https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112855
Bug ID: 112855
Summary: [14] RISC-V vector: overwriting stack args
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: patrick at rivosinc dot com
Target Milestone: ---
reduced testcase:
int printf(char *, ...);
int a;
int b = 100;
int c[25];
int d;
int main() {
int e;
d = 0;
for (; d < 5; d++) {
e = 0;
for (; e < 5; e++)
c[d * 5 + e] = 0;
}
if (b)
if (a)
for (;;)
;
b++;
int volatile f = *c;
printf("%d\n", b);
}
Tested using qemu with these commands:
> ./bin/riscv64-unknown-linux-gnu-gcc -march=rv64gcv -mabi=lp64d -O3 red.c -o
> rv64gcv.out
> ./bin/riscv64-unknown-linux-gnu-gcc -march=rv64gc -mabi=lp64d -O3 red.c -o
> rv64gc.out
> QEMU_CPU=rv64,vlen=128,v=true,vext_spec=v1.0,Zve32f=true,Zve64f=true
> ./bin/qemu-riscv64 rv64gc.out
101
> QEMU_CPU=rv64,vlen=128,v=true,vext_spec=v1.0,Zve32f=true,Zve64f=true
> ./bin/qemu-riscv64 rv64gcv.out
5
rv64gcv should match rv64gc and output 101. I'm not sure where it's getting "5"
from.
When you comment out the b++, the behavior is fixed (and both rv64gcv and
rv64gc output 100):
https://godbolt.org/z/chqGo6fj8
Changing other aspects of the program will also fix the behavior, it's just
that commenting out b++ was the least-disruptive change on the assembly code
that I could find.
You can also set b to zero. I just have it at 100 to make it more obvious that
the arg is getting overwritten, not just added/subtracted.
