Hojun-Cho
294f4c93fd
SysV §3.5.7 requires a variadic call to set AL = number of vector (XMM) regs used for the variable float args; the C callee gates its xmm-save-area stores on `test %al,%al`, so the old hardcoded XORQ AX,AX (AL=0) made va_arg(double) read garbage for any float-bearing C variadic call. Emit MOVQ $fi,AX (fi = the in-scope XMM cursor, ≤8); w6a has no MOVL-immediate encoding so MOVQ is the assemblable form and sets AL=fi identically. fi==0 keeps XORQ → byte-identical to pre-fix for no-float variadic calls. Runtime test 989_ffivariadic links a cc-compiled va_arg(double) fixture (zero relocs/undefined, w6l-linkable) and sweeps N=3/5/8 floats (N=2 is vacuous via stale-stack aliasing). C1 of the C-FFI-variadic align-up (USER ruling); C2 wwstage + C3 bodiless gate follow. ref/qbe/amd64/sysv.c:384. 454 green.
27 lines
639 B
C
27 lines
639 B
C
/*
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* C-FFI variadic test fixture (C1, catB-54). A va_arg(double) summer the
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* ww caller links against to prove the SysV AL=XMM-count fix: the callee
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* gates its xmm-save-area stores on `test %al,%al`, so a wrong AL makes
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* these va_arg(double) reads pull garbage.
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*
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* Built self-contained (zero relocs, zero undef syms) so w6l can link it
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* with no libc — verified via readelf -r / nm. Do not add any call that
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* pulls in a libc symbol.
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*/
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#include <stdarg.h>
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double
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fixture(long n, ...)
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{
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va_list ap;
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double s;
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long i;
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va_start(ap, n);
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s = 0;
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for(i = 0; i < n; i++)
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s += va_arg(ap, double);
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va_end(ap);
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return s;
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}
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