forked from Minki/linux
b0984c4370
In the microMIPS encoding some memory access instructions have their
immediate offset reduced to 12 bits only. That does not match the GCC
`R' constraint we use in some places to satisfy the requirement,
resulting in build failures like this:
{standard input}: Assembler messages:
{standard input}:720: Error: macro used $at after ".set noat"
{standard input}:720: Warning: macro instruction expanded into multiple instructions
Fix the problem by defining a macro, `GCC_OFF12_ASM', that expands to
the right constraint depending on whether microMIPS or standard MIPS
code is produced. Also apply the fix to where `m' is used as in the
worst case this change does nothing, e.g. where the pointer was already
in a register such as a function argument and no further offset was
requested, and in the best case it avoids an extraneous sequence of up
to two instructions to load the high 20 bits of the address in the LL/SC
loop. This reduces the risk of lock contention that is the higher the
more instructions there are in the critical section between LL and SC.
Strictly speaking we could just bulk-replace `R' with `ZC' as the latter
constraint adjusts automatically depending on the ISA selected.
However it was only introduced with GCC 4.9 and we keep supporing older
compilers for the standard MIPS configuration, hence the slightly more
complicated approach I chose.
The choice of a zero-argument function-like rather than an object-like
macro was made so that it does not look like a function call taking the
C expression used for the constraint as an argument. This is so as not
to confuse the reader or formatting checkers like `checkpatch.pl' and
follows previous practice.
Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com>
Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8482/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
28 lines
719 B
C
28 lines
719 B
C
/*
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* Copyright (C) 2004, 2007 Maciej W. Rozycki
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*
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* This file is subject to the terms and conditions of the GNU General Public
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* License. See the file "COPYING" in the main directory of this archive
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* for more details.
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*/
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#ifndef _ASM_COMPILER_H
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#define _ASM_COMPILER_H
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#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
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#define GCC_IMM_ASM() "n"
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#define GCC_REG_ACCUM "$0"
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#else
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#define GCC_IMM_ASM() "rn"
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#define GCC_REG_ACCUM "accum"
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#endif
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#ifndef CONFIG_CPU_MICROMIPS
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#define GCC_OFF12_ASM() "R"
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#elif __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
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#define GCC_OFF12_ASM() "ZC"
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#else
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#error "microMIPS compilation unsupported with GCC older than 4.9"
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#endif
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#endif /* _ASM_COMPILER_H */
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