| liushuyu | ahasenack: so there seems to be an issue with the unaligned memory access on arm devices when building gambas3. I found the workaround for this issue: make GCC generate full-length ARM code instead of Thumb/Thumb2 compressed code on armhf | 00:03 |
|---|---|---|
| liushuyu | ... with: export DEB_CFLAGS_MAINT_APPEND = -marm and export DEB_CXXFLAGS_MAINT_APPEND = -marm | 00:03 |
| ahasenack | that's way over my head | 00:03 |
| ahasenack | and which gcc? gcc-11, or without that change to d/rules, using the normal gcc? | 00:04 |
| liushuyu | ahasenack: This works with any version of GCC | 00:04 |
| liushuyu | I think you want to use the default GCC (which is GCC 13) | 00:04 |
| ahasenack | I would prefer that, yes | 00:04 |
| liushuyu | ... because poppler still needs a C++20 capable compiler | 00:05 |
| ahasenack | and does armel still need clang then? Or can it use the same trick? | 00:05 |
| liushuyu | ahasenack: I am unsure what happened with armel, but I guess it can use the same trick, since Clang generates ARM-mode code by default on Ubuntu | 00:06 |
| liushuyu | The full story is this: ARM devices (prior to aarch64), requires aligned memory access (usually needs to be aligned on the "word boundary", in armhf situation, one word = 32 bit). gambas3 has this bright idea where it reads the file using mmap() ... | 00:08 |
| ahasenack | but that used to be a runtime error, no? misaligned memory access | 00:08 |
| ahasenack | sigbus iirc | 00:09 |
| sarnold | sigbus, depending upon architecture | 00:09 |
| ahasenack | I haven't found the build error in the logs | 00:09 |
| liushuyu | ahasenack: well, it actually happened during the build, but the make flags hid the errors | 00:09 |
| sarnold | arm it was an implementation choice, some processors could cope, others couldn't, and some could only cope in 32bit or in 64bit mode, something like that .. | 00:09 |
| liushuyu | gambas3 used a hack to remove the print out | 00:10 |
| sarnold | in any event, any program doing unaligned access ought to be fixed | 00:10 |
| sarnold | switch pointer assignments to memcpy :( | 00:10 |
| liushuyu | ... (cont'd) mmap basically tells the kernel to map the specified file description into memory and treat as a part of the memory space. However, gambas3 read the file by bytes (not by words), which generates an unaligned access | 00:11 |
| liushuyu | ... (cont'd) unknown identifier issue was because their Makefile was so bad that did not handle the error correctly and let the build continue | 00:12 |
| ahasenack | can we fix that instead? Do you know where it's happening? And how about changing the invocation commands to not hide the errors, and stop when they happen? | 00:12 |
| liushuyu | sarnold: In aarch64, ARM provided a way to allow unaligned memory access, so this issue does not exist on arm64 | 00:12 |
| sarnold | liushuyu: I think our builders did sigbus on it though, heh | 00:13 |
| liushuyu | (see ARM reference manual ARM DDI 0487F.c ID072120 page E2-4044) | 00:14 |
| liushuyu | ahasenack: It's kind of problematic to fix, due to how gambas3 handles file I/O (it expect the kernel to map the file into the memory, and all the downstream functions just operate on the pointer that points to the virtual address | 00:16 |
| liushuyu | (If you want to hear another horror story about a certain package, I do have another recent one, mentioned very briefly on my +1 report) | 00:18 |
| ahasenack | not really, it's 21h20 here now :) | 00:19 |
| sarnold | that's firmly into weekend territory! | 00:19 |
| ahasenack | just that 3.19.0-2ubuntu10 built on armhf before, perhaps with LocutusOfBorg's gcc-11 patch | 00:19 |
| ahasenack | https://launchpad.net/ubuntu/+source/gambas3/3.19.0-2ubuntu10 | 00:19 |
| ahasenack | and, of course, previous poppler | 00:19 |
| liushuyu | ahasenack: I know, it's code generation fengshui, where GCC so happens to not generate a certain instruction that requires hard memory alignment | 00:21 |
| liushuyu | ... but newer GCC does generate this instruction (LDRD, Load Register Dual instruction) very often to optimize memory loads (since it can read 8 bytes at a time on a 32-bit system) | 00:22 |
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