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Diffstat (limited to 'lib/arm/switchu8.S')
| -rw-r--r-- | lib/arm/switchu8.S | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/lib/arm/switchu8.S b/lib/arm/switchu8.S new file mode 100644 index 000000000000..faffddb50c1e --- /dev/null +++ b/lib/arm/switchu8.S @@ -0,0 +1,43 @@ +//===-- switch.S - Implement switch* --------------------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// + +#include "../assembly.h" + +// +// When compiling switch statements in thumb mode, the compiler +// can use these __switch* helper functions The compiler emits a blx to +// the __switch* function followed by a table of displacements for each +// case statement. On entry, R0 is the index into the table. The __switch* +// function uses the return address in lr to find the start of the table. +// The first entry in the table is the count of the entries in the table. +// It then uses R0 to index into the table and get the displacement of the +// address to jump to. If R0 is greater than the size of the table, it jumps +// to the last entry in the table. Each displacement in the table is actually +// the distance from lr to the label, thus making the tables PIC. + + + .text + .syntax unified + +// +// The table contains unsigned byte sized elements which are 1/2 the distance +// from lr to the target label. +// + .align 2 +DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switchu8) + ldrb ip, [lr, #-1] // get first byte in table + cmp r0, ip // compare with index + ldrbcc r0, [lr, r0] // get indexed byte out of table + ldrbhs r0, [lr, ip] // if out of range, use last entry in table + add ip, lr, r0, lsl #1 // compute label = lr + element*2 + bx ip // jump to computed label + + // tell linker it can break up file at label boundaries + .subsections_via_symbols + |