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Refactor ABI wrappers to not rely on --wrap
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,52 @@ | ||
| # Starboard Modular ABI Wrappers | ||
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| This directory contains code that will handle translations of data types across | ||
| ABI boundaries. | ||
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| These wrappers are used in modular builds (including Evergreen). They are needed | ||
| to handle dealing with differences in platform-specific toolchain types and | ||
| musl-based types. For example, the `struct timespec` and `struct timeval` types | ||
| may contain differently sized member fields and when the caller is Cobalt code | ||
| compiled with musl it will provide argument data that needs to be adjusted when | ||
| passed to platform-specific system libraries. | ||
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| To do this adjustment across compilation toolchains, there are 2 sets of files | ||
| in this directory that will be compiled in either the Cobalt toolchain or the | ||
| Starboard plaform-specific toolchain: | ||
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| * `cobalt_layer_posix_XYZ_abi_wrappers.cc` - these are compiled only in the | ||
| Cobalt toolchain for modular builds (excluding Evergreen). The logic in | ||
| these files simply defines the API we want to wrap and re-calls an external | ||
| function named `__abi_wrap_XYZ` using the exact same parameter and return | ||
| value types. This is simply to get the libcobalt.so to not link against | ||
| the glibc implementations and instead rely on an external implementation | ||
| that will be defined in libstarboard.so. Similar logic is done specifically | ||
| for Evergreen in exported_symbols.cc, since we have a custom ELF loader in | ||
| that case to handle remapping the functions. | ||
| * `starboard_layer_posix_XYZ_abi_wrappers.{h,cc}` - these are compiled only | ||
| in the Starboard platform-specific toolchain for modular builds (including | ||
| Evergreen). The header files define corresponding musl-compatible types | ||
| (copying definitions provided in //third_party/musl/include/alltypes.h.in) | ||
| for the cases where data types are not guaranteed to match across ABI | ||
| boundaries. These files then define the implementation of the | ||
| `__abi_wrap_XYZ` functions, which will be called from the Cobalt layer. | ||
| Since these functions are being implemented/compiled in the Starboard | ||
| layer, they will rely on the platform-specific toolchain to get the | ||
| platform-specific type definitions from the system headers (e.g. <time.h>). | ||
| The implementations will handle doing data type conversions across the | ||
| ABI boundary (both for parameters and return types). | ||
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| To help illustrate how this works, we can use the POSIX function `clock_gettime` | ||
| as an example. When we build modularly, the following table shows how the | ||
| symbols would look using a tool like `nm`: | ||
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| ``` | ||
| libstarboard.so: | ||
| U clock_gettime@GLIBC_2.17 (undefined reference to platform library) | ||
| T __abi_wrap_clock_gettime (concrete definition of ABI wrapper function) | ||
| libcobalt.so | ||
| U __abi_wrap_clock_gettime (undefined reference to the Starboard wrapper) | ||
| t clock_gettime (concrete definition that calls __abi_wrap_*) | ||
| ``` |
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starboard/shared/modular/cobalt_layer_posix_mmap_abi_wrappers.cc
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| // Copyright 2024 The Cobalt Authors. All Rights Reserved. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
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| #if SB_API_VERSION >= 16 | ||
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| #include <sys/mman.h> | ||
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| extern "C" { | ||
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| void* __abi_wrap_mmap(void* addr, | ||
| size_t len, | ||
| int prot, | ||
| int flags, | ||
| int fildes, | ||
| off_t off); | ||
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| void* mmap(void* addr, size_t len, int prot, int flags, int fildes, off_t off) { | ||
| return __abi_wrap_mmap(addr, len, prot, flags, fildes, off); | ||
| } | ||
| } | ||
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| #endif // SB_API_VERSION >= 16 |
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