Only mangle the capability qualifier for pointers in the hybrid ABI #390
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In the purecap ABI the default pointer representation is capabilities, so there is no need to add the qualifier to the name mangling. In fact this can result in difficult-to-debug failures since e.g. version scripts will no longer export the correct symbols. This problem was discovered in libcxxrt: the type_info objects for pointer types (e.g. "char*"/"char* const") were not exported from the purecap library, resulting in linker failures for C++ programs that use RTTI. Having all pointers mangled was useful to catch incorrect linker paths before I added CHERI support to LLD since C++ programs would fail to link due to missing symbols. However, we now emit errors when attempting to link purecap and non-purecap libraries so this is no longer useful. Since the capability mangling is now only used in hybrid mode, I also changed the mangling to U12__capability: `void test(void *__capability)` now mangles as _Z4testU12__capabilityPv instead of _Z4testU3capPv and llvm-cxxfilt demangles it to `test(void* __capability)` instead of `test(void* cap)`.
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This generally makes sense. I've not reviewed the contents of the change.
I've occasionally thought that it might be useful to be able to call pure-cap functions from hybrid code and this would break that, but I think I'm OK with that being a different ABI if that ever turns out to be useful.
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I think it's fine to just have a flag day on the dev branch. We don't have that much C++ code. |
Some kind of attribute/pragma/extern (like |
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This has been merged to dev. |
In the purecap ABI the default pointer representation is capabilities, so
there is no need to add the qualifier to the name mangling. In fact this
can result in difficult-to-debug failures since e.g. version scripts will
no longer export the correct symbols. This problem was discovered in
libcxxrt: the type_info objects for pointer types (e.g. "char*"/"char* const")
were not exported from the purecap library, resulting in linker failures
for C++ programs that use RTTI.
Having all pointers mangled was useful to catch incorrect linker paths
before I added CHERI support to LLD since C++ programs would fail to link
due to missing symbols. However, we now emit errors when attempting to
link purecap and non-purecap libraries so this is no longer useful.
Since the capability mangling is now only used in hybrid mode, I also
changed the mangling to U12__capability:
void test(void *__capability)now mangles as _Z4testU12__capabilityPvinstead of _Z4testU3capPv and llvm-cxxfilt demangles it to
test(void* __capability)instead oftest(void* cap).This should be a better fix than CTSRD-CHERI/cheribsd#421
This is a flag day for all purecap C++ code but we should't have too much of it. Not sure if we should combine that with other flag days?