[BPF] fix sub-register handling for bpf_fastcall #110618
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This issue was causing Linux kernel BPF selftest failure: arena_htab/arena_htab_asm execution logHere register |
bpf_fastcall induced spill/fill pairs should be generated for
sub-register as well as for sub-registers. At the moment this is not
the case, e.g.:
$ cat t.c
extern int foo(void) __attribute__((bpf_fastcall));
int bar(int a) {
foo();
return a;
}
$ clang --target=bpf -mcpu=v3 -O2 -S t.c -o -
...
call foo
w0 = w1
exit
Modify BPFMIPeephole.cpp:collectBPFFastCalls() to check sub-registers
liveness and thus produce correct code for example above:
*(u64 *)(r10 - 8) = r1
call foo
r1 = *(u64 *)(r10 - 8)
w0 = w1
exit
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4ast
approved these changes
Oct 1, 2024
As pointed by @4ast, there is no need to do two calls to `IsLiveBeforeInsn`, LivePhysRegs::contains() is documented as follows: /// ... This also /// works if only the super register of \p Reg has been defined, because /// addReg() always adds all sub-registers to the set as well ...
No changes in behaviour, just makes the code more terse.
Thank you, I'll wait for comments from Yonghong and land after that. |
Sterling-Augustine
pushed a commit
to Sterling-Augustine/llvm-project
that referenced
this pull request
Oct 3, 2024
bpf_fastcall induced spill/fill pairs should be generated for
sub-register as well as for sub-registers. At the moment this is not the
case, e.g.:
$ cat t.c
extern int foo(void) __attribute__((bpf_fastcall));
int bar(int a) {
foo();
return a;
}
$ clang --target=bpf -mcpu=v3 -O2 -S t.c -o -
...
call foo
w0 = w1
exit
Modify BPFMIPeephole.cpp:collectBPFFastCalls() to check sub-registers
liveness and thus produce correct code for example above:
*(u64 *)(r10 - 8) = r1
call foo
r1 = *(u64 *)(r10 - 8)
w0 = w1
exit
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bpf_fastcall induced spill/fill pairs should be generated for sub-register as well as for sub-registers. At the moment this is not the case, e.g.:
Modify BPFMIPeephole.cpp:collectBPFFastCalls() to check sub-registers liveness and thus produce correct code for example above: