Long" |
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6 # (16-bit) bx pc (16-bit) bx pc |
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7 # (16-bit) nop (16-bit) nop |
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8 # (32-bit) b dest (32-bit) ldr pc, [pc, #-4] |
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9 # (32-bit) .long target |
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10 # |
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11 # For code that's going to run on the Calypso ARM7 processor, the |
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12 # "short" form is the one we want: because of the way the address space |
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13 # is laid out, the range of an ARM branch instruction will always be |
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14 # sufficient for us, whereas the long version is more costly in terms |
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15 # of the number of cycles required, especially when executing from |
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16 # external memory. |
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17 # |
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18 # Unfortunately, the code which decides between these two forms |
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19 # (located in the arm_type_of_stub() function in bfd/elf32-arm.c) |
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20 # is broken. The original code (which you can see below in the |
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21 # "before" part of the patch hunk) exhibits two problems: |
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22 # |
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23 # 1. The distance that matters here is not from the original |
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24 # call point to the destination, but from the stub to |
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25 # the destination - and in this function we don't know |
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26 # where the stub will end up. |
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27 # |
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28 # 2. Because it's an ARM branch, the limits should be |
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29 # ARM_MAX_[BF]WD_BRANCH_OFFSET, not the THM_ ones. |
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30 # |
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31 # The 2nd problem would be trivial to fix, but the 1st one |
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32 # much less so: this function doesn't know where the stub |
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33 # will end up, and considering that for the present purpose |
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34 # of the FreeCalypso project always emitting the "short" |
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35 # version would be perfect, there is no justification for |
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36 # expending the time and effort to restructure the linker |
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37 # to do the proper relaxation for the case at hand. |
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38 # |
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39 # Therefore, the patch we apply is a hack: we simply force the |
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40 # use of the "short" form unconditionally. |
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41 |
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42 *** elf32-arm.c Wed May 11 07:29:12 2011 |
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43 --- elf32-arm-patched.c Mon Aug 19 03:24:38 2013 |
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44 *************** |
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45 *** 3203,3211 **** |
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46 : arm_stub_long_branch_v4t_thumb_arm); |
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47 |
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48 /* Handle v4t short branches. */ |
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49 ! if ((stub_type == arm_stub_long_branch_v4t_thumb_arm) |
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50 ! && (branch_offset <= THM_MAX_FWD_BRANCH_OFFSET) |
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51 ! && (branch_offset >= THM_MAX_BWD_BRANCH_OFFSET)) |
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52 stub_type = arm_stub_short_branch_v4t_thumb_arm; |
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53 } |
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54 } |
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55 --- 3203,3209 ---- |
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56 : arm_stub_long_branch_v4t_thumb_arm); |
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57 |
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58 /* Handle v4t short branches. */ |
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59 ! if (stub_type == arm_stub_long_branch_v4t_thumb_arm) |
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60 stub_type = arm_stub_short_branch_v4t_thumb_arm; |
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61 } |
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62 } |