Passing long double args on 32-bit SPARC violates ABI · Issue #41838 · llvm/llvm-project (original) (raw)

Extended Description

I'm current working to fix the remaining compiler-rt testsuite bugs on SPARC
(https://reviews.llvm.org/D40900). One of the failures is

Builtins-sparc-sunos :: divtc3_test.c
Builtins-sparcv9-sunos :: divtc3_test.c

While the sparcv9 failure is different, the sparc one boils down to incorrectly
passing long double arguments. Consider the following testcase:

$ cat caller.c
extern void callee (long double);

int
main (void)
{
long double ld = 1.0;

callee (ld);
return 0;
}
$ cat callee.c
extern void abort (void);

void
callee (long double ld)
{
if (ld != 1.0)
abort ();
}
$ clang -m32 -c caller.c -o caller.clang.o
$ clang -m32 -c callee.c -o callee.clang.o
$ gcc -m32 -c caller.c -o caller.gcc.o
$ gcc -m32 -c callee.c -o callee.gcc.o
$ gcc -m32 -o clang-gcc caller.clang.o callee.gcc.o
$ ./clang-gcc
Segmentation Fault (core dumped)
$ gcc -m32 -o gcc-clang caller.gcc.o callee.clang.o
$ ./gcc-clang
Abort (core dumped)

The SPARC psABI, p.3-15 (Structure, Union, and Quad-Precision Arguments)
requires long double args to be passed by reference, while clang passes
them by value (as is correct for SPARCv9).