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87 lines
3.0 KiB
Markdown
87 lines
3.0 KiB
Markdown
<!--===- docs/RuntimeEnvironment.md
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Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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See https://llvm.org/LICENSE.txt for license information.
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SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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-->
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```{contents}
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---
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local:
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---
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```
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# Environment variables of significance to Fortran execution
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A few environment variables are queried by the Fortran runtime support
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library.
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The following environment variables can affect the behavior of
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Fortran programs during execution.
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## `DEFAULT_UTF8=1`
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Set `DEFAULT_UTF8` to cause formatted external input to assume UTF-8
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encoding on input and use UTF-8 encoding on formatted external output.
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## `FORT_CONVERT`
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Determines data conversions applied to unformatted I/O.
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* `NATIVE`: no conversions (default)
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* `LITTLE_ENDIAN`: assume input is little-endian; emit little-endian output
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* `BIG_ENDIAN`: assume input is big-endian; emit big-endian output
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* `SWAP`: reverse endianness (always convert)
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## `FORT_CHECK_POINTER_DEALLOCATION`
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Fortran requires that a pointer that appears in a `DEALLOCATE` statement
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must have been allocated in an `ALLOCATE` statement with the same declared
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type.
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The runtime support library validates this requirement by checking the
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size of the allocated data, and will fail with an error message if
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the deallocated pointer is not valid.
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Set `FORT_CHECK_POINTER_DEALLOCATION=0` to disable this check.
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## `FORT_FMT_RECL`
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Set to an integer value to specify the record length for list-directed
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and `NAMELIST` output.
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The default is 72.
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## `NO_STOP_MESSAGE`
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Set `NO_STOP_MESSAGE=1` to disable the extra information about
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IEEE floating-point exception flags that the Fortran language
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standard requires for `STOP` and `ERROR STOP` statements.
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## `FORT_TRUNCATE_STREAM`
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Set `FORT_TRUNCATE_STREAM=1` to make output to a formatted unit
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with `ACCESS="STREAM"` truncate the file when the unit has been
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repositioned via `POS=` to an earlier point in the file.
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This behavior is analogous to the implicit writing of an ENDFILE record
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when output takes place to a sequential unit after
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executing a `BACKSPACE` or `REWIND` statement.
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Truncation of a stream-access unit is common to several other
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compilers, but it is not mentioned in the standard.
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## `FORT_NO_EMPTY_ALLOCATION`
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Set `FORT_NO_EMPTY_ALLOCATION=1` to cause `ALLOCATE` statements
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fail when the allocated size is empty.
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## `FLANG_TRAMPOLINE_POOL_SIZE`
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Set `FLANG_TRAMPOLINE_POOL_SIZE` to an integer value to control the maximum
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number of runtime trampoline slots available when `-fsafe-trampoline` is
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enabled. Each slot consists of a small executable code stub (size varies by
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target; e.g. 32 bytes on x86-64 and AArch64) backed by a writable data entry.
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The default is 1024 slots, which is sufficient for typical Fortran
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programs. If more internal-procedure closures are alive simultaneously than
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the pool can hold, the runtime terminates with a diagnostic message that
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includes the current pool capacity.
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Example: `export FLANG_TRAMPOLINE_POOL_SIZE=4096`
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