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Workaround WSL misconfiguring the x87 FPU

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Justine Tunney 2022-11-02 02:17:14 -07:00
parent f44d88707e
commit d6ff4c754e
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2 changed files with 26 additions and 19 deletions
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26
libc/runtime/cosmo.S
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@ -44,6 +44,32 @@ cosmo: push %rbp
mov %eax,%r12d
#endif /* SYSDEBUG */
// Windows always initializes FPU to douuble precision.
// WSL breaks Linux ABI by initializing FPU to double precision.
// This code makes long double long again.
//
// @see System V Application Binary Interface NexGen32e Architecture
// Processor Supplement, Version 1.0, December 5th, 2018
// Section 3.4.1: Initial Stack and Register State
fldcw 1f(%rip)
.rodata
.align 2
// 8087 FPU Control Word
// IM: Invalid Operation ───────────────┐
// DM: Denormal Operand ───────────────┐│
// ZM: Zero Divide ───────────────────┐││
// OM: Overflow ─────────────────────┐│││
// UM: Underflow ───────────────────┐││││
// PM: Precision ──────────────────┐│││││
// PC: Precision Control ───────┐ ││││││
// {float,∅,double,long double}│ ││││││
// RC: Rounding Control ──────┐ │ ││││││
// {even, →-∞, →+∞, →0} │┌┤ ││││││
// ┌┤││ ││││││
// d││││rr││││││
1: .short 0b00000000000000000001101111111
.previous
#ifdef __FAST_MATH__
push %rax
stmxcsr (%rsp)